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TOMOYO Linux Cross Reference
Linux/fs/namei.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/fs/namei.c
  4  *
  5  *  Copyright (C) 1991, 1992  Linus Torvalds
  6  */
  7 
  8 /*
  9  * Some corrections by tytso.
 10  */
 11 
 12 /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
 13  * lookup logic.
 14  */
 15 /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
 16  */
 17 
 18 #include <linux/init.h>
 19 #include <linux/export.h>
 20 #include <linux/kernel.h>
 21 #include <linux/slab.h>
 22 #include <linux/fs.h>
 23 #include <linux/namei.h>
 24 #include <linux/pagemap.h>
 25 #include <linux/fsnotify.h>
 26 #include <linux/personality.h>
 27 #include <linux/security.h>
 28 #include <linux/ima.h>
 29 #include <linux/syscalls.h>
 30 #include <linux/mount.h>
 31 #include <linux/audit.h>
 32 #include <linux/capability.h>
 33 #include <linux/file.h>
 34 #include <linux/fcntl.h>
 35 #include <linux/device_cgroup.h>
 36 #include <linux/fs_struct.h>
 37 #include <linux/posix_acl.h>
 38 #include <linux/hash.h>
 39 #include <linux/bitops.h>
 40 #include <linux/init_task.h>
 41 #include <linux/uaccess.h>
 42 #include <linux/build_bug.h>
 43 
 44 #include "internal.h"
 45 #include "mount.h"
 46 
 47 /* [Feb-1997 T. Schoebel-Theuer]
 48  * Fundamental changes in the pathname lookup mechanisms (namei)
 49  * were necessary because of omirr.  The reason is that omirr needs
 50  * to know the _real_ pathname, not the user-supplied one, in case
 51  * of symlinks (and also when transname replacements occur).
 52  *
 53  * The new code replaces the old recursive symlink resolution with
 54  * an iterative one (in case of non-nested symlink chains).  It does
 55  * this with calls to <fs>_follow_link().
 56  * As a side effect, dir_namei(), _namei() and follow_link() are now 
 57  * replaced with a single function lookup_dentry() that can handle all 
 58  * the special cases of the former code.
 59  *
 60  * With the new dcache, the pathname is stored at each inode, at least as
 61  * long as the refcount of the inode is positive.  As a side effect, the
 62  * size of the dcache depends on the inode cache and thus is dynamic.
 63  *
 64  * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
 65  * resolution to correspond with current state of the code.
 66  *
 67  * Note that the symlink resolution is not *completely* iterative.
 68  * There is still a significant amount of tail- and mid- recursion in
 69  * the algorithm.  Also, note that <fs>_readlink() is not used in
 70  * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
 71  * may return different results than <fs>_follow_link().  Many virtual
 72  * filesystems (including /proc) exhibit this behavior.
 73  */
 74 
 75 /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
 76  * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
 77  * and the name already exists in form of a symlink, try to create the new
 78  * name indicated by the symlink. The old code always complained that the
 79  * name already exists, due to not following the symlink even if its target
 80  * is nonexistent.  The new semantics affects also mknod() and link() when
 81  * the name is a symlink pointing to a non-existent name.
 82  *
 83  * I don't know which semantics is the right one, since I have no access
 84  * to standards. But I found by trial that HP-UX 9.0 has the full "new"
 85  * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
 86  * "old" one. Personally, I think the new semantics is much more logical.
 87  * Note that "ln old new" where "new" is a symlink pointing to a non-existing
 88  * file does succeed in both HP-UX and SunOs, but not in Solaris
 89  * and in the old Linux semantics.
 90  */
 91 
 92 /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
 93  * semantics.  See the comments in "open_namei" and "do_link" below.
 94  *
 95  * [10-Sep-98 Alan Modra] Another symlink change.
 96  */
 97 
 98 /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
 99  *      inside the path - always follow.
100  *      in the last component in creation/removal/renaming - never follow.
101  *      if LOOKUP_FOLLOW passed - follow.
102  *      if the pathname has trailing slashes - follow.
103  *      otherwise - don't follow.
104  * (applied in that order).
105  *
106  * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
107  * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
108  * During the 2.4 we need to fix the userland stuff depending on it -
109  * hopefully we will be able to get rid of that wart in 2.5. So far only
110  * XEmacs seems to be relying on it...
111  */
112 /*
113  * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
114  * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives
115  * any extra contention...
116  */
117 
118 /* In order to reduce some races, while at the same time doing additional
119  * checking and hopefully speeding things up, we copy filenames to the
120  * kernel data space before using them..
121  *
122  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
123  * PATH_MAX includes the nul terminator --RR.
124  */
125 
126 #define EMBEDDED_NAME_MAX       (PATH_MAX - offsetof(struct filename, iname))
127 
128 struct filename *
129 getname_flags(const char __user *filename, int flags, int *empty)
130 {
131         struct filename *result;
132         char *kname;
133         int len;
134         BUILD_BUG_ON(offsetof(struct filename, iname) % sizeof(long) != 0);
135 
136         result = audit_reusename(filename);
137         if (result)
138                 return result;
139 
140         result = __getname();
141         if (unlikely(!result))
142                 return ERR_PTR(-ENOMEM);
143 
144         /*
145          * First, try to embed the struct filename inside the names_cache
146          * allocation
147          */
148         kname = (char *)result->iname;
149         result->name = kname;
150 
151         len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX);
152         if (unlikely(len < 0)) {
153                 __putname(result);
154                 return ERR_PTR(len);
155         }
156 
157         /*
158          * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
159          * separate struct filename so we can dedicate the entire
160          * names_cache allocation for the pathname, and re-do the copy from
161          * userland.
162          */
163         if (unlikely(len == EMBEDDED_NAME_MAX)) {
164                 const size_t size = offsetof(struct filename, iname[1]);
165                 kname = (char *)result;
166 
167                 /*
168                  * size is chosen that way we to guarantee that
169                  * result->iname[0] is within the same object and that
170                  * kname can't be equal to result->iname, no matter what.
171                  */
172                 result = kzalloc(size, GFP_KERNEL);
173                 if (unlikely(!result)) {
174                         __putname(kname);
175                         return ERR_PTR(-ENOMEM);
176                 }
177                 result->name = kname;
178                 len = strncpy_from_user(kname, filename, PATH_MAX);
179                 if (unlikely(len < 0)) {
180                         __putname(kname);
181                         kfree(result);
182                         return ERR_PTR(len);
183                 }
184                 if (unlikely(len == PATH_MAX)) {
185                         __putname(kname);
186                         kfree(result);
187                         return ERR_PTR(-ENAMETOOLONG);
188                 }
189         }
190 
191         result->refcnt = 1;
192         /* The empty path is special. */
193         if (unlikely(!len)) {
194                 if (empty)
195                         *empty = 1;
196                 if (!(flags & LOOKUP_EMPTY)) {
197                         putname(result);
198                         return ERR_PTR(-ENOENT);
199                 }
200         }
201 
202         result->uptr = filename;
203         result->aname = NULL;
204         audit_getname(result);
205         return result;
206 }
207 
208 struct filename *
209 getname(const char __user * filename)
210 {
211         return getname_flags(filename, 0, NULL);
212 }
213 
214 struct filename *
215 getname_kernel(const char * filename)
216 {
217         struct filename *result;
218         int len = strlen(filename) + 1;
219 
220         result = __getname();
221         if (unlikely(!result))
222                 return ERR_PTR(-ENOMEM);
223 
224         if (len <= EMBEDDED_NAME_MAX) {
225                 result->name = (char *)result->iname;
226         } else if (len <= PATH_MAX) {
227                 const size_t size = offsetof(struct filename, iname[1]);
228                 struct filename *tmp;
229 
230                 tmp = kmalloc(size, GFP_KERNEL);
231                 if (unlikely(!tmp)) {
232                         __putname(result);
233                         return ERR_PTR(-ENOMEM);
234                 }
235                 tmp->name = (char *)result;
236                 result = tmp;
237         } else {
238                 __putname(result);
239                 return ERR_PTR(-ENAMETOOLONG);
240         }
241         memcpy((char *)result->name, filename, len);
242         result->uptr = NULL;
243         result->aname = NULL;
244         result->refcnt = 1;
245         audit_getname(result);
246 
247         return result;
248 }
249 
250 void putname(struct filename *name)
251 {
252         BUG_ON(name->refcnt <= 0);
253 
254         if (--name->refcnt > 0)
255                 return;
256 
257         if (name->name != name->iname) {
258                 __putname(name->name);
259                 kfree(name);
260         } else
261                 __putname(name);
262 }
263 
264 static int check_acl(struct inode *inode, int mask)
265 {
266 #ifdef CONFIG_FS_POSIX_ACL
267         struct posix_acl *acl;
268 
269         if (mask & MAY_NOT_BLOCK) {
270                 acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
271                 if (!acl)
272                         return -EAGAIN;
273                 /* no ->get_acl() calls in RCU mode... */
274                 if (is_uncached_acl(acl))
275                         return -ECHILD;
276                 return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK);
277         }
278 
279         acl = get_acl(inode, ACL_TYPE_ACCESS);
280         if (IS_ERR(acl))
281                 return PTR_ERR(acl);
282         if (acl) {
283                 int error = posix_acl_permission(inode, acl, mask);
284                 posix_acl_release(acl);
285                 return error;
286         }
287 #endif
288 
289         return -EAGAIN;
290 }
291 
292 /*
293  * This does the basic permission checking
294  */
295 static int acl_permission_check(struct inode *inode, int mask)
296 {
297         unsigned int mode = inode->i_mode;
298 
299         if (likely(uid_eq(current_fsuid(), inode->i_uid)))
300                 mode >>= 6;
301         else {
302                 if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
303                         int error = check_acl(inode, mask);
304                         if (error != -EAGAIN)
305                                 return error;
306                 }
307 
308                 if (in_group_p(inode->i_gid))
309                         mode >>= 3;
310         }
311 
312         /*
313          * If the DACs are ok we don't need any capability check.
314          */
315         if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
316                 return 0;
317         return -EACCES;
318 }
319 
320 /**
321  * generic_permission -  check for access rights on a Posix-like filesystem
322  * @inode:      inode to check access rights for
323  * @mask:       right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...)
324  *
325  * Used to check for read/write/execute permissions on a file.
326  * We use "fsuid" for this, letting us set arbitrary permissions
327  * for filesystem access without changing the "normal" uids which
328  * are used for other things.
329  *
330  * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
331  * request cannot be satisfied (eg. requires blocking or too much complexity).
332  * It would then be called again in ref-walk mode.
333  */
334 int generic_permission(struct inode *inode, int mask)
335 {
336         int ret;
337 
338         /*
339          * Do the basic permission checks.
340          */
341         ret = acl_permission_check(inode, mask);
342         if (ret != -EACCES)
343                 return ret;
344 
345         if (S_ISDIR(inode->i_mode)) {
346                 /* DACs are overridable for directories */
347                 if (!(mask & MAY_WRITE))
348                         if (capable_wrt_inode_uidgid(inode,
349                                                      CAP_DAC_READ_SEARCH))
350                                 return 0;
351                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
352                         return 0;
353                 return -EACCES;
354         }
355 
356         /*
357          * Searching includes executable on directories, else just read.
358          */
359         mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
360         if (mask == MAY_READ)
361                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
362                         return 0;
363         /*
364          * Read/write DACs are always overridable.
365          * Executable DACs are overridable when there is
366          * at least one exec bit set.
367          */
368         if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
369                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
370                         return 0;
371 
372         return -EACCES;
373 }
374 EXPORT_SYMBOL(generic_permission);
375 
376 /*
377  * We _really_ want to just do "generic_permission()" without
378  * even looking at the inode->i_op values. So we keep a cache
379  * flag in inode->i_opflags, that says "this has not special
380  * permission function, use the fast case".
381  */
382 static inline int do_inode_permission(struct inode *inode, int mask)
383 {
384         if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) {
385                 if (likely(inode->i_op->permission))
386                         return inode->i_op->permission(inode, mask);
387 
388                 /* This gets set once for the inode lifetime */
389                 spin_lock(&inode->i_lock);
390                 inode->i_opflags |= IOP_FASTPERM;
391                 spin_unlock(&inode->i_lock);
392         }
393         return generic_permission(inode, mask);
394 }
395 
396 /**
397  * sb_permission - Check superblock-level permissions
398  * @sb: Superblock of inode to check permission on
399  * @inode: Inode to check permission on
400  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
401  *
402  * Separate out file-system wide checks from inode-specific permission checks.
403  */
404 static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
405 {
406         if (unlikely(mask & MAY_WRITE)) {
407                 umode_t mode = inode->i_mode;
408 
409                 /* Nobody gets write access to a read-only fs. */
410                 if (sb_rdonly(sb) && (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
411                         return -EROFS;
412         }
413         return 0;
414 }
415 
416 /**
417  * inode_permission - Check for access rights to a given inode
418  * @inode: Inode to check permission on
419  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
420  *
421  * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
422  * this, letting us set arbitrary permissions for filesystem access without
423  * changing the "normal" UIDs which are used for other things.
424  *
425  * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
426  */
427 int inode_permission(struct inode *inode, int mask)
428 {
429         int retval;
430 
431         retval = sb_permission(inode->i_sb, inode, mask);
432         if (retval)
433                 return retval;
434 
435         if (unlikely(mask & MAY_WRITE)) {
436                 /*
437                  * Nobody gets write access to an immutable file.
438                  */
439                 if (IS_IMMUTABLE(inode))
440                         return -EPERM;
441 
442                 /*
443                  * Updating mtime will likely cause i_uid and i_gid to be
444                  * written back improperly if their true value is unknown
445                  * to the vfs.
446                  */
447                 if (HAS_UNMAPPED_ID(inode))
448                         return -EACCES;
449         }
450 
451         retval = do_inode_permission(inode, mask);
452         if (retval)
453                 return retval;
454 
455         retval = devcgroup_inode_permission(inode, mask);
456         if (retval)
457                 return retval;
458 
459         return security_inode_permission(inode, mask);
460 }
461 EXPORT_SYMBOL(inode_permission);
462 
463 /**
464  * path_get - get a reference to a path
465  * @path: path to get the reference to
466  *
467  * Given a path increment the reference count to the dentry and the vfsmount.
468  */
469 void path_get(const struct path *path)
470 {
471         mntget(path->mnt);
472         dget(path->dentry);
473 }
474 EXPORT_SYMBOL(path_get);
475 
476 /**
477  * path_put - put a reference to a path
478  * @path: path to put the reference to
479  *
480  * Given a path decrement the reference count to the dentry and the vfsmount.
481  */
482 void path_put(const struct path *path)
483 {
484         dput(path->dentry);
485         mntput(path->mnt);
486 }
487 EXPORT_SYMBOL(path_put);
488 
489 #define EMBEDDED_LEVELS 2
490 struct nameidata {
491         struct path     path;
492         struct qstr     last;
493         struct path     root;
494         struct inode    *inode; /* path.dentry.d_inode */
495         unsigned int    flags;
496         unsigned        seq, m_seq;
497         int             last_type;
498         unsigned        depth;
499         int             total_link_count;
500         struct saved {
501                 struct path link;
502                 struct delayed_call done;
503                 const char *name;
504                 unsigned seq;
505         } *stack, internal[EMBEDDED_LEVELS];
506         struct filename *name;
507         struct nameidata *saved;
508         struct inode    *link_inode;
509         unsigned        root_seq;
510         int             dfd;
511 } __randomize_layout;
512 
513 static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
514 {
515         struct nameidata *old = current->nameidata;
516         p->stack = p->internal;
517         p->dfd = dfd;
518         p->name = name;
519         p->total_link_count = old ? old->total_link_count : 0;
520         p->saved = old;
521         current->nameidata = p;
522 }
523 
524 static void restore_nameidata(void)
525 {
526         struct nameidata *now = current->nameidata, *old = now->saved;
527 
528         current->nameidata = old;
529         if (old)
530                 old->total_link_count = now->total_link_count;
531         if (now->stack != now->internal)
532                 kfree(now->stack);
533 }
534 
535 static int __nd_alloc_stack(struct nameidata *nd)
536 {
537         struct saved *p;
538 
539         if (nd->flags & LOOKUP_RCU) {
540                 p= kmalloc_array(MAXSYMLINKS, sizeof(struct saved),
541                                   GFP_ATOMIC);
542                 if (unlikely(!p))
543                         return -ECHILD;
544         } else {
545                 p= kmalloc_array(MAXSYMLINKS, sizeof(struct saved),
546                                   GFP_KERNEL);
547                 if (unlikely(!p))
548                         return -ENOMEM;
549         }
550         memcpy(p, nd->internal, sizeof(nd->internal));
551         nd->stack = p;
552         return 0;
553 }
554 
555 /**
556  * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
557  * @path: nameidate to verify
558  *
559  * Rename can sometimes move a file or directory outside of a bind
560  * mount, path_connected allows those cases to be detected.
561  */
562 static bool path_connected(const struct path *path)
563 {
564         struct vfsmount *mnt = path->mnt;
565         struct super_block *sb = mnt->mnt_sb;
566 
567         /* Bind mounts and multi-root filesystems can have disconnected paths */
568         if (!(sb->s_iflags & SB_I_MULTIROOT) && (mnt->mnt_root == sb->s_root))
569                 return true;
570 
571         return is_subdir(path->dentry, mnt->mnt_root);
572 }
573 
574 static inline int nd_alloc_stack(struct nameidata *nd)
575 {
576         if (likely(nd->depth != EMBEDDED_LEVELS))
577                 return 0;
578         if (likely(nd->stack != nd->internal))
579                 return 0;
580         return __nd_alloc_stack(nd);
581 }
582 
583 static void drop_links(struct nameidata *nd)
584 {
585         int i = nd->depth;
586         while (i--) {
587                 struct saved *last = nd->stack + i;
588                 do_delayed_call(&last->done);
589                 clear_delayed_call(&last->done);
590         }
591 }
592 
593 static void terminate_walk(struct nameidata *nd)
594 {
595         drop_links(nd);
596         if (!(nd->flags & LOOKUP_RCU)) {
597                 int i;
598                 path_put(&nd->path);
599                 for (i = 0; i < nd->depth; i++)
600                         path_put(&nd->stack[i].link);
601                 if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
602                         path_put(&nd->root);
603                         nd->root.mnt = NULL;
604                 }
605         } else {
606                 nd->flags &= ~LOOKUP_RCU;
607                 if (!(nd->flags & LOOKUP_ROOT))
608                         nd->root.mnt = NULL;
609                 rcu_read_unlock();
610         }
611         nd->depth = 0;
612 }
613 
614 /* path_put is needed afterwards regardless of success or failure */
615 static bool legitimize_path(struct nameidata *nd,
616                             struct path *path, unsigned seq)
617 {
618         int res = __legitimize_mnt(path->mnt, nd->m_seq);
619         if (unlikely(res)) {
620                 if (res > 0)
621                         path->mnt = NULL;
622                 path->dentry = NULL;
623                 return false;
624         }
625         if (unlikely(!lockref_get_not_dead(&path->dentry->d_lockref))) {
626                 path->dentry = NULL;
627                 return false;
628         }
629         return !read_seqcount_retry(&path->dentry->d_seq, seq);
630 }
631 
632 static bool legitimize_links(struct nameidata *nd)
633 {
634         int i;
635         for (i = 0; i < nd->depth; i++) {
636                 struct saved *last = nd->stack + i;
637                 if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
638                         drop_links(nd);
639                         nd->depth = i + 1;
640                         return false;
641                 }
642         }
643         return true;
644 }
645 
646 /*
647  * Path walking has 2 modes, rcu-walk and ref-walk (see
648  * Documentation/filesystems/path-lookup.txt).  In situations when we can't
649  * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
650  * normal reference counts on dentries and vfsmounts to transition to ref-walk
651  * mode.  Refcounts are grabbed at the last known good point before rcu-walk
652  * got stuck, so ref-walk may continue from there. If this is not successful
653  * (eg. a seqcount has changed), then failure is returned and it's up to caller
654  * to restart the path walk from the beginning in ref-walk mode.
655  */
656 
657 /**
658  * unlazy_walk - try to switch to ref-walk mode.
659  * @nd: nameidata pathwalk data
660  * Returns: 0 on success, -ECHILD on failure
661  *
662  * unlazy_walk attempts to legitimize the current nd->path and nd->root
663  * for ref-walk mode.
664  * Must be called from rcu-walk context.
665  * Nothing should touch nameidata between unlazy_walk() failure and
666  * terminate_walk().
667  */
668 static int unlazy_walk(struct nameidata *nd)
669 {
670         struct dentry *parent = nd->path.dentry;
671 
672         BUG_ON(!(nd->flags & LOOKUP_RCU));
673 
674         nd->flags &= ~LOOKUP_RCU;
675         if (unlikely(!legitimize_links(nd)))
676                 goto out2;
677         if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
678                 goto out1;
679         if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
680                 if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq)))
681                         goto out;
682         }
683         rcu_read_unlock();
684         BUG_ON(nd->inode != parent->d_inode);
685         return 0;
686 
687 out2:
688         nd->path.mnt = NULL;
689         nd->path.dentry = NULL;
690 out1:
691         if (!(nd->flags & LOOKUP_ROOT))
692                 nd->root.mnt = NULL;
693 out:
694         rcu_read_unlock();
695         return -ECHILD;
696 }
697 
698 /**
699  * unlazy_child - try to switch to ref-walk mode.
700  * @nd: nameidata pathwalk data
701  * @dentry: child of nd->path.dentry
702  * @seq: seq number to check dentry against
703  * Returns: 0 on success, -ECHILD on failure
704  *
705  * unlazy_child attempts to legitimize the current nd->path, nd->root and dentry
706  * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
707  * @nd.  Must be called from rcu-walk context.
708  * Nothing should touch nameidata between unlazy_child() failure and
709  * terminate_walk().
710  */
711 static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned seq)
712 {
713         BUG_ON(!(nd->flags & LOOKUP_RCU));
714 
715         nd->flags &= ~LOOKUP_RCU;
716         if (unlikely(!legitimize_links(nd)))
717                 goto out2;
718         if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
719                 goto out2;
720         if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref)))
721                 goto out1;
722 
723         /*
724          * We need to move both the parent and the dentry from the RCU domain
725          * to be properly refcounted. And the sequence number in the dentry
726          * validates *both* dentry counters, since we checked the sequence
727          * number of the parent after we got the child sequence number. So we
728          * know the parent must still be valid if the child sequence number is
729          */
730         if (unlikely(!lockref_get_not_dead(&dentry->d_lockref)))
731                 goto out;
732         if (unlikely(read_seqcount_retry(&dentry->d_seq, seq))) {
733                 rcu_read_unlock();
734                 dput(dentry);
735                 goto drop_root_mnt;
736         }
737         /*
738          * Sequence counts matched. Now make sure that the root is
739          * still valid and get it if required.
740          */
741         if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
742                 if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) {
743                         rcu_read_unlock();
744                         dput(dentry);
745                         return -ECHILD;
746                 }
747         }
748 
749         rcu_read_unlock();
750         return 0;
751 
752 out2:
753         nd->path.mnt = NULL;
754 out1:
755         nd->path.dentry = NULL;
756 out:
757         rcu_read_unlock();
758 drop_root_mnt:
759         if (!(nd->flags & LOOKUP_ROOT))
760                 nd->root.mnt = NULL;
761         return -ECHILD;
762 }
763 
764 static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
765 {
766         if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
767                 return dentry->d_op->d_revalidate(dentry, flags);
768         else
769                 return 1;
770 }
771 
772 /**
773  * complete_walk - successful completion of path walk
774  * @nd:  pointer nameidata
775  *
776  * If we had been in RCU mode, drop out of it and legitimize nd->path.
777  * Revalidate the final result, unless we'd already done that during
778  * the path walk or the filesystem doesn't ask for it.  Return 0 on
779  * success, -error on failure.  In case of failure caller does not
780  * need to drop nd->path.
781  */
782 static int complete_walk(struct nameidata *nd)
783 {
784         struct dentry *dentry = nd->path.dentry;
785         int status;
786 
787         if (nd->flags & LOOKUP_RCU) {
788                 if (!(nd->flags & LOOKUP_ROOT))
789                         nd->root.mnt = NULL;
790                 if (unlikely(unlazy_walk(nd)))
791                         return -ECHILD;
792         }
793 
794         if (likely(!(nd->flags & LOOKUP_JUMPED)))
795                 return 0;
796 
797         if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
798                 return 0;
799 
800         status = dentry->d_op->d_weak_revalidate(dentry, nd->flags);
801         if (status > 0)
802                 return 0;
803 
804         if (!status)
805                 status = -ESTALE;
806 
807         return status;
808 }
809 
810 static void set_root(struct nameidata *nd)
811 {
812         struct fs_struct *fs = current->fs;
813 
814         if (nd->flags & LOOKUP_RCU) {
815                 unsigned seq;
816 
817                 do {
818                         seq = read_seqcount_begin(&fs->seq);
819                         nd->root = fs->root;
820                         nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
821                 } while (read_seqcount_retry(&fs->seq, seq));
822         } else {
823                 get_fs_root(fs, &nd->root);
824         }
825 }
826 
827 static void path_put_conditional(struct path *path, struct nameidata *nd)
828 {
829         dput(path->dentry);
830         if (path->mnt != nd->path.mnt)
831                 mntput(path->mnt);
832 }
833 
834 static inline void path_to_nameidata(const struct path *path,
835                                         struct nameidata *nd)
836 {
837         if (!(nd->flags & LOOKUP_RCU)) {
838                 dput(nd->path.dentry);
839                 if (nd->path.mnt != path->mnt)
840                         mntput(nd->path.mnt);
841         }
842         nd->path.mnt = path->mnt;
843         nd->path.dentry = path->dentry;
844 }
845 
846 static int nd_jump_root(struct nameidata *nd)
847 {
848         if (nd->flags & LOOKUP_RCU) {
849                 struct dentry *d;
850                 nd->path = nd->root;
851                 d = nd->path.dentry;
852                 nd->inode = d->d_inode;
853                 nd->seq = nd->root_seq;
854                 if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
855                         return -ECHILD;
856         } else {
857                 path_put(&nd->path);
858                 nd->path = nd->root;
859                 path_get(&nd->path);
860                 nd->inode = nd->path.dentry->d_inode;
861         }
862         nd->flags |= LOOKUP_JUMPED;
863         return 0;
864 }
865 
866 /*
867  * Helper to directly jump to a known parsed path from ->get_link,
868  * caller must have taken a reference to path beforehand.
869  */
870 void nd_jump_link(struct path *path)
871 {
872         struct nameidata *nd = current->nameidata;
873         path_put(&nd->path);
874 
875         nd->path = *path;
876         nd->inode = nd->path.dentry->d_inode;
877         nd->flags |= LOOKUP_JUMPED;
878 }
879 
880 static inline void put_link(struct nameidata *nd)
881 {
882         struct saved *last = nd->stack + --nd->depth;
883         do_delayed_call(&last->done);
884         if (!(nd->flags & LOOKUP_RCU))
885                 path_put(&last->link);
886 }
887 
888 int sysctl_protected_symlinks __read_mostly = 0;
889 int sysctl_protected_hardlinks __read_mostly = 0;
890 int sysctl_protected_fifos __read_mostly;
891 int sysctl_protected_regular __read_mostly;
892 
893 /**
894  * may_follow_link - Check symlink following for unsafe situations
895  * @nd: nameidata pathwalk data
896  *
897  * In the case of the sysctl_protected_symlinks sysctl being enabled,
898  * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is
899  * in a sticky world-writable directory. This is to protect privileged
900  * processes from failing races against path names that may change out
901  * from under them by way of other users creating malicious symlinks.
902  * It will permit symlinks to be followed only when outside a sticky
903  * world-writable directory, or when the uid of the symlink and follower
904  * match, or when the directory owner matches the symlink's owner.
905  *
906  * Returns 0 if following the symlink is allowed, -ve on error.
907  */
908 static inline int may_follow_link(struct nameidata *nd)
909 {
910         const struct inode *inode;
911         const struct inode *parent;
912         kuid_t puid;
913 
914         if (!sysctl_protected_symlinks)
915                 return 0;
916 
917         /* Allowed if owner and follower match. */
918         inode = nd->link_inode;
919         if (uid_eq(current_cred()->fsuid, inode->i_uid))
920                 return 0;
921 
922         /* Allowed if parent directory not sticky and world-writable. */
923         parent = nd->inode;
924         if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH))
925                 return 0;
926 
927         /* Allowed if parent directory and link owner match. */
928         puid = parent->i_uid;
929         if (uid_valid(puid) && uid_eq(puid, inode->i_uid))
930                 return 0;
931 
932         if (nd->flags & LOOKUP_RCU)
933                 return -ECHILD;
934 
935         audit_inode(nd->name, nd->stack[0].link.dentry, 0);
936         audit_log_link_denied("follow_link");
937         return -EACCES;
938 }
939 
940 /**
941  * safe_hardlink_source - Check for safe hardlink conditions
942  * @inode: the source inode to hardlink from
943  *
944  * Return false if at least one of the following conditions:
945  *    - inode is not a regular file
946  *    - inode is setuid
947  *    - inode is setgid and group-exec
948  *    - access failure for read and write
949  *
950  * Otherwise returns true.
951  */
952 static bool safe_hardlink_source(struct inode *inode)
953 {
954         umode_t mode = inode->i_mode;
955 
956         /* Special files should not get pinned to the filesystem. */
957         if (!S_ISREG(mode))
958                 return false;
959 
960         /* Setuid files should not get pinned to the filesystem. */
961         if (mode & S_ISUID)
962                 return false;
963 
964         /* Executable setgid files should not get pinned to the filesystem. */
965         if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
966                 return false;
967 
968         /* Hardlinking to unreadable or unwritable sources is dangerous. */
969         if (inode_permission(inode, MAY_READ | MAY_WRITE))
970                 return false;
971 
972         return true;
973 }
974 
975 /**
976  * may_linkat - Check permissions for creating a hardlink
977  * @link: the source to hardlink from
978  *
979  * Block hardlink when all of:
980  *  - sysctl_protected_hardlinks enabled
981  *  - fsuid does not match inode
982  *  - hardlink source is unsafe (see safe_hardlink_source() above)
983  *  - not CAP_FOWNER in a namespace with the inode owner uid mapped
984  *
985  * Returns 0 if successful, -ve on error.
986  */
987 static int may_linkat(struct path *link)
988 {
989         struct inode *inode = link->dentry->d_inode;
990 
991         /* Inode writeback is not safe when the uid or gid are invalid. */
992         if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
993                 return -EOVERFLOW;
994 
995         if (!sysctl_protected_hardlinks)
996                 return 0;
997 
998         /* Source inode owner (or CAP_FOWNER) can hardlink all they like,
999          * otherwise, it must be a safe source.
1000          */
1001         if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
1002                 return 0;
1003 
1004         audit_log_link_denied("linkat");
1005         return -EPERM;
1006 }
1007 
1008 /**
1009  * may_create_in_sticky - Check whether an O_CREAT open in a sticky directory
1010  *                        should be allowed, or not, on files that already
1011  *                        exist.
1012  * @dir: the sticky parent directory
1013  * @inode: the inode of the file to open
1014  *
1015  * Block an O_CREAT open of a FIFO (or a regular file) when:
1016  *   - sysctl_protected_fifos (or sysctl_protected_regular) is enabled
1017  *   - the file already exists
1018  *   - we are in a sticky directory
1019  *   - we don't own the file
1020  *   - the owner of the directory doesn't own the file
1021  *   - the directory is world writable
1022  * If the sysctl_protected_fifos (or sysctl_protected_regular) is set to 2
1023  * the directory doesn't have to be world writable: being group writable will
1024  * be enough.
1025  *
1026  * Returns 0 if the open is allowed, -ve on error.
1027  */
1028 static int may_create_in_sticky(struct dentry * const dir,
1029                                 struct inode * const inode)
1030 {
1031         if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) ||
1032             (!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
1033             likely(!(dir->d_inode->i_mode & S_ISVTX)) ||
1034             uid_eq(inode->i_uid, dir->d_inode->i_uid) ||
1035             uid_eq(current_fsuid(), inode->i_uid))
1036                 return 0;
1037 
1038         if (likely(dir->d_inode->i_mode & 0002) ||
1039             (dir->d_inode->i_mode & 0020 &&
1040              ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
1041               (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
1042                 return -EACCES;
1043         }
1044         return 0;
1045 }
1046 
1047 static __always_inline
1048 const char *get_link(struct nameidata *nd)
1049 {
1050         struct saved *last = nd->stack + nd->depth - 1;
1051         struct dentry *dentry = last->link.dentry;
1052         struct inode *inode = nd->link_inode;
1053         int error;
1054         const char *res;
1055 
1056         if (!(nd->flags & LOOKUP_RCU)) {
1057                 touch_atime(&last->link);
1058                 cond_resched();
1059         } else if (atime_needs_update(&last->link, inode)) {
1060                 if (unlikely(unlazy_walk(nd)))
1061                         return ERR_PTR(-ECHILD);
1062                 touch_atime(&last->link);
1063         }
1064 
1065         error = security_inode_follow_link(dentry, inode,
1066                                            nd->flags & LOOKUP_RCU);
1067         if (unlikely(error))
1068                 return ERR_PTR(error);
1069 
1070         nd->last_type = LAST_BIND;
1071         res = inode->i_link;
1072         if (!res) {
1073                 const char * (*get)(struct dentry *, struct inode *,
1074                                 struct delayed_call *);
1075                 get = inode->i_op->get_link;
1076                 if (nd->flags & LOOKUP_RCU) {
1077                         res = get(NULL, inode, &last->done);
1078                         if (res == ERR_PTR(-ECHILD)) {
1079                                 if (unlikely(unlazy_walk(nd)))
1080                                         return ERR_PTR(-ECHILD);
1081                                 res = get(dentry, inode, &last->done);
1082                         }
1083                 } else {
1084                         res = get(dentry, inode, &last->done);
1085                 }
1086                 if (IS_ERR_OR_NULL(res))
1087                         return res;
1088         }
1089         if (*res == '/') {
1090                 if (!nd->root.mnt)
1091                         set_root(nd);
1092                 if (unlikely(nd_jump_root(nd)))
1093                         return ERR_PTR(-ECHILD);
1094                 while (unlikely(*++res == '/'))
1095                         ;
1096         }
1097         if (!*res)
1098                 res = NULL;
1099         return res;
1100 }
1101 
1102 /*
1103  * follow_up - Find the mountpoint of path's vfsmount
1104  *
1105  * Given a path, find the mountpoint of its source file system.
1106  * Replace @path with the path of the mountpoint in the parent mount.
1107  * Up is towards /.
1108  *
1109  * Return 1 if we went up a level and 0 if we were already at the
1110  * root.
1111  */
1112 int follow_up(struct path *path)
1113 {
1114         struct mount *mnt = real_mount(path->mnt);
1115         struct mount *parent;
1116         struct dentry *mountpoint;
1117 
1118         read_seqlock_excl(&mount_lock);
1119         parent = mnt->mnt_parent;
1120         if (parent == mnt) {
1121                 read_sequnlock_excl(&mount_lock);
1122                 return 0;
1123         }
1124         mntget(&parent->mnt);
1125         mountpoint = dget(mnt->mnt_mountpoint);
1126         read_sequnlock_excl(&mount_lock);
1127         dput(path->dentry);
1128         path->dentry = mountpoint;
1129         mntput(path->mnt);
1130         path->mnt = &parent->mnt;
1131         return 1;
1132 }
1133 EXPORT_SYMBOL(follow_up);
1134 
1135 /*
1136  * Perform an automount
1137  * - return -EISDIR to tell follow_managed() to stop and return the path we
1138  *   were called with.
1139  */
1140 static int follow_automount(struct path *path, struct nameidata *nd,
1141                             bool *need_mntput)
1142 {
1143         struct vfsmount *mnt;
1144         int err;
1145 
1146         if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
1147                 return -EREMOTE;
1148 
1149         /* We don't want to mount if someone's just doing a stat -
1150          * unless they're stat'ing a directory and appended a '/' to
1151          * the name.
1152          *
1153          * We do, however, want to mount if someone wants to open or
1154          * create a file of any type under the mountpoint, wants to
1155          * traverse through the mountpoint or wants to open the
1156          * mounted directory.  Also, autofs may mark negative dentries
1157          * as being automount points.  These will need the attentions
1158          * of the daemon to instantiate them before they can be used.
1159          */
1160         if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
1161                            LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
1162             path->dentry->d_inode)
1163                 return -EISDIR;
1164 
1165         nd->total_link_count++;
1166         if (nd->total_link_count >= 40)
1167                 return -ELOOP;
1168 
1169         mnt = path->dentry->d_op->d_automount(path);
1170         if (IS_ERR(mnt)) {
1171                 /*
1172                  * The filesystem is allowed to return -EISDIR here to indicate
1173                  * it doesn't want to automount.  For instance, autofs would do
1174                  * this so that its userspace daemon can mount on this dentry.
1175                  *
1176                  * However, we can only permit this if it's a terminal point in
1177                  * the path being looked up; if it wasn't then the remainder of
1178                  * the path is inaccessible and we should say so.
1179                  */
1180                 if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))
1181                         return -EREMOTE;
1182                 return PTR_ERR(mnt);
1183         }
1184 
1185         if (!mnt) /* mount collision */
1186                 return 0;
1187 
1188         if (!*need_mntput) {
1189                 /* lock_mount() may release path->mnt on error */
1190                 mntget(path->mnt);
1191                 *need_mntput = true;
1192         }
1193         err = finish_automount(mnt, path);
1194 
1195         switch (err) {
1196         case -EBUSY:
1197                 /* Someone else made a mount here whilst we were busy */
1198                 return 0;
1199         case 0:
1200                 path_put(path);
1201                 path->mnt = mnt;
1202                 path->dentry = dget(mnt->mnt_root);
1203                 return 0;
1204         default:
1205                 return err;
1206         }
1207 
1208 }
1209 
1210 /*
1211  * Handle a dentry that is managed in some way.
1212  * - Flagged for transit management (autofs)
1213  * - Flagged as mountpoint
1214  * - Flagged as automount point
1215  *
1216  * This may only be called in refwalk mode.
1217  *
1218  * Serialization is taken care of in namespace.c
1219  */
1220 static int follow_managed(struct path *path, struct nameidata *nd)
1221 {
1222         struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
1223         unsigned managed;
1224         bool need_mntput = false;
1225         int ret = 0;
1226 
1227         /* Given that we're not holding a lock here, we retain the value in a
1228          * local variable for each dentry as we look at it so that we don't see
1229          * the components of that value change under us */
1230         while (managed = READ_ONCE(path->dentry->d_flags),
1231                managed &= DCACHE_MANAGED_DENTRY,
1232                unlikely(managed != 0)) {
1233                 /* Allow the filesystem to manage the transit without i_mutex
1234                  * being held. */
1235                 if (managed & DCACHE_MANAGE_TRANSIT) {
1236                         BUG_ON(!path->dentry->d_op);
1237                         BUG_ON(!path->dentry->d_op->d_manage);
1238                         ret = path->dentry->d_op->d_manage(path, false);
1239                         if (ret < 0)
1240                                 break;
1241                 }
1242 
1243                 /* Transit to a mounted filesystem. */
1244                 if (managed & DCACHE_MOUNTED) {
1245                         struct vfsmount *mounted = lookup_mnt(path);
1246                         if (mounted) {
1247                                 dput(path->dentry);
1248                                 if (need_mntput)
1249                                         mntput(path->mnt);
1250                                 path->mnt = mounted;
1251                                 path->dentry = dget(mounted->mnt_root);
1252                                 need_mntput = true;
1253                                 continue;
1254                         }
1255 
1256                         /* Something is mounted on this dentry in another
1257                          * namespace and/or whatever was mounted there in this
1258                          * namespace got unmounted before lookup_mnt() could
1259                          * get it */
1260                 }
1261 
1262                 /* Handle an automount point */
1263                 if (managed & DCACHE_NEED_AUTOMOUNT) {
1264                         ret = follow_automount(path, nd, &need_mntput);
1265                         if (ret < 0)
1266                                 break;
1267                         continue;
1268                 }
1269 
1270                 /* We didn't change the current path point */
1271                 break;
1272         }
1273 
1274         if (need_mntput && path->mnt == mnt)
1275                 mntput(path->mnt);
1276         if (ret == -EISDIR || !ret)
1277                 ret = 1;
1278         if (need_mntput)
1279                 nd->flags |= LOOKUP_JUMPED;
1280         if (unlikely(ret < 0))
1281                 path_put_conditional(path, nd);
1282         return ret;
1283 }
1284 
1285 int follow_down_one(struct path *path)
1286 {
1287         struct vfsmount *mounted;
1288 
1289         mounted = lookup_mnt(path);
1290         if (mounted) {
1291                 dput(path->dentry);
1292                 mntput(path->mnt);
1293                 path->mnt = mounted;
1294                 path->dentry = dget(mounted->mnt_root);
1295                 return 1;
1296         }
1297         return 0;
1298 }
1299 EXPORT_SYMBOL(follow_down_one);
1300 
1301 static inline int managed_dentry_rcu(const struct path *path)
1302 {
1303         return (path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
1304                 path->dentry->d_op->d_manage(path, true) : 0;
1305 }
1306 
1307 /*
1308  * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
1309  * we meet a managed dentry that would need blocking.
1310  */
1311 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
1312                                struct inode **inode, unsigned *seqp)
1313 {
1314         for (;;) {
1315                 struct mount *mounted;
1316                 /*
1317                  * Don't forget we might have a non-mountpoint managed dentry
1318                  * that wants to block transit.
1319                  */
1320                 switch (managed_dentry_rcu(path)) {
1321                 case -ECHILD:
1322                 default:
1323                         return false;
1324                 case -EISDIR:
1325                         return true;
1326                 case 0:
1327                         break;
1328                 }
1329 
1330                 if (!d_mountpoint(path->dentry))
1331                         return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1332 
1333                 mounted = __lookup_mnt(path->mnt, path->dentry);
1334                 if (!mounted)
1335                         break;
1336                 path->mnt = &mounted->mnt;
1337                 path->dentry = mounted->mnt.mnt_root;
1338                 nd->flags |= LOOKUP_JUMPED;
1339                 *seqp = read_seqcount_begin(&path->dentry->d_seq);
1340                 /*
1341                  * Update the inode too. We don't need to re-check the
1342                  * dentry sequence number here after this d_inode read,
1343                  * because a mount-point is always pinned.
1344                  */
1345                 *inode = path->dentry->d_inode;
1346         }
1347         return !read_seqretry(&mount_lock, nd->m_seq) &&
1348                 !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1349 }
1350 
1351 static int follow_dotdot_rcu(struct nameidata *nd)
1352 {
1353         struct inode *inode = nd->inode;
1354 
1355         while (1) {
1356                 if (path_equal(&nd->path, &nd->root))
1357                         break;
1358                 if (nd->path.dentry != nd->path.mnt->mnt_root) {
1359                         struct dentry *old = nd->path.dentry;
1360                         struct dentry *parent = old->d_parent;
1361                         unsigned seq;
1362 
1363                         inode = parent->d_inode;
1364                         seq = read_seqcount_begin(&parent->d_seq);
1365                         if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))
1366                                 return -ECHILD;
1367                         nd->path.dentry = parent;
1368                         nd->seq = seq;
1369                         if (unlikely(!path_connected(&nd->path)))
1370                                 return -ENOENT;
1371                         break;
1372                 } else {
1373                         struct mount *mnt = real_mount(nd->path.mnt);
1374                         struct mount *mparent = mnt->mnt_parent;
1375                         struct dentry *mountpoint = mnt->mnt_mountpoint;
1376                         struct inode *inode2 = mountpoint->d_inode;
1377                         unsigned seq = read_seqcount_begin(&mountpoint->d_seq);
1378                         if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1379                                 return -ECHILD;
1380                         if (&mparent->mnt == nd->path.mnt)
1381                                 break;
1382                         /* we know that mountpoint was pinned */
1383                         nd->path.dentry = mountpoint;
1384                         nd->path.mnt = &mparent->mnt;
1385                         inode = inode2;
1386                         nd->seq = seq;
1387                 }
1388         }
1389         while (unlikely(d_mountpoint(nd->path.dentry))) {
1390                 struct mount *mounted;
1391                 mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry);
1392                 if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1393                         return -ECHILD;
1394                 if (!mounted)
1395                         break;
1396                 nd->path.mnt = &mounted->mnt;
1397                 nd->path.dentry = mounted->mnt.mnt_root;
1398                 inode = nd->path.dentry->d_inode;
1399                 nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
1400         }
1401         nd->inode = inode;
1402         return 0;
1403 }
1404 
1405 /*
1406  * Follow down to the covering mount currently visible to userspace.  At each
1407  * point, the filesystem owning that dentry may be queried as to whether the
1408  * caller is permitted to proceed or not.
1409  */
1410 int follow_down(struct path *path)
1411 {
1412         unsigned managed;
1413         int ret;
1414 
1415         while (managed = READ_ONCE(path->dentry->d_flags),
1416                unlikely(managed & DCACHE_MANAGED_DENTRY)) {
1417                 /* Allow the filesystem to manage the transit without i_mutex
1418                  * being held.
1419                  *
1420                  * We indicate to the filesystem if someone is trying to mount
1421                  * something here.  This gives autofs the chance to deny anyone
1422                  * other than its daemon the right to mount on its
1423                  * superstructure.
1424                  *
1425                  * The filesystem may sleep at this point.
1426                  */
1427                 if (managed & DCACHE_MANAGE_TRANSIT) {
1428                         BUG_ON(!path->dentry->d_op);
1429                         BUG_ON(!path->dentry->d_op->d_manage);
1430                         ret = path->dentry->d_op->d_manage(path, false);
1431                         if (ret < 0)
1432                                 return ret == -EISDIR ? 0 : ret;
1433                 }
1434 
1435                 /* Transit to a mounted filesystem. */
1436                 if (managed & DCACHE_MOUNTED) {
1437                         struct vfsmount *mounted = lookup_mnt(path);
1438                         if (!mounted)
1439                                 break;
1440                         dput(path->dentry);
1441                         mntput(path->mnt);
1442                         path->mnt = mounted;
1443                         path->dentry = dget(mounted->mnt_root);
1444                         continue;
1445                 }
1446 
1447                 /* Don't handle automount points here */
1448                 break;
1449         }
1450         return 0;
1451 }
1452 EXPORT_SYMBOL(follow_down);
1453 
1454 /*
1455  * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
1456  */
1457 static void follow_mount(struct path *path)
1458 {
1459         while (d_mountpoint(path->dentry)) {
1460                 struct vfsmount *mounted = lookup_mnt(path);
1461                 if (!mounted)
1462                         break;
1463                 dput(path->dentry);
1464                 mntput(path->mnt);
1465                 path->mnt = mounted;
1466                 path->dentry = dget(mounted->mnt_root);
1467         }
1468 }
1469 
1470 static int path_parent_directory(struct path *path)
1471 {
1472         struct dentry *old = path->dentry;
1473         /* rare case of legitimate dget_parent()... */
1474         path->dentry = dget_parent(path->dentry);
1475         dput(old);
1476         if (unlikely(!path_connected(path)))
1477                 return -ENOENT;
1478         return 0;
1479 }
1480 
1481 static int follow_dotdot(struct nameidata *nd)
1482 {
1483         while(1) {
1484                 if (path_equal(&nd->path, &nd->root))
1485                         break;
1486                 if (nd->path.dentry != nd->path.mnt->mnt_root) {
1487                         int ret = path_parent_directory(&nd->path);
1488                         if (ret)
1489                                 return ret;
1490                         break;
1491                 }
1492                 if (!follow_up(&nd->path))
1493                         break;
1494         }
1495         follow_mount(&nd->path);
1496         nd->inode = nd->path.dentry->d_inode;
1497         return 0;
1498 }
1499 
1500 /*
1501  * This looks up the name in dcache and possibly revalidates the found dentry.
1502  * NULL is returned if the dentry does not exist in the cache.
1503  */
1504 static struct dentry *lookup_dcache(const struct qstr *name,
1505                                     struct dentry *dir,
1506                                     unsigned int flags)
1507 {
1508         struct dentry *dentry = d_lookup(dir, name);
1509         if (dentry) {
1510                 int error = d_revalidate(dentry, flags);
1511                 if (unlikely(error <= 0)) {
1512                         if (!error)
1513                                 d_invalidate(dentry);
1514                         dput(dentry);
1515                         return ERR_PTR(error);
1516                 }
1517         }
1518         return dentry;
1519 }
1520 
1521 /*
1522  * Parent directory has inode locked exclusive.  This is one
1523  * and only case when ->lookup() gets called on non in-lookup
1524  * dentries - as the matter of fact, this only gets called
1525  * when directory is guaranteed to have no in-lookup children
1526  * at all.
1527  */
1528 static struct dentry *__lookup_hash(const struct qstr *name,
1529                 struct dentry *base, unsigned int flags)
1530 {
1531         struct dentry *dentry = lookup_dcache(name, base, flags);
1532         struct dentry *old;
1533         struct inode *dir = base->d_inode;
1534 
1535         if (dentry)
1536                 return dentry;
1537 
1538         /* Don't create child dentry for a dead directory. */
1539         if (unlikely(IS_DEADDIR(dir)))
1540                 return ERR_PTR(-ENOENT);
1541 
1542         dentry = d_alloc(base, name);
1543         if (unlikely(!dentry))
1544                 return ERR_PTR(-ENOMEM);
1545 
1546         old = dir->i_op->lookup(dir, dentry, flags);
1547         if (unlikely(old)) {
1548                 dput(dentry);
1549                 dentry = old;
1550         }
1551         return dentry;
1552 }
1553 
1554 static int lookup_fast(struct nameidata *nd,
1555                        struct path *path, struct inode **inode,
1556                        unsigned *seqp)
1557 {
1558         struct vfsmount *mnt = nd->path.mnt;
1559         struct dentry *dentry, *parent = nd->path.dentry;
1560         int status = 1;
1561         int err;
1562 
1563         /*
1564          * Rename seqlock is not required here because in the off chance
1565          * of a false negative due to a concurrent rename, the caller is
1566          * going to fall back to non-racy lookup.
1567          */
1568         if (nd->flags & LOOKUP_RCU) {
1569                 unsigned seq;
1570                 bool negative;
1571                 dentry = __d_lookup_rcu(parent, &nd->last, &seq);
1572                 if (unlikely(!dentry)) {
1573                         if (unlazy_walk(nd))
1574                                 return -ECHILD;
1575                         return 0;
1576                 }
1577 
1578                 /*
1579                  * This sequence count validates that the inode matches
1580                  * the dentry name information from lookup.
1581                  */
1582                 *inode = d_backing_inode(dentry);
1583                 negative = d_is_negative(dentry);
1584                 if (unlikely(read_seqcount_retry(&dentry->d_seq, seq)))
1585                         return -ECHILD;
1586 
1587                 /*
1588                  * This sequence count validates that the parent had no
1589                  * changes while we did the lookup of the dentry above.
1590                  *
1591                  * The memory barrier in read_seqcount_begin of child is
1592                  *  enough, we can use __read_seqcount_retry here.
1593                  */
1594                 if (unlikely(__read_seqcount_retry(&parent->d_seq, nd->seq)))
1595                         return -ECHILD;
1596 
1597                 *seqp = seq;
1598                 status = d_revalidate(dentry, nd->flags);
1599                 if (likely(status > 0)) {
1600                         /*
1601                          * Note: do negative dentry check after revalidation in
1602                          * case that drops it.
1603                          */
1604                         if (unlikely(negative))
1605                                 return -ENOENT;
1606                         path->mnt = mnt;
1607                         path->dentry = dentry;
1608                         if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
1609                                 return 1;
1610                 }
1611                 if (unlazy_child(nd, dentry, seq))
1612                         return -ECHILD;
1613                 if (unlikely(status == -ECHILD))
1614                         /* we'd been told to redo it in non-rcu mode */
1615                         status = d_revalidate(dentry, nd->flags);
1616         } else {
1617                 dentry = __d_lookup(parent, &nd->last);
1618                 if (unlikely(!dentry))
1619                         return 0;
1620                 status = d_revalidate(dentry, nd->flags);
1621         }
1622         if (unlikely(status <= 0)) {
1623                 if (!status)
1624                         d_invalidate(dentry);
1625                 dput(dentry);
1626                 return status;
1627         }
1628         if (unlikely(d_is_negative(dentry))) {
1629                 dput(dentry);
1630                 return -ENOENT;
1631         }
1632 
1633         path->mnt = mnt;
1634         path->dentry = dentry;
1635         err = follow_managed(path, nd);
1636         if (likely(err > 0))
1637                 *inode = d_backing_inode(path->dentry);
1638         return err;
1639 }
1640 
1641 /* Fast lookup failed, do it the slow way */
1642 static struct dentry *__lookup_slow(const struct qstr *name,
1643                                     struct dentry *dir,
1644                                     unsigned int flags)
1645 {
1646         struct dentry *dentry, *old;
1647         struct inode *inode = dir->d_inode;
1648         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
1649 
1650         /* Don't go there if it's already dead */
1651         if (unlikely(IS_DEADDIR(inode)))
1652                 return ERR_PTR(-ENOENT);
1653 again:
1654         dentry = d_alloc_parallel(dir, name, &wq);
1655         if (IS_ERR(dentry))
1656                 return dentry;
1657         if (unlikely(!d_in_lookup(dentry))) {
1658                 if (!(flags & LOOKUP_NO_REVAL)) {
1659                         int error = d_revalidate(dentry, flags);
1660                         if (unlikely(error <= 0)) {
1661                                 if (!error) {
1662                                         d_invalidate(dentry);
1663                                         dput(dentry);
1664                                         goto again;
1665                                 }
1666                                 dput(dentry);
1667                                 dentry = ERR_PTR(error);
1668                         }
1669                 }
1670         } else {
1671                 old = inode->i_op->lookup(inode, dentry, flags);
1672                 d_lookup_done(dentry);
1673                 if (unlikely(old)) {
1674                         dput(dentry);
1675                         dentry = old;
1676                 }
1677         }
1678         return dentry;
1679 }
1680 
1681 static struct dentry *lookup_slow(const struct qstr *name,
1682                                   struct dentry *dir,
1683                                   unsigned int flags)
1684 {
1685         struct inode *inode = dir->d_inode;
1686         struct dentry *res;
1687         inode_lock_shared(inode);
1688         res = __lookup_slow(name, dir, flags);
1689         inode_unlock_shared(inode);
1690         return res;
1691 }
1692 
1693 static inline int may_lookup(struct nameidata *nd)
1694 {
1695         if (nd->flags & LOOKUP_RCU) {
1696                 int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
1697                 if (err != -ECHILD)
1698                         return err;
1699                 if (unlazy_walk(nd))
1700                         return -ECHILD;
1701         }
1702         return inode_permission(nd->inode, MAY_EXEC);
1703 }
1704 
1705 static inline int handle_dots(struct nameidata *nd, int type)
1706 {
1707         if (type == LAST_DOTDOT) {
1708                 if (!nd->root.mnt)
1709                         set_root(nd);
1710                 if (nd->flags & LOOKUP_RCU) {
1711                         return follow_dotdot_rcu(nd);
1712                 } else
1713                         return follow_dotdot(nd);
1714         }
1715         return 0;
1716 }
1717 
1718 static int pick_link(struct nameidata *nd, struct path *link,
1719                      struct inode *inode, unsigned seq)
1720 {
1721         int error;
1722         struct saved *last;
1723         if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
1724                 path_to_nameidata(link, nd);
1725                 return -ELOOP;
1726         }
1727         if (!(nd->flags & LOOKUP_RCU)) {
1728                 if (link->mnt == nd->path.mnt)
1729                         mntget(link->mnt);
1730         }
1731         error = nd_alloc_stack(nd);
1732         if (unlikely(error)) {
1733                 if (error == -ECHILD) {
1734                         if (unlikely(!legitimize_path(nd, link, seq))) {
1735                                 drop_links(nd);
1736                                 nd->depth = 0;
1737                                 nd->flags &= ~LOOKUP_RCU;
1738                                 nd->path.mnt = NULL;
1739                                 nd->path.dentry = NULL;
1740                                 if (!(nd->flags & LOOKUP_ROOT))
1741                                         nd->root.mnt = NULL;
1742                                 rcu_read_unlock();
1743                         } else if (likely(unlazy_walk(nd)) == 0)
1744                                 error = nd_alloc_stack(nd);
1745                 }
1746                 if (error) {
1747                         path_put(link);
1748                         return error;
1749                 }
1750         }
1751 
1752         last = nd->stack + nd->depth++;
1753         last->link = *link;
1754         clear_delayed_call(&last->done);
1755         nd->link_inode = inode;
1756         last->seq = seq;
1757         return 1;
1758 }
1759 
1760 enum {WALK_FOLLOW = 1, WALK_MORE = 2};
1761 
1762 /*
1763  * Do we need to follow links? We _really_ want to be able
1764  * to do this check without having to look at inode->i_op,
1765  * so we keep a cache of "no, this doesn't need follow_link"
1766  * for the common case.
1767  */
1768 static inline int step_into(struct nameidata *nd, struct path *path,
1769                             int flags, struct inode *inode, unsigned seq)
1770 {
1771         if (!(flags & WALK_MORE) && nd->depth)
1772                 put_link(nd);
1773         if (likely(!d_is_symlink(path->dentry)) ||
1774            !(flags & WALK_FOLLOW || nd->flags & LOOKUP_FOLLOW)) {
1775                 /* not a symlink or should not follow */
1776                 path_to_nameidata(path, nd);
1777                 nd->inode = inode;
1778                 nd->seq = seq;
1779                 return 0;
1780         }
1781         /* make sure that d_is_symlink above matches inode */
1782         if (nd->flags & LOOKUP_RCU) {
1783                 if (read_seqcount_retry(&path->dentry->d_seq, seq))
1784                         return -ECHILD;
1785         }
1786         return pick_link(nd, path, inode, seq);
1787 }
1788 
1789 static int walk_component(struct nameidata *nd, int flags)
1790 {
1791         struct path path;
1792         struct inode *inode;
1793         unsigned seq;
1794         int err;
1795         /*
1796          * "." and ".." are special - ".." especially so because it has
1797          * to be able to know about the current root directory and
1798          * parent relationships.
1799          */
1800         if (unlikely(nd->last_type != LAST_NORM)) {
1801                 err = handle_dots(nd, nd->last_type);
1802                 if (!(flags & WALK_MORE) && nd->depth)
1803                         put_link(nd);
1804                 return err;
1805         }
1806         err = lookup_fast(nd, &path, &inode, &seq);
1807         if (unlikely(err <= 0)) {
1808                 if (err < 0)
1809                         return err;
1810                 path.dentry = lookup_slow(&nd->last, nd->path.dentry,
1811                                           nd->flags);
1812                 if (IS_ERR(path.dentry))
1813                         return PTR_ERR(path.dentry);
1814 
1815                 path.mnt = nd->path.mnt;
1816                 err = follow_managed(&path, nd);
1817                 if (unlikely(err < 0))
1818                         return err;
1819 
1820                 if (unlikely(d_is_negative(path.dentry))) {
1821                         path_to_nameidata(&path, nd);
1822                         return -ENOENT;
1823                 }
1824 
1825                 seq = 0;        /* we are already out of RCU mode */
1826                 inode = d_backing_inode(path.dentry);
1827         }
1828 
1829         return step_into(nd, &path, flags, inode, seq);
1830 }
1831 
1832 /*
1833  * We can do the critical dentry name comparison and hashing
1834  * operations one word at a time, but we are limited to:
1835  *
1836  * - Architectures with fast unaligned word accesses. We could
1837  *   do a "get_unaligned()" if this helps and is sufficiently
1838  *   fast.
1839  *
1840  * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
1841  *   do not trap on the (extremely unlikely) case of a page
1842  *   crossing operation.
1843  *
1844  * - Furthermore, we need an efficient 64-bit compile for the
1845  *   64-bit case in order to generate the "number of bytes in
1846  *   the final mask". Again, that could be replaced with a
1847  *   efficient population count instruction or similar.
1848  */
1849 #ifdef CONFIG_DCACHE_WORD_ACCESS
1850 
1851 #include <asm/word-at-a-time.h>
1852 
1853 #ifdef HASH_MIX
1854 
1855 /* Architecture provides HASH_MIX and fold_hash() in <asm/hash.h> */
1856 
1857 #elif defined(CONFIG_64BIT)
1858 /*
1859  * Register pressure in the mixing function is an issue, particularly
1860  * on 32-bit x86, but almost any function requires one state value and
1861  * one temporary.  Instead, use a function designed for two state values
1862  * and no temporaries.
1863  *
1864  * This function cannot create a collision in only two iterations, so
1865  * we have two iterations to achieve avalanche.  In those two iterations,
1866  * we have six layers of mixing, which is enough to spread one bit's
1867  * influence out to 2^6 = 64 state bits.
1868  *
1869  * Rotate constants are scored by considering either 64 one-bit input
1870  * deltas or 64*63/2 = 2016 two-bit input deltas, and finding the
1871  * probability of that delta causing a change to each of the 128 output
1872  * bits, using a sample of random initial states.
1873  *
1874  * The Shannon entropy of the computed probabilities is then summed
1875  * to produce a score.  Ideally, any input change has a 50% chance of
1876  * toggling any given output bit.
1877  *
1878  * Mixing scores (in bits) for (12,45):
1879  * Input delta: 1-bit      2-bit
1880  * 1 round:     713.3    42542.6
1881  * 2 rounds:   2753.7   140389.8
1882  * 3 rounds:   5954.1   233458.2
1883  * 4 rounds:   7862.6   256672.2
1884  * Perfect:    8192     258048
1885  *            (64*128) (64*63/2 * 128)
1886  */
1887 #define HASH_MIX(x, y, a)       \
1888         (       x ^= (a),       \
1889         y ^= x, x = rol64(x,12),\
1890         x += y, y = rol64(y,45),\
1891         y *= 9                  )
1892 
1893 /*
1894  * Fold two longs into one 32-bit hash value.  This must be fast, but
1895  * latency isn't quite as critical, as there is a fair bit of additional
1896  * work done before the hash value is used.
1897  */
1898 static inline unsigned int fold_hash(unsigned long x, unsigned long y)
1899 {
1900         y ^= x * GOLDEN_RATIO_64;
1901         y *= GOLDEN_RATIO_64;
1902         return y >> 32;
1903 }
1904 
1905 #else   /* 32-bit case */
1906 
1907 /*
1908  * Mixing scores (in bits) for (7,20):
1909  * Input delta: 1-bit      2-bit
1910  * 1 round:     330.3     9201.6
1911  * 2 rounds:   1246.4    25475.4
1912  * 3 rounds:   1907.1    31295.1
1913  * 4 rounds:   2042.3    31718.6
1914  * Perfect:    2048      31744
1915  *            (32*64)   (32*31/2 * 64)
1916  */
1917 #define HASH_MIX(x, y, a)       \
1918         (       x ^= (a),       \
1919         y ^= x, x = rol32(x, 7),\
1920         x += y, y = rol32(y,20),\
1921         y *= 9                  )
1922 
1923 static inline unsigned int fold_hash(unsigned long x, unsigned long y)
1924 {
1925         /* Use arch-optimized multiply if one exists */
1926         return __hash_32(y ^ __hash_32(x));
1927 }
1928 
1929 #endif
1930 
1931 /*
1932  * Return the hash of a string of known length.  This is carfully
1933  * designed to match hash_name(), which is the more critical function.
1934  * In particular, we must end by hashing a final word containing 0..7
1935  * payload bytes, to match the way that hash_name() iterates until it
1936  * finds the delimiter after the name.
1937  */
1938 unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
1939 {
1940         unsigned long a, x = 0, y = (unsigned long)salt;
1941 
1942         for (;;) {
1943                 if (!len)
1944                         goto done;
1945                 a = load_unaligned_zeropad(name);
1946                 if (len < sizeof(unsigned long))
1947                         break;
1948                 HASH_MIX(x, y, a);
1949                 name += sizeof(unsigned long);
1950                 len -= sizeof(unsigned long);
1951         }
1952         x ^= a & bytemask_from_count(len);
1953 done:
1954         return fold_hash(x, y);
1955 }
1956 EXPORT_SYMBOL(full_name_hash);
1957 
1958 /* Return the "hash_len" (hash and length) of a null-terminated string */
1959 u64 hashlen_string(const void *salt, const char *name)
1960 {
1961         unsigned long a = 0, x = 0, y = (unsigned long)salt;
1962         unsigned long adata, mask, len;
1963         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
1964 
1965         len = 0;
1966         goto inside;
1967 
1968         do {
1969                 HASH_MIX(x, y, a);
1970                 len += sizeof(unsigned long);
1971 inside:
1972                 a = load_unaligned_zeropad(name+len);
1973         } while (!has_zero(a, &adata, &constants));
1974 
1975         adata = prep_zero_mask(a, adata, &constants);
1976         mask = create_zero_mask(adata);
1977         x ^= a & zero_bytemask(mask);
1978 
1979         return hashlen_create(fold_hash(x, y), len + find_zero(mask));
1980 }
1981 EXPORT_SYMBOL(hashlen_string);
1982 
1983 /*
1984  * Calculate the length and hash of the path component, and
1985  * return the "hash_len" as the result.
1986  */
1987 static inline u64 hash_name(const void *salt, const char *name)
1988 {
1989         unsigned long a = 0, b, x = 0, y = (unsigned long)salt;
1990         unsigned long adata, bdata, mask, len;
1991         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
1992 
1993         len = 0;
1994         goto inside;
1995 
1996         do {
1997                 HASH_MIX(x, y, a);
1998                 len += sizeof(unsigned long);
1999 inside:
2000                 a = load_unaligned_zeropad(name+len);
2001                 b = a ^ REPEAT_BYTE('/');
2002         } while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
2003 
2004         adata = prep_zero_mask(a, adata, &constants);
2005         bdata = prep_zero_mask(b, bdata, &constants);
2006         mask = create_zero_mask(adata | bdata);
2007         x ^= a & zero_bytemask(mask);
2008 
2009         return hashlen_create(fold_hash(x, y), len + find_zero(mask));
2010 }
2011 
2012 #else   /* !CONFIG_DCACHE_WORD_ACCESS: Slow, byte-at-a-time version */
2013 
2014 /* Return the hash of a string of known length */
2015 unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
2016 {
2017         unsigned long hash = init_name_hash(salt);
2018         while (len--)
2019                 hash = partial_name_hash((unsigned char)*name++, hash);
2020         return end_name_hash(hash);
2021 }
2022 EXPORT_SYMBOL(full_name_hash);
2023 
2024 /* Return the "hash_len" (hash and length) of a null-terminated string */
2025 u64 hashlen_string(const void *salt, const char *name)
2026 {
2027         unsigned long hash = init_name_hash(salt);
2028         unsigned long len = 0, c;
2029 
2030         c = (unsigned char)*name;
2031         while (c) {
2032                 len++;
2033                 hash = partial_name_hash(c, hash);
2034                 c = (unsigned char)name[len];
2035         }
2036         return hashlen_create(end_name_hash(hash), len);
2037 }
2038 EXPORT_SYMBOL(hashlen_string);
2039 
2040 /*
2041  * We know there's a real path component here of at least
2042  * one character.
2043  */
2044 static inline u64 hash_name(const void *salt, const char *name)
2045 {
2046         unsigned long hash = init_name_hash(salt);
2047         unsigned long len = 0, c;
2048 
2049         c = (unsigned char)*name;
2050         do {
2051                 len++;
2052                 hash = partial_name_hash(c, hash);
2053                 c = (unsigned char)name[len];
2054         } while (c && c != '/');
2055         return hashlen_create(end_name_hash(hash), len);
2056 }
2057 
2058 #endif
2059 
2060 /*
2061  * Name resolution.
2062  * This is the basic name resolution function, turning a pathname into
2063  * the final dentry. We expect 'base' to be positive and a directory.
2064  *
2065  * Returns 0 and nd will have valid dentry and mnt on success.
2066  * Returns error and drops reference to input namei data on failure.
2067  */
2068 static int link_path_walk(const char *name, struct nameidata *nd)
2069 {
2070         int err;
2071 
2072         if (IS_ERR(name))
2073                 return PTR_ERR(name);
2074         while (*name=='/')
2075                 name++;
2076         if (!*name)
2077                 return 0;
2078 
2079         /* At this point we know we have a real path component. */
2080         for(;;) {
2081                 u64 hash_len;
2082                 int type;
2083 
2084                 err = may_lookup(nd);
2085                 if (err)
2086                         return err;
2087 
2088                 hash_len = hash_name(nd->path.dentry, name);
2089 
2090                 type = LAST_NORM;
2091                 if (name[0] == '.') switch (hashlen_len(hash_len)) {
2092                         case 2:
2093                                 if (name[1] == '.') {
2094                                         type = LAST_DOTDOT;
2095                                         nd->flags |= LOOKUP_JUMPED;
2096                                 }
2097                                 break;
2098                         case 1:
2099                                 type = LAST_DOT;
2100                 }
2101                 if (likely(type == LAST_NORM)) {
2102                         struct dentry *parent = nd->path.dentry;
2103                         nd->flags &= ~LOOKUP_JUMPED;
2104                         if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
2105                                 struct qstr this = { { .hash_len = hash_len }, .name = name };
2106                                 err = parent->d_op->d_hash(parent, &this);
2107                                 if (err < 0)
2108                                         return err;
2109                                 hash_len = this.hash_len;
2110                                 name = this.name;
2111                         }
2112                 }
2113 
2114                 nd->last.hash_len = hash_len;
2115                 nd->last.name = name;
2116                 nd->last_type = type;
2117 
2118                 name += hashlen_len(hash_len);
2119                 if (!*name)
2120                         goto OK;
2121                 /*
2122                  * If it wasn't NUL, we know it was '/'. Skip that
2123                  * slash, and continue until no more slashes.
2124                  */
2125                 do {
2126                         name++;
2127                 } while (unlikely(*name == '/'));
2128                 if (unlikely(!*name)) {
2129 OK:
2130                         /* pathname body, done */
2131                         if (!nd->depth)
2132                                 return 0;
2133                         name = nd->stack[nd->depth - 1].name;
2134                         /* trailing symlink, done */
2135                         if (!name)
2136                                 return 0;
2137                         /* last component of nested symlink */
2138                         err = walk_component(nd, WALK_FOLLOW);
2139                 } else {
2140                         /* not the last component */
2141                         err = walk_component(nd, WALK_FOLLOW | WALK_MORE);
2142                 }
2143                 if (err < 0)
2144                         return err;
2145 
2146                 if (err) {
2147                         const char *s = get_link(nd);
2148 
2149                         if (IS_ERR(s))
2150                                 return PTR_ERR(s);
2151                         err = 0;
2152                         if (unlikely(!s)) {
2153                                 /* jumped */
2154                                 put_link(nd);
2155                         } else {
2156                                 nd->stack[nd->depth - 1].name = name;
2157                                 name = s;
2158                                 continue;
2159                         }
2160                 }
2161                 if (unlikely(!d_can_lookup(nd->path.dentry))) {
2162                         if (nd->flags & LOOKUP_RCU) {
2163                                 if (unlazy_walk(nd))
2164                                         return -ECHILD;
2165                         }
2166                         return -ENOTDIR;
2167                 }
2168         }
2169 }
2170 
2171 /* must be paired with terminate_walk() */
2172 static const char *path_init(struct nameidata *nd, unsigned flags)
2173 {
2174         const char *s = nd->name->name;
2175 
2176         if (!*s)
2177                 flags &= ~LOOKUP_RCU;
2178         if (flags & LOOKUP_RCU)
2179                 rcu_read_lock();
2180 
2181         nd->last_type = LAST_ROOT; /* if there are only slashes... */
2182         nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
2183         nd->depth = 0;
2184         if (flags & LOOKUP_ROOT) {
2185                 struct dentry *root = nd->root.dentry;
2186                 struct inode *inode = root->d_inode;
2187                 if (*s && unlikely(!d_can_lookup(root)))
2188                         return ERR_PTR(-ENOTDIR);
2189                 nd->path = nd->root;
2190                 nd->inode = inode;
2191                 if (flags & LOOKUP_RCU) {
2192                         nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2193                         nd->root_seq = nd->seq;
2194                         nd->m_seq = read_seqbegin(&mount_lock);
2195                 } else {
2196                         path_get(&nd->path);
2197                 }
2198                 return s;
2199         }
2200 
2201         nd->root.mnt = NULL;
2202         nd->path.mnt = NULL;
2203         nd->path.dentry = NULL;
2204 
2205         nd->m_seq = read_seqbegin(&mount_lock);
2206         if (*s == '/') {
2207                 set_root(nd);
2208                 if (likely(!nd_jump_root(nd)))
2209                         return s;
2210                 return ERR_PTR(-ECHILD);
2211         } else if (nd->dfd == AT_FDCWD) {
2212                 if (flags & LOOKUP_RCU) {
2213                         struct fs_struct *fs = current->fs;
2214                         unsigned seq;
2215 
2216                         do {
2217                                 seq = read_seqcount_begin(&fs->seq);
2218                                 nd->path = fs->pwd;
2219                                 nd->inode = nd->path.dentry->d_inode;
2220                                 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2221                         } while (read_seqcount_retry(&fs->seq, seq));
2222                 } else {
2223                         get_fs_pwd(current->fs, &nd->path);
2224                         nd->inode = nd->path.dentry->d_inode;
2225                 }
2226                 return s;
2227         } else {
2228                 /* Caller must check execute permissions on the starting path component */
2229                 struct fd f = fdget_raw(nd->dfd);
2230                 struct dentry *dentry;
2231 
2232                 if (!f.file)
2233                         return ERR_PTR(-EBADF);
2234 
2235                 dentry = f.file->f_path.dentry;
2236 
2237                 if (*s && unlikely(!d_can_lookup(dentry))) {
2238                         fdput(f);
2239                         return ERR_PTR(-ENOTDIR);
2240                 }
2241 
2242                 nd->path = f.file->f_path;
2243                 if (flags & LOOKUP_RCU) {
2244                         nd->inode = nd->path.dentry->d_inode;
2245                         nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
2246                 } else {
2247                         path_get(&nd->path);
2248                         nd->inode = nd->path.dentry->d_inode;
2249                 }
2250                 fdput(f);
2251                 return s;
2252         }
2253 }
2254 
2255 static const char *trailing_symlink(struct nameidata *nd)
2256 {
2257         const char *s;
2258         int error = may_follow_link(nd);
2259         if (unlikely(error))
2260                 return ERR_PTR(error);
2261         nd->flags |= LOOKUP_PARENT;
2262         nd->stack[0].name = NULL;
2263         s = get_link(nd);
2264         return s ? s : "";
2265 }
2266 
2267 static inline int lookup_last(struct nameidata *nd)
2268 {
2269         if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
2270                 nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
2271 
2272         nd->flags &= ~LOOKUP_PARENT;
2273         return walk_component(nd, 0);
2274 }
2275 
2276 static int handle_lookup_down(struct nameidata *nd)
2277 {
2278         struct path path = nd->path;
2279         struct inode *inode = nd->inode;
2280         unsigned seq = nd->seq;
2281         int err;
2282 
2283         if (nd->flags & LOOKUP_RCU) {
2284                 /*
2285                  * don't bother with unlazy_walk on failure - we are
2286                  * at the very beginning of walk, so we lose nothing
2287                  * if we simply redo everything in non-RCU mode
2288                  */
2289                 if (unlikely(!__follow_mount_rcu(nd, &path, &inode, &seq)))
2290                         return -ECHILD;
2291         } else {
2292                 dget(path.dentry);
2293                 err = follow_managed(&path, nd);
2294                 if (unlikely(err < 0))
2295                         return err;
2296                 inode = d_backing_inode(path.dentry);
2297                 seq = 0;
2298         }
2299         path_to_nameidata(&path, nd);
2300         nd->inode = inode;
2301         nd->seq = seq;
2302         return 0;
2303 }
2304 
2305 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2306 static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
2307 {
2308         const char *s = path_init(nd, flags);
2309         int err;
2310 
2311         if (unlikely(flags & LOOKUP_DOWN) && !IS_ERR(s)) {
2312                 err = handle_lookup_down(nd);
2313                 if (unlikely(err < 0))
2314                         s = ERR_PTR(err);
2315         }
2316 
2317         while (!(err = link_path_walk(s, nd))
2318                 && ((err = lookup_last(nd)) > 0)) {
2319                 s = trailing_symlink(nd);
2320         }
2321         if (!err)
2322                 err = complete_walk(nd);
2323 
2324         if (!err && nd->flags & LOOKUP_DIRECTORY)
2325                 if (!d_can_lookup(nd->path.dentry))
2326                         err = -ENOTDIR;
2327         if (!err) {
2328                 *path = nd->path;
2329                 nd->path.mnt = NULL;
2330                 nd->path.dentry = NULL;
2331         }
2332         terminate_walk(nd);
2333         return err;
2334 }
2335 
2336 static int filename_lookup(int dfd, struct filename *name, unsigned flags,
2337                            struct path *path, struct path *root)
2338 {
2339         int retval;
2340         struct nameidata nd;
2341         if (IS_ERR(name))
2342                 return PTR_ERR(name);
2343         if (unlikely(root)) {
2344                 nd.root = *root;
2345                 flags |= LOOKUP_ROOT;
2346         }
2347         set_nameidata(&nd, dfd, name);
2348         retval = path_lookupat(&nd, flags | LOOKUP_RCU, path);
2349         if (unlikely(retval == -ECHILD))
2350                 retval = path_lookupat(&nd, flags, path);
2351         if (unlikely(retval == -ESTALE))
2352                 retval = path_lookupat(&nd, flags | LOOKUP_REVAL, path);
2353 
2354         if (likely(!retval))
2355                 audit_inode(name, path->dentry, flags & LOOKUP_PARENT);
2356         restore_nameidata();
2357         putname(name);
2358         return retval;
2359 }
2360 
2361 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2362 static int path_parentat(struct nameidata *nd, unsigned flags,
2363                                 struct path *parent)
2364 {
2365         const char *s = path_init(nd, flags);
2366         int err = link_path_walk(s, nd);
2367         if (!err)
2368                 err = complete_walk(nd);
2369         if (!err) {
2370                 *parent = nd->path;
2371                 nd->path.mnt = NULL;
2372                 nd->path.dentry = NULL;
2373         }
2374         terminate_walk(nd);
2375         return err;
2376 }
2377 
2378 static struct filename *filename_parentat(int dfd, struct filename *name,
2379                                 unsigned int flags, struct path *parent,
2380                                 struct qstr *last, int *type)
2381 {
2382         int retval;
2383         struct nameidata nd;
2384 
2385         if (IS_ERR(name))
2386                 return name;
2387         set_nameidata(&nd, dfd, name);
2388         retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
2389         if (unlikely(retval == -ECHILD))
2390                 retval = path_parentat(&nd, flags, parent);
2391         if (unlikely(retval == -ESTALE))
2392                 retval = path_parentat(&nd, flags | LOOKUP_REVAL, parent);
2393         if (likely(!retval)) {
2394                 *last = nd.last;
2395                 *type = nd.last_type;
2396                 audit_inode(name, parent->dentry, LOOKUP_PARENT);
2397         } else {
2398                 putname(name);
2399                 name = ERR_PTR(retval);
2400         }
2401         restore_nameidata();
2402         return name;
2403 }
2404 
2405 /* does lookup, returns the object with parent locked */
2406 struct dentry *kern_path_locked(const char *name, struct path *path)
2407 {
2408         struct filename *filename;
2409         struct dentry *d;
2410         struct qstr last;
2411         int type;
2412 
2413         filename = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
2414                                     &last, &type);
2415         if (IS_ERR(filename))
2416                 return ERR_CAST(filename);
2417         if (unlikely(type != LAST_NORM)) {
2418                 path_put(path);
2419                 putname(filename);
2420                 return ERR_PTR(-EINVAL);
2421         }
2422         inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
2423         d = __lookup_hash(&last, path->dentry, 0);
2424         if (IS_ERR(d)) {
2425                 inode_unlock(path->dentry->d_inode);
2426                 path_put(path);
2427         }
2428         putname(filename);
2429         return d;
2430 }
2431 
2432 int kern_path(const char *name, unsigned int flags, struct path *path)
2433 {
2434         return filename_lookup(AT_FDCWD, getname_kernel(name),
2435                                flags, path, NULL);
2436 }
2437 EXPORT_SYMBOL(kern_path);
2438 
2439 /**
2440  * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
2441  * @dentry:  pointer to dentry of the base directory
2442  * @mnt: pointer to vfs mount of the base directory
2443  * @name: pointer to file name
2444  * @flags: lookup flags
2445  * @path: pointer to struct path to fill
2446  */
2447 int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
2448                     const char *name, unsigned int flags,
2449                     struct path *path)
2450 {
2451         struct path root = {.mnt = mnt, .dentry = dentry};
2452         /* the first argument of filename_lookup() is ignored with root */
2453         return filename_lookup(AT_FDCWD, getname_kernel(name),
2454                                flags , path, &root);
2455 }
2456 EXPORT_SYMBOL(vfs_path_lookup);
2457 
2458 static int lookup_one_len_common(const char *name, struct dentry *base,
2459                                  int len, struct qstr *this)
2460 {
2461         this->name = name;
2462         this->len = len;
2463         this->hash = full_name_hash(base, name, len);
2464         if (!len)
2465                 return -EACCES;
2466 
2467         if (unlikely(name[0] == '.')) {
2468                 if (len < 2 || (len == 2 && name[1] == '.'))
2469                         return -EACCES;
2470         }
2471 
2472         while (len--) {
2473                 unsigned int c = *(const unsigned char *)name++;
2474                 if (c == '/' || c == '\0')
2475                         return -EACCES;
2476         }
2477         /*
2478          * See if the low-level filesystem might want
2479          * to use its own hash..
2480          */
2481         if (base->d_flags & DCACHE_OP_HASH) {
2482                 int err = base->d_op->d_hash(base, this);
2483                 if (err < 0)
2484                         return err;
2485         }
2486 
2487         return inode_permission(base->d_inode, MAY_EXEC);
2488 }
2489 
2490 /**
2491  * try_lookup_one_len - filesystem helper to lookup single pathname component
2492  * @name:       pathname component to lookup
2493  * @base:       base directory to lookup from
2494  * @len:        maximum length @len should be interpreted to
2495  *
2496  * Look up a dentry by name in the dcache, returning NULL if it does not
2497  * currently exist.  The function does not try to create a dentry.
2498  *
2499  * Note that this routine is purely a helper for filesystem usage and should
2500  * not be called by generic code.
2501  *
2502  * The caller must hold base->i_mutex.
2503  */
2504 struct dentry *try_lookup_one_len(const char *name, struct dentry *base, int len)
2505 {
2506         struct qstr this;
2507         int err;
2508 
2509         WARN_ON_ONCE(!inode_is_locked(base->d_inode));
2510 
2511         err = lookup_one_len_common(name, base, len, &this);
2512         if (err)
2513                 return ERR_PTR(err);
2514 
2515         return lookup_dcache(&this, base, 0);
2516 }
2517 EXPORT_SYMBOL(try_lookup_one_len);
2518 
2519 /**
2520  * lookup_one_len - filesystem helper to lookup single pathname component
2521  * @name:       pathname component to lookup
2522  * @base:       base directory to lookup from
2523  * @len:        maximum length @len should be interpreted to
2524  *
2525  * Note that this routine is purely a helper for filesystem usage and should
2526  * not be called by generic code.
2527  *
2528  * The caller must hold base->i_mutex.
2529  */
2530 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
2531 {
2532         struct dentry *dentry;
2533         struct qstr this;
2534         int err;
2535 
2536         WARN_ON_ONCE(!inode_is_locked(base->d_inode));
2537 
2538         err = lookup_one_len_common(name, base, len, &this);
2539         if (err)
2540                 return ERR_PTR(err);
2541 
2542         dentry = lookup_dcache(&this, base, 0);
2543         return dentry ? dentry : __lookup_slow(&this, base, 0);
2544 }
2545 EXPORT_SYMBOL(lookup_one_len);
2546 
2547 /**
2548  * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
2549  * @name:       pathname component to lookup
2550  * @base:       base directory to lookup from
2551  * @len:        maximum length @len should be interpreted to
2552  *
2553  * Note that this routine is purely a helper for filesystem usage and should
2554  * not be called by generic code.
2555  *
2556  * Unlike lookup_one_len, it should be called without the parent
2557  * i_mutex held, and will take the i_mutex itself if necessary.
2558  */
2559 struct dentry *lookup_one_len_unlocked(const char *name,
2560                                        struct dentry *base, int len)
2561 {
2562         struct qstr this;
2563         int err;
2564         struct dentry *ret;
2565 
2566         err = lookup_one_len_common(name, base, len, &this);
2567         if (err)
2568                 return ERR_PTR(err);
2569 
2570         ret = lookup_dcache(&this, base, 0);
2571         if (!ret)
2572                 ret = lookup_slow(&this, base, 0);
2573         return ret;
2574 }
2575 EXPORT_SYMBOL(lookup_one_len_unlocked);
2576 
2577 #ifdef CONFIG_UNIX98_PTYS
2578 int path_pts(struct path *path)
2579 {
2580         /* Find something mounted on "pts" in the same directory as
2581          * the input path.
2582          */
2583         struct dentry *child, *parent;
2584         struct qstr this;
2585         int ret;
2586 
2587         ret = path_parent_directory(path);
2588         if (ret)
2589                 return ret;
2590 
2591         parent = path->dentry;
2592         this.name = "pts";
2593         this.len = 3;
2594         child = d_hash_and_lookup(parent, &this);
2595         if (!child)
2596                 return -ENOENT;
2597 
2598         path->dentry = child;
2599         dput(parent);
2600         follow_mount(path);
2601         return 0;
2602 }
2603 #endif
2604 
2605 int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
2606                  struct path *path, int *empty)
2607 {
2608         return filename_lookup(dfd, getname_flags(name, flags, empty),
2609                                flags, path, NULL);
2610 }
2611 EXPORT_SYMBOL(user_path_at_empty);
2612 
2613 /**
2614  * mountpoint_last - look up last component for umount
2615  * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"
2616  *
2617  * This is a special lookup_last function just for umount. In this case, we
2618  * need to resolve the path without doing any revalidation.
2619  *
2620  * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since
2621  * mountpoints are always pinned in the dcache, their ancestors are too. Thus,
2622  * in almost all cases, this lookup will be served out of the dcache. The only
2623  * cases where it won't are if nd->last refers to a symlink or the path is
2624  * bogus and it doesn't exist.
2625  *
2626  * Returns:
2627  * -error: if there was an error during lookup. This includes -ENOENT if the
2628  *         lookup found a negative dentry.
2629  *
2630  * 0:      if we successfully resolved nd->last and found it to not to be a
2631  *         symlink that needs to be followed.
2632  *
2633  * 1:      if we successfully resolved nd->last and found it to be a symlink
2634  *         that needs to be followed.
2635  */
2636 static int
2637 mountpoint_last(struct nameidata *nd)
2638 {
2639         int error = 0;
2640         struct dentry *dir = nd->path.dentry;
2641         struct path path;
2642 
2643         /* If we're in rcuwalk, drop out of it to handle last component */
2644         if (nd->flags & LOOKUP_RCU) {
2645                 if (unlazy_walk(nd))
2646                         return -ECHILD;
2647         }
2648 
2649         nd->flags &= ~LOOKUP_PARENT;
2650 
2651         if (unlikely(nd->last_type != LAST_NORM)) {
2652                 error = handle_dots(nd, nd->last_type);
2653                 if (error)
2654                         return error;
2655                 path.dentry = dget(nd->path.dentry);
2656         } else {
2657                 path.dentry = d_lookup(dir, &nd->last);
2658                 if (!path.dentry) {
2659                         /*
2660                          * No cached dentry. Mounted dentries are pinned in the
2661                          * cache, so that means that this dentry is probably
2662                          * a symlink or the path doesn't actually point
2663                          * to a mounted dentry.
2664                          */
2665                         path.dentry = lookup_slow(&nd->last, dir,
2666                                              nd->flags | LOOKUP_NO_REVAL);
2667                         if (IS_ERR(path.dentry))
2668                                 return PTR_ERR(path.dentry);
2669                 }
2670         }
2671         if (d_is_negative(path.dentry)) {
2672                 dput(path.dentry);
2673                 return -ENOENT;
2674         }
2675         path.mnt = nd->path.mnt;
2676         return step_into(nd, &path, 0, d_backing_inode(path.dentry), 0);
2677 }
2678 
2679 /**
2680  * path_mountpoint - look up a path to be umounted
2681  * @nd:         lookup context
2682  * @flags:      lookup flags
2683  * @path:       pointer to container for result
2684  *
2685  * Look up the given name, but don't attempt to revalidate the last component.
2686  * Returns 0 and "path" will be valid on success; Returns error otherwise.
2687  */
2688 static int
2689 path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path)
2690 {
2691         const char *s = path_init(nd, flags);
2692         int err;
2693 
2694         while (!(err = link_path_walk(s, nd)) &&
2695                 (err = mountpoint_last(nd)) > 0) {
2696                 s = trailing_symlink(nd);
2697         }
2698         if (!err) {
2699                 *path = nd->path;
2700                 nd->path.mnt = NULL;
2701                 nd->path.dentry = NULL;
2702                 follow_mount(path);
2703         }
2704         terminate_walk(nd);
2705         return err;
2706 }
2707 
2708 static int
2709 filename_mountpoint(int dfd, struct filename *name, struct path *path,
2710                         unsigned int flags)
2711 {
2712         struct nameidata nd;
2713         int error;
2714         if (IS_ERR(name))
2715                 return PTR_ERR(name);
2716         set_nameidata(&nd, dfd, name);
2717         error = path_mountpoint(&nd, flags | LOOKUP_RCU, path);
2718         if (unlikely(error == -ECHILD))
2719                 error = path_mountpoint(&nd, flags, path);
2720         if (unlikely(error == -ESTALE))
2721                 error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
2722         if (likely(!error))
2723                 audit_inode(name, path->dentry, 0);
2724         restore_nameidata();
2725         putname(name);
2726         return error;
2727 }
2728 
2729 /**
2730  * user_path_mountpoint_at - lookup a path from userland in order to umount it
2731  * @dfd:        directory file descriptor
2732  * @name:       pathname from userland
2733  * @flags:      lookup flags
2734  * @path:       pointer to container to hold result
2735  *
2736  * A umount is a special case for path walking. We're not actually interested
2737  * in the inode in this situation, and ESTALE errors can be a problem. We
2738  * simply want track down the dentry and vfsmount attached at the mountpoint
2739  * and avoid revalidating the last component.
2740  *
2741  * Returns 0 and populates "path" on success.
2742  */
2743 int
2744 user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
2745                         struct path *path)
2746 {
2747         return filename_mountpoint(dfd, getname(name), path, flags);
2748 }
2749 
2750 int
2751 kern_path_mountpoint(int dfd, const char *name, struct path *path,
2752                         unsigned int flags)
2753 {
2754         return filename_mountpoint(dfd, getname_kernel(name), path, flags);
2755 }
2756 EXPORT_SYMBOL(kern_path_mountpoint);
2757 
2758 int __check_sticky(struct inode *dir, struct inode *inode)
2759 {
2760         kuid_t fsuid = current_fsuid();
2761 
2762         if (uid_eq(inode->i_uid, fsuid))
2763                 return 0;
2764         if (uid_eq(dir->i_uid, fsuid))
2765                 return 0;
2766         return !capable_wrt_inode_uidgid(inode, CAP_FOWNER);
2767 }
2768 EXPORT_SYMBOL(__check_sticky);
2769 
2770 /*
2771  *      Check whether we can remove a link victim from directory dir, check
2772  *  whether the type of victim is right.
2773  *  1. We can't do it if dir is read-only (done in permission())
2774  *  2. We should have write and exec permissions on dir
2775  *  3. We can't remove anything from append-only dir
2776  *  4. We can't do anything with immutable dir (done in permission())
2777  *  5. If the sticky bit on dir is set we should either
2778  *      a. be owner of dir, or
2779  *      b. be owner of victim, or
2780  *      c. have CAP_FOWNER capability
2781  *  6. If the victim is append-only or immutable we can't do antyhing with
2782  *     links pointing to it.
2783  *  7. If the victim has an unknown uid or gid we can't change the inode.
2784  *  8. If we were asked to remove a directory and victim isn't one - ENOTDIR.
2785  *  9. If we were asked to remove a non-directory and victim isn't one - EISDIR.
2786  * 10. We can't remove a root or mountpoint.
2787  * 11. We don't allow removal of NFS sillyrenamed files; it's handled by
2788  *     nfs_async_unlink().
2789  */
2790 static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
2791 {
2792         struct inode *inode = d_backing_inode(victim);
2793         int error;
2794 
2795         if (d_is_negative(victim))
2796                 return -ENOENT;
2797         BUG_ON(!inode);
2798 
2799         BUG_ON(victim->d_parent->d_inode != dir);
2800 
2801         /* Inode writeback is not safe when the uid or gid are invalid. */
2802         if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
2803                 return -EOVERFLOW;
2804 
2805         audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
2806 
2807         error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
2808         if (error)
2809                 return error;
2810         if (IS_APPEND(dir))
2811                 return -EPERM;
2812 
2813         if (check_sticky(dir, inode) || IS_APPEND(inode) ||
2814             IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) || HAS_UNMAPPED_ID(inode))
2815                 return -EPERM;
2816         if (isdir) {
2817                 if (!d_is_dir(victim))
2818                         return -ENOTDIR;
2819                 if (IS_ROOT(victim))
2820                         return -EBUSY;
2821         } else if (d_is_dir(victim))
2822                 return -EISDIR;
2823         if (IS_DEADDIR(dir))
2824                 return -ENOENT;
2825         if (victim->d_flags & DCACHE_NFSFS_RENAMED)
2826                 return -EBUSY;
2827         return 0;
2828 }
2829 
2830 /*      Check whether we can create an object with dentry child in directory
2831  *  dir.
2832  *  1. We can't do it if child already exists (open has special treatment for
2833  *     this case, but since we are inlined it's OK)
2834  *  2. We can't do it if dir is read-only (done in permission())
2835  *  3. We can't do it if the fs can't represent the fsuid or fsgid.
2836  *  4. We should have write and exec permissions on dir
2837  *  5. We can't do it if dir is immutable (done in permission())
2838  */
2839 static inline int may_create(struct inode *dir, struct dentry *child)
2840 {
2841         struct user_namespace *s_user_ns;
2842         audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
2843         if (child->d_inode)
2844                 return -EEXIST;
2845         if (IS_DEADDIR(dir))
2846                 return -ENOENT;
2847         s_user_ns = dir->i_sb->s_user_ns;
2848         if (!kuid_has_mapping(s_user_ns, current_fsuid()) ||
2849             !kgid_has_mapping(s_user_ns, current_fsgid()))
2850                 return -EOVERFLOW;
2851         return inode_permission(dir, MAY_WRITE | MAY_EXEC);
2852 }
2853 
2854 /*
2855  * p1 and p2 should be directories on the same fs.
2856  */
2857 struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
2858 {
2859         struct dentry *p;
2860 
2861         if (p1 == p2) {
2862                 inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2863                 return NULL;
2864         }
2865 
2866         mutex_lock(&p1->d_sb->s_vfs_rename_mutex);
2867 
2868         p = d_ancestor(p2, p1);
2869         if (p) {
2870                 inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
2871                 inode_lock_nested(p1->d_inode, I_MUTEX_CHILD);
2872                 return p;
2873         }
2874 
2875         p = d_ancestor(p1, p2);
2876         if (p) {
2877                 inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2878                 inode_lock_nested(p2->d_inode, I_MUTEX_CHILD);
2879                 return p;
2880         }
2881 
2882         inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2883         inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2);
2884         return NULL;
2885 }
2886 EXPORT_SYMBOL(lock_rename);
2887 
2888 void unlock_rename(struct dentry *p1, struct dentry *p2)
2889 {
2890         inode_unlock(p1->d_inode);
2891         if (p1 != p2) {
2892                 inode_unlock(p2->d_inode);
2893                 mutex_unlock(&p1->d_sb->s_vfs_rename_mutex);
2894         }
2895 }
2896 EXPORT_SYMBOL(unlock_rename);
2897 
2898 int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
2899                 bool want_excl)
2900 {
2901         int error = may_create(dir, dentry);
2902         if (error)
2903                 return error;
2904 
2905         if (!dir->i_op->create)
2906                 return -EACCES; /* shouldn't it be ENOSYS? */
2907         mode &= S_IALLUGO;
2908         mode |= S_IFREG;
2909         error = security_inode_create(dir, dentry, mode);
2910         if (error)
2911                 return error;
2912         error = dir->i_op->create(dir, dentry, mode, want_excl);
2913         if (!error)
2914                 fsnotify_create(dir, dentry);
2915         return error;
2916 }
2917 EXPORT_SYMBOL(vfs_create);
2918 
2919 int vfs_mkobj(struct dentry *dentry, umode_t mode,
2920                 int (*f)(struct dentry *, umode_t, void *),
2921                 void *arg)
2922 {
2923         struct inode *dir = dentry->d_parent->d_inode;
2924         int error = may_create(dir, dentry);
2925         if (error)
2926                 return error;
2927 
2928         mode &= S_IALLUGO;
2929         mode |= S_IFREG;
2930         error = security_inode_create(dir, dentry, mode);
2931         if (error)
2932                 return error;
2933         error = f(dentry, mode, arg);
2934         if (!error)
2935                 fsnotify_create(dir, dentry);
2936         return error;
2937 }
2938 EXPORT_SYMBOL(vfs_mkobj);
2939 
2940 bool may_open_dev(const struct path *path)
2941 {
2942         return !(path->mnt->mnt_flags & MNT_NODEV) &&
2943                 !(path->mnt->mnt_sb->s_iflags & SB_I_NODEV);
2944 }
2945 
2946 static int may_open(const struct path *path, int acc_mode, int flag)
2947 {
2948         struct dentry *dentry = path->dentry;
2949         struct inode *inode = dentry->d_inode;
2950         int error;
2951 
2952         if (!inode)
2953                 return -ENOENT;
2954 
2955         switch (inode->i_mode & S_IFMT) {
2956         case S_IFLNK:
2957                 return -ELOOP;
2958         case S_IFDIR:
2959                 if (acc_mode & MAY_WRITE)
2960                         return -EISDIR;
2961                 break;
2962         case S_IFBLK:
2963         case S_IFCHR:
2964                 if (!may_open_dev(path))
2965                         return -EACCES;
2966                 /*FALLTHRU*/
2967         case S_IFIFO:
2968         case S_IFSOCK:
2969                 flag &= ~O_TRUNC;
2970                 break;
2971         }
2972 
2973         error = inode_permission(inode, MAY_OPEN | acc_mode);
2974         if (error)
2975                 return error;
2976 
2977         /*
2978          * An append-only file must be opened in append mode for writing.
2979          */
2980         if (IS_APPEND(inode)) {
2981                 if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
2982                         return -EPERM;
2983                 if (flag & O_TRUNC)
2984                         return -EPERM;
2985         }
2986 
2987         /* O_NOATIME can only be set by the owner or superuser */
2988         if (flag & O_NOATIME && !inode_owner_or_capable(inode))
2989                 return -EPERM;
2990 
2991         return 0;
2992 }
2993 
2994 static int handle_truncate(struct file *filp)
2995 {
2996         const struct path *path = &filp->f_path;
2997         struct inode *inode = path->dentry->d_inode;
2998         int error = get_write_access(inode);
2999         if (error)
3000                 return error;
3001         /*
3002          * Refuse to truncate files with mandatory locks held on them.
3003          */
3004         error = locks_verify_locked(filp);
3005         if (!error)
3006                 error = security_path_truncate(path);
3007         if (!error) {
3008                 error = do_truncate(path->dentry, 0,
3009                                     ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
3010                                     filp);
3011         }
3012         put_write_access(inode);
3013         return error;
3014 }
3015 
3016 static inline int open_to_namei_flags(int flag)
3017 {
3018         if ((flag & O_ACCMODE) == 3)
3019                 flag--;
3020         return flag;
3021 }
3022 
3023 static int may_o_create(const struct path *dir, struct dentry *dentry, umode_t mode)
3024 {
3025         struct user_namespace *s_user_ns;
3026         int error = security_path_mknod(dir, dentry, mode, 0);
3027         if (error)
3028                 return error;
3029 
3030         s_user_ns = dir->dentry->d_sb->s_user_ns;
3031         if (!kuid_has_mapping(s_user_ns, current_fsuid()) ||
3032             !kgid_has_mapping(s_user_ns, current_fsgid()))
3033                 return -EOVERFLOW;
3034 
3035         error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC);
3036         if (error)
3037                 return error;
3038 
3039         return security_inode_create(dir->dentry->d_inode, dentry, mode);
3040 }
3041 
3042 /*
3043  * Attempt to atomically look up, create and open a file from a negative
3044  * dentry.
3045  *
3046  * Returns 0 if successful.  The file will have been created and attached to
3047  * @file by the filesystem calling finish_open().
3048  *
3049  * If the file was looked up only or didn't need creating, FMODE_OPENED won't
3050  * be set.  The caller will need to perform the open themselves.  @path will
3051  * have been updated to point to the new dentry.  This may be negative.
3052  *
3053  * Returns an error code otherwise.
3054  */
3055 static int atomic_open(struct nameidata *nd, struct dentry *dentry,
3056                         struct path *path, struct file *file,
3057                         const struct open_flags *op,
3058                         int open_flag, umode_t mode)
3059 {
3060         struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
3061         struct inode *dir =  nd->path.dentry->d_inode;
3062         int error;
3063 
3064         if (!(~open_flag & (O_EXCL | O_CREAT))) /* both O_EXCL and O_CREAT */
3065                 open_flag &= ~O_TRUNC;
3066 
3067         if (nd->flags & LOOKUP_DIRECTORY)
3068                 open_flag |= O_DIRECTORY;
3069 
3070         file->f_path.dentry = DENTRY_NOT_SET;
3071         file->f_path.mnt = nd->path.mnt;
3072         error = dir->i_op->atomic_open(dir, dentry, file,
3073                                        open_to_namei_flags(open_flag), mode);
3074         d_lookup_done(dentry);
3075         if (!error) {
3076                 if (file->f_mode & FMODE_OPENED) {
3077                         /*
3078                          * We didn't have the inode before the open, so check open
3079                          * permission here.
3080                          */
3081                         int acc_mode = op->acc_mode;
3082                         if (file->f_mode & FMODE_CREATED) {
3083                                 WARN_ON(!(open_flag & O_CREAT));
3084                                 fsnotify_create(dir, dentry);
3085                                 acc_mode = 0;
3086                         }
3087                         error = may_open(&file->f_path, acc_mode, open_flag);
3088                         if (WARN_ON(error > 0))
3089                                 error = -EINVAL;
3090                 } else if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
3091                         error = -EIO;
3092                 } else {
3093                         if (file->f_path.dentry) {
3094                                 dput(dentry);
3095                                 dentry = file->f_path.dentry;
3096                         }
3097                         if (file->f_mode & FMODE_CREATED)
3098                                 fsnotify_create(dir, dentry);
3099                         if (unlikely(d_is_negative(dentry))) {
3100                                 error = -ENOENT;
3101                         } else {
3102                                 path->dentry = dentry;
3103                                 path->mnt = nd->path.mnt;
3104                                 return 0;
3105                         }
3106                 }
3107         }
3108         dput(dentry);
3109         return error;
3110 }
3111 
3112 /*
3113  * Look up and maybe create and open the last component.
3114  *
3115  * Must be called with parent locked (exclusive in O_CREAT case).
3116  *
3117  * Returns 0 on success, that is, if
3118  *  the file was successfully atomically created (if necessary) and opened, or
3119  *  the file was not completely opened at this time, though lookups and
3120  *  creations were performed.
3121  * These case are distinguished by presence of FMODE_OPENED on file->f_mode.
3122  * In the latter case dentry returned in @path might be negative if O_CREAT
3123  * hadn't been specified.
3124  *
3125  * An error code is returned on failure.
3126  */
3127 static int lookup_open(struct nameidata *nd, struct path *path,
3128                         struct file *file,
3129                         const struct open_flags *op,
3130                         bool got_write)
3131 {
3132         struct dentry *dir = nd->path.dentry;
3133         struct inode *dir_inode = dir->d_inode;
3134         int open_flag = op->open_flag;
3135         struct dentry *dentry;
3136         int error, create_error = 0;
3137         umode_t mode = op->mode;
3138         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
3139 
3140         if (unlikely(IS_DEADDIR(dir_inode)))
3141                 return -ENOENT;
3142 
3143         file->f_mode &= ~FMODE_CREATED;
3144         dentry = d_lookup(dir, &nd->last);
3145         for (;;) {
3146                 if (!dentry) {
3147                         dentry = d_alloc_parallel(dir, &nd->last, &wq);
3148                         if (IS_ERR(dentry))
3149                                 return PTR_ERR(dentry);
3150                 }
3151                 if (d_in_lookup(dentry))
3152                         break;
3153 
3154                 error = d_revalidate(dentry, nd->flags);
3155                 if (likely(error > 0))
3156                         break;
3157                 if (error)
3158                         goto out_dput;
3159                 d_invalidate(dentry);
3160                 dput(dentry);
3161                 dentry = NULL;
3162         }
3163         if (dentry->d_inode) {
3164                 /* Cached positive dentry: will open in f_op->open */
3165                 goto out_no_open;
3166         }
3167 
3168         /*
3169          * Checking write permission is tricky, bacuse we don't know if we are
3170          * going to actually need it: O_CREAT opens should work as long as the
3171          * file exists.  But checking existence breaks atomicity.  The trick is
3172          * to check access and if not granted clear O_CREAT from the flags.
3173          *
3174          * Another problem is returing the "right" error value (e.g. for an
3175          * O_EXCL open we want to return EEXIST not EROFS).
3176          */
3177         if (open_flag & O_CREAT) {
3178                 if (!IS_POSIXACL(dir->d_inode))
3179                         mode &= ~current_umask();
3180                 if (unlikely(!got_write)) {
3181                         create_error = -EROFS;
3182                         open_flag &= ~O_CREAT;
3183                         if (open_flag & (O_EXCL | O_TRUNC))
3184                                 goto no_open;
3185                         /* No side effects, safe to clear O_CREAT */
3186                 } else {
3187                         create_error = may_o_create(&nd->path, dentry, mode);
3188                         if (create_error) {
3189                                 open_flag &= ~O_CREAT;
3190                                 if (open_flag & O_EXCL)
3191                                         goto no_open;
3192                         }
3193                 }
3194         } else if ((open_flag & (O_TRUNC|O_WRONLY|O_RDWR)) &&
3195                    unlikely(!got_write)) {
3196                 /*
3197                  * No O_CREATE -> atomicity not a requirement -> fall
3198                  * back to lookup + open
3199                  */
3200                 goto no_open;
3201         }
3202 
3203         if (dir_inode->i_op->atomic_open) {
3204                 error = atomic_open(nd, dentry, path, file, op, open_flag,
3205                                     mode);
3206                 if (unlikely(error == -ENOENT) && create_error)
3207                         error = create_error;
3208                 return error;
3209         }
3210 
3211 no_open:
3212         if (d_in_lookup(dentry)) {
3213                 struct dentry *res = dir_inode->i_op->lookup(dir_inode, dentry,
3214                                                              nd->flags);
3215                 d_lookup_done(dentry);
3216                 if (unlikely(res)) {
3217                         if (IS_ERR(res)) {
3218                                 error = PTR_ERR(res);
3219                                 goto out_dput;
3220                         }
3221                         dput(dentry);
3222                         dentry = res;
3223                 }
3224         }
3225 
3226         /* Negative dentry, just create the file */
3227         if (!dentry->d_inode && (open_flag & O_CREAT)) {
3228                 file->f_mode |= FMODE_CREATED;
3229                 audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
3230                 if (!dir_inode->i_op->create) {
3231                         error = -EACCES;
3232                         goto out_dput;
3233                 }
3234                 error = dir_inode->i_op->create(dir_inode, dentry, mode,
3235                                                 open_flag & O_EXCL);
3236                 if (error)
3237                         goto out_dput;
3238                 fsnotify_create(dir_inode, dentry);
3239         }
3240         if (unlikely(create_error) && !dentry->d_inode) {
3241                 error = create_error;
3242                 goto out_dput;
3243         }
3244 out_no_open:
3245         path->dentry = dentry;
3246         path->mnt = nd->path.mnt;
3247         return 0;
3248 
3249 out_dput:
3250         dput(dentry);
3251         return error;
3252 }
3253 
3254 /*
3255  * Handle the last step of open()
3256  */
3257 static int do_last(struct nameidata *nd,
3258                    struct file *file, const struct open_flags *op)
3259 {
3260         struct dentry *dir = nd->path.dentry;
3261         int open_flag = op->open_flag;
3262         bool will_truncate = (open_flag & O_TRUNC) != 0;
3263         bool got_write = false;
3264         int acc_mode = op->acc_mode;
3265         unsigned seq;
3266         struct inode *inode;
3267         struct path path;
3268         int error;
3269 
3270         nd->flags &= ~LOOKUP_PARENT;
3271         nd->flags |= op->intent;
3272 
3273         if (nd->last_type != LAST_NORM) {
3274                 error = handle_dots(nd, nd->last_type);
3275                 if (unlikely(error))
3276                         return error;
3277                 goto finish_open;
3278         }
3279 
3280         if (!(open_flag & O_CREAT)) {
3281                 if (nd->last.name[nd->last.len])
3282                         nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
3283                 /* we _can_ be in RCU mode here */
3284                 error = lookup_fast(nd, &path, &inode, &seq);
3285                 if (likely(error > 0))
3286                         goto finish_lookup;
3287 
3288                 if (error < 0)
3289                         return error;
3290 
3291                 BUG_ON(nd->inode != dir->d_inode);
3292                 BUG_ON(nd->flags & LOOKUP_RCU);
3293         } else {
3294                 /* create side of things */
3295                 /*
3296                  * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED
3297                  * has been cleared when we got to the last component we are
3298                  * about to look up
3299                  */
3300                 error = complete_walk(nd);
3301                 if (error)
3302                         return error;
3303 
3304                 audit_inode(nd->name, dir, LOOKUP_PARENT);
3305                 /* trailing slashes? */
3306                 if (unlikely(nd->last.name[nd->last.len]))
3307                         return -EISDIR;
3308         }
3309 
3310         if (open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
3311                 error = mnt_want_write(nd->path.mnt);
3312                 if (!error)
3313                         got_write = true;
3314                 /*
3315                  * do _not_ fail yet - we might not need that or fail with
3316                  * a different error; let lookup_open() decide; we'll be
3317                  * dropping this one anyway.
3318                  */
3319         }
3320         if (open_flag & O_CREAT)
3321                 inode_lock(dir->d_inode);
3322         else
3323                 inode_lock_shared(dir->d_inode);
3324         error = lookup_open(nd, &path, file, op, got_write);
3325         if (open_flag & O_CREAT)
3326                 inode_unlock(dir->d_inode);
3327         else
3328                 inode_unlock_shared(dir->d_inode);
3329 
3330         if (error)
3331                 goto out;
3332 
3333         if (file->f_mode & FMODE_OPENED) {
3334                 if ((file->f_mode & FMODE_CREATED) ||
3335                     !S_ISREG(file_inode(file)->i_mode))
3336                         will_truncate = false;
3337 
3338                 audit_inode(nd->name, file->f_path.dentry, 0);
3339                 goto opened;
3340         }
3341 
3342         if (file->f_mode & FMODE_CREATED) {
3343                 /* Don't check for write permission, don't truncate */
3344                 open_flag &= ~O_TRUNC;
3345                 will_truncate = false;
3346                 acc_mode = 0;
3347                 path_to_nameidata(&path, nd);
3348                 goto finish_open_created;
3349         }
3350 
3351         /*
3352          * If atomic_open() acquired write access it is dropped now due to
3353          * possible mount and symlink following (this might be optimized away if
3354          * necessary...)
3355          */
3356         if (got_write) {
3357                 mnt_drop_write(nd->path.mnt);
3358                 got_write = false;
3359         }
3360 
3361         error = follow_managed(&path, nd);
3362         if (unlikely(error < 0))
3363                 return error;
3364 
3365         if (unlikely(d_is_negative(path.dentry))) {
3366                 path_to_nameidata(&path, nd);
3367                 return -ENOENT;
3368         }
3369 
3370         /*
3371          * create/update audit record if it already exists.
3372          */
3373         audit_inode(nd->name, path.dentry, 0);
3374 
3375         if (unlikely((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))) {
3376                 path_to_nameidata(&path, nd);
3377                 return -EEXIST;
3378         }
3379 
3380         seq = 0;        /* out of RCU mode, so the value doesn't matter */
3381         inode = d_backing_inode(path.dentry);
3382 finish_lookup:
3383         error = step_into(nd, &path, 0, inode, seq);
3384         if (unlikely(error))
3385                 return error;
3386 finish_open:
3387         /* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
3388         error = complete_walk(nd);
3389         if (error)
3390                 return error;
3391         audit_inode(nd->name, nd->path.dentry, 0);
3392         if (open_flag & O_CREAT) {
3393                 error = -EISDIR;
3394                 if (d_is_dir(nd->path.dentry))
3395                         goto out;
3396                 error = may_create_in_sticky(dir,
3397                                              d_backing_inode(nd->path.dentry));
3398                 if (unlikely(error))
3399                         goto out;
3400         }
3401         error = -ENOTDIR;
3402         if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
3403                 goto out;
3404         if (!d_is_reg(nd->path.dentry))
3405                 will_truncate = false;
3406 
3407         if (will_truncate) {
3408                 error = mnt_want_write(nd->path.mnt);
3409                 if (error)
3410                         goto out;
3411                 got_write = true;
3412         }
3413 finish_open_created:
3414         error = may_open(&nd->path, acc_mode, open_flag);
3415         if (error)
3416                 goto out;
3417         BUG_ON(file->f_mode & FMODE_OPENED); /* once it's opened, it's opened */
3418         error = vfs_open(&nd->path, file);
3419         if (error)
3420                 goto out;
3421 opened:
3422         error = ima_file_check(file, op->acc_mode);
3423         if (!error && will_truncate)
3424                 error = handle_truncate(file);
3425 out:
3426         if (unlikely(error > 0)) {
3427                 WARN_ON(1);
3428                 error = -EINVAL;
3429         }
3430         if (got_write)
3431                 mnt_drop_write(nd->path.mnt);
3432         return error;
3433 }
3434 
3435 struct dentry *vfs_tmpfile(struct dentry *dentry, umode_t mode, int open_flag)
3436 {
3437         struct dentry *child = NULL;
3438         struct inode *dir = dentry->d_inode;
3439         struct inode *inode;
3440         int error;
3441 
3442         /* we want directory to be writable */
3443         error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
3444         if (error)
3445                 goto out_err;
3446         error = -EOPNOTSUPP;
3447         if (!dir->i_op->tmpfile)
3448                 goto out_err;
3449         error = -ENOMEM;
3450         child = d_alloc(dentry, &slash_name);
3451         if (unlikely(!child))
3452                 goto out_err;
3453         error = dir->i_op->tmpfile(dir, child, mode);
3454         if (error)
3455                 goto out_err;
3456         error = -ENOENT;
3457         inode = child->d_inode;
3458         if (unlikely(!inode))
3459                 goto out_err;
3460         if (!(open_flag & O_EXCL)) {
3461                 spin_lock(&inode->i_lock);
3462                 inode->i_state |= I_LINKABLE;
3463                 spin_unlock(&inode->i_lock);
3464         }
3465         return child;
3466 
3467 out_err:
3468         dput(child);
3469         return ERR_PTR(error);
3470 }
3471 EXPORT_SYMBOL(vfs_tmpfile);
3472 
3473 static int do_tmpfile(struct nameidata *nd, unsigned flags,
3474                 const struct open_flags *op,
3475                 struct file *file)
3476 {
3477         struct dentry *child;
3478         struct path path;
3479         int error = path_lookupat(nd, flags | LOOKUP_DIRECTORY, &path);
3480         if (unlikely(error))
3481                 return error;
3482         error = mnt_want_write(path.mnt);
3483         if (unlikely(error))
3484                 goto out;
3485         child = vfs_tmpfile(path.dentry, op->mode, op->open_flag);
3486         error = PTR_ERR(child);
3487         if (IS_ERR(child))
3488                 goto out2;
3489         dput(path.dentry);
3490         path.dentry = child;
3491         audit_inode(nd->name, child, 0);
3492         /* Don't check for other permissions, the inode was just created */
3493         error = may_open(&path, 0, op->open_flag);
3494         if (error)
3495                 goto out2;
3496         file->f_path.mnt = path.mnt;
3497         error = finish_open(file, child, NULL);
3498 out2:
3499         mnt_drop_write(path.mnt);
3500 out:
3501         path_put(&path);
3502         return error;
3503 }
3504 
3505 static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file)
3506 {
3507         struct path path;
3508         int error = path_lookupat(nd, flags, &path);
3509         if (!error) {
3510                 audit_inode(nd->name, path.dentry, 0);
3511                 error = vfs_open(&path, file);
3512                 path_put(&path);
3513         }
3514         return error;
3515 }
3516 
3517 static struct file *path_openat(struct nameidata *nd,
3518                         const struct open_flags *op, unsigned flags)
3519 {
3520         struct file *file;
3521         int error;
3522 
3523         file = alloc_empty_file(op->open_flag, current_cred());
3524         if (IS_ERR(file))
3525                 return file;
3526 
3527         if (unlikely(file->f_flags & __O_TMPFILE)) {
3528                 error = do_tmpfile(nd, flags, op, file);
3529         } else if (unlikely(file->f_flags & O_PATH)) {
3530                 error = do_o_path(nd, flags, file);
3531         } else {
3532                 const char *s = path_init(nd, flags);
3533                 while (!(error = link_path_walk(s, nd)) &&
3534                         (error = do_last(nd, file, op)) > 0) {
3535                         nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
3536                         s = trailing_symlink(nd);
3537                 }
3538                 terminate_walk(nd);
3539         }
3540         if (likely(!error)) {
3541                 if (likely(file->f_mode & FMODE_OPENED))
3542                         return file;
3543                 WARN_ON(1);
3544                 error = -EINVAL;
3545         }
3546         fput(file);
3547         if (error == -EOPENSTALE) {
3548                 if (flags & LOOKUP_RCU)
3549                         error = -ECHILD;
3550                 else
3551                         error = -ESTALE;
3552         }
3553         return ERR_PTR(error);
3554 }
3555 
3556 struct file *do_filp_open(int dfd, struct filename *pathname,
3557                 const struct open_flags *op)
3558 {
3559         struct nameidata nd;
3560         int flags = op->lookup_flags;
3561         struct file *filp;
3562 
3563         set_nameidata(&nd, dfd, pathname);
3564         filp = path_openat(&nd, op, flags | LOOKUP_RCU);
3565         if (unlikely(filp == ERR_PTR(-ECHILD)))
3566                 filp = path_openat(&nd, op, flags);
3567         if (unlikely(filp == ERR_PTR(-ESTALE)))
3568                 filp = path_openat(&nd, op, flags | LOOKUP_REVAL);
3569         restore_nameidata();
3570         return filp;
3571 }
3572 
3573 struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
3574                 const char *name, const struct open_flags *op)
3575 {
3576         struct nameidata nd;
3577         struct file *file;
3578         struct filename *filename;
3579         int flags = op->lookup_flags | LOOKUP_ROOT;
3580 
3581         nd.root.mnt = mnt;
3582         nd.root.dentry = dentry;
3583 
3584         if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
3585                 return ERR_PTR(-ELOOP);
3586 
3587         filename = getname_kernel(name);
3588         if (IS_ERR(filename))
3589                 return ERR_CAST(filename);
3590 
3591         set_nameidata(&nd, -1, filename);
3592         file = path_openat(&nd, op, flags | LOOKUP_RCU);
3593         if (unlikely(file == ERR_PTR(-ECHILD)))
3594                 file = path_openat(&nd, op, flags);
3595         if (unlikely(file == ERR_PTR(-ESTALE)))
3596                 file = path_openat(&nd, op, flags | LOOKUP_REVAL);
3597         restore_nameidata();
3598         putname(filename);
3599         return file;
3600 }
3601 
3602 static struct dentry *filename_create(int dfd, struct filename *name,
3603                                 struct path *path, unsigned int lookup_flags)
3604 {
3605         struct dentry *dentry = ERR_PTR(-EEXIST);
3606         struct qstr last;
3607         int type;
3608         int err2;
3609         int error;
3610         bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
3611 
3612         /*
3613          * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
3614          * other flags passed in are ignored!
3615          */
3616         lookup_flags &= LOOKUP_REVAL;
3617 
3618         name = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
3619         if (IS_ERR(name))
3620                 return ERR_CAST(name);
3621 
3622         /*
3623          * Yucky last component or no last component at all?
3624          * (foo/., foo/.., /////)
3625          */
3626         if (unlikely(type != LAST_NORM))
3627                 goto out;
3628 
3629         /* don't fail immediately if it's r/o, at least try to report other errors */
3630         err2 = mnt_want_write(path->mnt);
3631         /*
3632          * Do the final lookup.
3633          */
3634         lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;
3635         inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
3636         dentry = __lookup_hash(&last, path->dentry, lookup_flags);
3637         if (IS_ERR(dentry))
3638                 goto unlock;
3639 
3640         error = -EEXIST;
3641         if (d_is_positive(dentry))
3642                 goto fail;
3643 
3644         /*
3645          * Special case - lookup gave negative, but... we had foo/bar/
3646          * From the vfs_mknod() POV we just have a negative dentry -
3647          * all is fine. Let's be bastards - you had / on the end, you've
3648          * been asking for (non-existent) directory. -ENOENT for you.
3649          */
3650         if (unlikely(!is_dir && last.name[last.len])) {
3651                 error = -ENOENT;
3652                 goto fail;
3653         }
3654         if (unlikely(err2)) {
3655                 error = err2;
3656                 goto fail;
3657         }
3658         putname(name);
3659         return dentry;
3660 fail:
3661         dput(dentry);
3662         dentry = ERR_PTR(error);
3663 unlock:
3664         inode_unlock(path->dentry->d_inode);
3665         if (!err2)
3666                 mnt_drop_write(path->mnt);
3667 out:
3668         path_put(path);
3669         putname(name);
3670         return dentry;
3671 }
3672 
3673 struct dentry *kern_path_create(int dfd, const char *pathname,
3674                                 struct path *path, unsigned int lookup_flags)
3675 {
3676         return filename_create(dfd, getname_kernel(pathname),
3677                                 path, lookup_flags);
3678 }
3679 EXPORT_SYMBOL(kern_path_create);
3680 
3681 void done_path_create(struct path *path, struct dentry *dentry)
3682 {
3683         dput(dentry);
3684         inode_unlock(path->dentry->d_inode);
3685         mnt_drop_write(path->mnt);
3686         path_put(path);
3687 }
3688 EXPORT_SYMBOL(done_path_create);
3689 
3690 inline struct dentry *user_path_create(int dfd, const char __user *pathname,
3691                                 struct path *path, unsigned int lookup_flags)
3692 {
3693         return filename_create(dfd, getname(pathname), path, lookup_flags);
3694 }
3695 EXPORT_SYMBOL(user_path_create);
3696 
3697 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
3698 {
3699         int error = may_create(dir, dentry);
3700 
3701         if (error)
3702                 return error;
3703 
3704         if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
3705                 return -EPERM;
3706 
3707         if (!dir->i_op->mknod)
3708                 return -EPERM;
3709 
3710         error = devcgroup_inode_mknod(mode, dev);
3711         if (error)
3712                 return error;
3713 
3714         error = security_inode_mknod(dir, dentry, mode, dev);
3715         if (error)
3716                 return error;
3717 
3718         error = dir->i_op->mknod(dir, dentry, mode, dev);
3719         if (!error)
3720                 fsnotify_create(dir, dentry);
3721         return error;
3722 }
3723 EXPORT_SYMBOL(vfs_mknod);
3724 
3725 static int may_mknod(umode_t mode)
3726 {
3727         switch (mode & S_IFMT) {
3728         case S_IFREG:
3729         case S_IFCHR:
3730         case S_IFBLK:
3731         case S_IFIFO:
3732         case S_IFSOCK:
3733         case 0: /* zero mode translates to S_IFREG */
3734                 return 0;
3735         case S_IFDIR:
3736                 return -EPERM;
3737         default:
3738                 return -EINVAL;
3739         }
3740 }
3741 
3742 long do_mknodat(int dfd, const char __user *filename, umode_t mode,
3743                 unsigned int dev)
3744 {
3745         struct dentry *dentry;
3746         struct path path;
3747         int error;
3748         unsigned int lookup_flags = 0;
3749 
3750         error = may_mknod(mode);
3751         if (error)
3752                 return error;
3753 retry:
3754         dentry = user_path_create(dfd, filename, &path, lookup_flags);
3755         if (IS_ERR(dentry))
3756                 return PTR_ERR(dentry);
3757 
3758         if (!IS_POSIXACL(path.dentry->d_inode))
3759                 mode &= ~current_umask();
3760         error = security_path_mknod(&path, dentry, mode, dev);
3761         if (error)
3762                 goto out;
3763         switch (mode & S_IFMT) {
3764                 case 0: case S_IFREG:
3765                         error = vfs_create(path.dentry->d_inode,dentry,mode,true);
3766                         if (!error)
3767                                 ima_post_path_mknod(dentry);
3768                         break;
3769                 case S_IFCHR: case S_IFBLK:
3770                         error = vfs_mknod(path.dentry->d_inode,dentry,mode,
3771                                         new_decode_dev(dev));
3772                         break;
3773                 case S_IFIFO: case S_IFSOCK:
3774                         error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
3775                         break;
3776         }
3777 out:
3778         done_path_create(&path, dentry);
3779         if (retry_estale(error, lookup_flags)) {
3780                 lookup_flags |= LOOKUP_REVAL;
3781                 goto retry;
3782         }
3783         return error;
3784 }
3785 
3786 SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
3787                 unsigned int, dev)
3788 {
3789         return do_mknodat(dfd, filename, mode, dev);
3790 }
3791 
3792 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
3793 {
3794         return do_mknodat(AT_FDCWD, filename, mode, dev);
3795 }
3796 
3797 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
3798 {
3799         int error = may_create(dir, dentry);
3800         unsigned max_links = dir->i_sb->s_max_links;
3801 
3802         if (error)
3803                 return error;
3804 
3805         if (!dir->i_op->mkdir)
3806                 return -EPERM;
3807 
3808         mode &= (S_IRWXUGO|S_ISVTX);
3809         error = security_inode_mkdir(dir, dentry, mode);
3810         if (error)
3811                 return error;
3812 
3813         if (max_links && dir->i_nlink >= max_links)
3814                 return -EMLINK;
3815 
3816         error = dir->i_op->mkdir(dir, dentry, mode);
3817         if (!error)
3818                 fsnotify_mkdir(dir, dentry);
3819         return error;
3820 }
3821 EXPORT_SYMBOL(vfs_mkdir);
3822 
3823 long do_mkdirat(int dfd, const char __user *pathname, umode_t mode)
3824 {
3825         struct dentry *dentry;
3826         struct path path;
3827         int error;
3828         unsigned int lookup_flags = LOOKUP_DIRECTORY;
3829 
3830 retry:
3831         dentry = user_path_create(dfd, pathname, &path, lookup_flags);
3832         if (IS_ERR(dentry))
3833                 return PTR_ERR(dentry);
3834 
3835         if (!IS_POSIXACL(path.dentry->d_inode))
3836                 mode &= ~current_umask();
3837         error = security_path_mkdir(&path, dentry, mode);
3838         if (!error)
3839                 error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
3840         done_path_create(&path, dentry);
3841         if (retry_estale(error, lookup_flags)) {
3842                 lookup_flags |= LOOKUP_REVAL;
3843                 goto retry;
3844         }
3845         return error;
3846 }
3847 
3848 SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
3849 {
3850         return do_mkdirat(dfd, pathname, mode);
3851 }
3852 
3853 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
3854 {
3855         return do_mkdirat(AT_FDCWD, pathname, mode);
3856 }
3857 
3858 int vfs_rmdir(struct inode *dir, struct dentry *dentry)
3859 {
3860         int error = may_delete(dir, dentry, 1);
3861 
3862         if (error)
3863                 return error;
3864 
3865         if (!dir->i_op->rmdir)
3866                 return -EPERM;
3867 
3868         dget(dentry);
3869         inode_lock(dentry->d_inode);
3870 
3871         error = -EBUSY;
3872         if (is_local_mountpoint(dentry))
3873                 goto out;
3874 
3875         error = security_inode_rmdir(dir, dentry);
3876         if (error)
3877                 goto out;
3878 
3879         error = dir->i_op->rmdir(dir, dentry);
3880         if (error)
3881                 goto out;
3882 
3883         shrink_dcache_parent(dentry);
3884         dentry->d_inode->i_flags |= S_DEAD;
3885         dont_mount(dentry);
3886         detach_mounts(dentry);
3887 
3888 out:
3889         inode_unlock(dentry->d_inode);
3890         dput(dentry);
3891         if (!error)
3892                 d_delete(dentry);
3893         return error;
3894 }
3895 EXPORT_SYMBOL(vfs_rmdir);
3896 
3897 long do_rmdir(int dfd, const char __user *pathname)
3898 {
3899         int error = 0;
3900         struct filename *name;
3901         struct dentry *dentry;
3902         struct path path;
3903         struct qstr last;
3904         int type;
3905         unsigned int lookup_flags = 0;
3906 retry:
3907         name = filename_parentat(dfd, getname(pathname), lookup_flags,
3908                                 &path, &last, &type);
3909         if (IS_ERR(name))
3910                 return PTR_ERR(name);
3911 
3912         switch (type) {
3913         case LAST_DOTDOT:
3914                 error = -ENOTEMPTY;
3915                 goto exit1;
3916         case LAST_DOT:
3917                 error = -EINVAL;
3918                 goto exit1;
3919         case LAST_ROOT:
3920                 error = -EBUSY;
3921                 goto exit1;
3922         }
3923 
3924         error = mnt_want_write(path.mnt);
3925         if (error)
3926                 goto exit1;
3927 
3928         inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
3929         dentry = __lookup_hash(&last, path.dentry, lookup_flags);
3930         error = PTR_ERR(dentry);
3931         if (IS_ERR(dentry))
3932                 goto exit2;
3933         if (!dentry->d_inode) {
3934                 error = -ENOENT;
3935                 goto exit3;
3936         }
3937         error = security_path_rmdir(&path, dentry);
3938         if (error)
3939                 goto exit3;
3940         error = vfs_rmdir(path.dentry->d_inode, dentry);
3941 exit3:
3942         dput(dentry);
3943 exit2:
3944         inode_unlock(path.dentry->d_inode);
3945         mnt_drop_write(path.mnt);
3946 exit1:
3947         path_put(&path);
3948         putname(name);
3949         if (retry_estale(error, lookup_flags)) {
3950                 lookup_flags |= LOOKUP_REVAL;
3951                 goto retry;
3952         }
3953         return error;
3954 }
3955 
3956 SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
3957 {
3958         return do_rmdir(AT_FDCWD, pathname);
3959 }
3960 
3961 /**
3962  * vfs_unlink - unlink a filesystem object
3963  * @dir:        parent directory
3964  * @dentry:     victim
3965  * @delegated_inode: returns victim inode, if the inode is delegated.
3966  *
3967  * The caller must hold dir->i_mutex.
3968  *
3969  * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and
3970  * return a reference to the inode in delegated_inode.  The caller
3971  * should then break the delegation on that inode and retry.  Because
3972  * breaking a delegation may take a long time, the caller should drop
3973  * dir->i_mutex before doing so.
3974  *
3975  * Alternatively, a caller may pass NULL for delegated_inode.  This may
3976  * be appropriate for callers that expect the underlying filesystem not
3977  * to be NFS exported.
3978  */
3979 int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
3980 {
3981         struct inode *target = dentry->d_inode;
3982         int error = may_delete(dir, dentry, 0);
3983 
3984         if (error)
3985                 return error;
3986 
3987         if (!dir->i_op->unlink)
3988                 return -EPERM;
3989 
3990         inode_lock(target);
3991         if (is_local_mountpoint(dentry))
3992                 error = -EBUSY;
3993         else {
3994                 error = security_inode_unlink(dir, dentry);
3995                 if (!error) {
3996                         error = try_break_deleg(target, delegated_inode);
3997                         if (error)
3998                                 goto out;
3999                         error = dir->i_op->unlink(dir, dentry);
4000                         if (!error) {
4001                                 dont_mount(dentry);
4002                                 detach_mounts(dentry);
4003                         }
4004                 }
4005         }
4006 out:
4007         inode_unlock(target);
4008 
4009         /* We don't d_delete() NFS sillyrenamed files--they still exist. */
4010         if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
4011                 fsnotify_link_count(target);
4012                 d_delete(dentry);
4013         }
4014 
4015         return error;
4016 }
4017 EXPORT_SYMBOL(vfs_unlink);
4018 
4019 /*
4020  * Make sure that the actual truncation of the file will occur outside its
4021  * directory's i_mutex.  Truncate can take a long time if there is a lot of
4022  * writeout happening, and we don't want to prevent access to the directory
4023  * while waiting on the I/O.
4024  */
4025 long do_unlinkat(int dfd, struct filename *name)
4026 {
4027         int error;
4028         struct dentry *dentry;
4029         struct path path;
4030         struct qstr last;
4031         int type;
4032         struct inode *inode = NULL;
4033         struct inode *delegated_inode = NULL;
4034         unsigned int lookup_flags = 0;
4035 retry:
4036         name = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
4037         if (IS_ERR(name))
4038                 return PTR_ERR(name);
4039 
4040         error = -EISDIR;
4041         if (type != LAST_NORM)
4042                 goto exit1;
4043 
4044         error = mnt_want_write(path.mnt);
4045         if (error)
4046                 goto exit1;
4047 retry_deleg:
4048         inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
4049         dentry = __lookup_hash(&last, path.dentry, lookup_flags);
4050         error = PTR_ERR(dentry);
4051         if (!IS_ERR(dentry)) {
4052                 /* Why not before? Because we want correct error value */
4053                 if (last.name[last.len])
4054                         goto slashes;
4055                 inode = dentry->d_inode;
4056                 if (d_is_negative(dentry))
4057                         goto slashes;
4058                 ihold(inode);
4059                 error = security_path_unlink(&path, dentry);
4060                 if (error)
4061                         goto exit2;
4062                 error = vfs_unlink(path.dentry->d_inode, dentry, &delegated_inode);
4063 exit2:
4064                 dput(dentry);
4065         }
4066         inode_unlock(path.dentry->d_inode);
4067         if (inode)
4068                 iput(inode);    /* truncate the inode here */
4069         inode = NULL;
4070         if (delegated_inode) {
4071                 error = break_deleg_wait(&delegated_inode);
4072                 if (!error)
4073                         goto retry_deleg;
4074         }
4075         mnt_drop_write(path.mnt);
4076 exit1:
4077         path_put(&path);
4078         if (retry_estale(error, lookup_flags)) {
4079                 lookup_flags |= LOOKUP_REVAL;
4080                 inode = NULL;
4081                 goto retry;
4082         }
4083         putname(name);
4084         return error;
4085 
4086 slashes:
4087         if (d_is_negative(dentry))
4088                 error = -ENOENT;
4089         else if (d_is_dir(dentry))
4090                 error = -EISDIR;
4091         else
4092                 error = -ENOTDIR;
4093         goto exit2;
4094 }
4095 
4096 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
4097 {
4098         if ((flag & ~AT_REMOVEDIR) != 0)
4099                 return -EINVAL;
4100 
4101         if (flag & AT_REMOVEDIR)
4102                 return do_rmdir(dfd, pathname);
4103 
4104         return do_unlinkat(dfd, getname(pathname));
4105 }
4106 
4107 SYSCALL_DEFINE1(unlink, const char __user *, pathname)
4108 {
4109         return do_unlinkat(AT_FDCWD, getname(pathname));
4110 }
4111 
4112 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
4113 {
4114         int error = may_create(dir, dentry);
4115 
4116         if (error)
4117                 return error;
4118 
4119         if (!dir->i_op->symlink)
4120                 return -EPERM;
4121 
4122         error = security_inode_symlink(dir, dentry, oldname);
4123         if (error)
4124                 return error;
4125 
4126         error = dir->i_op->symlink(dir, dentry, oldname);
4127         if (!error)
4128                 fsnotify_create(dir, dentry);
4129         return error;
4130 }
4131 EXPORT_SYMBOL(vfs_symlink);
4132 
4133 long do_symlinkat(const char __user *oldname, int newdfd,
4134                   const char __user *newname)
4135 {
4136         int error;
4137         struct filename *from;
4138         struct dentry *dentry;
4139         struct path path;
4140         unsigned int lookup_flags = 0;
4141 
4142         from = getname(oldname);
4143         if (IS_ERR(from))
4144                 return PTR_ERR(from);
4145 retry:
4146         dentry = user_path_create(newdfd, newname, &path, lookup_flags);
4147         error = PTR_ERR(dentry);
4148         if (IS_ERR(dentry))
4149                 goto out_putname;
4150 
4151         error = security_path_symlink(&path, dentry, from->name);
4152         if (!error)
4153                 error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
4154         done_path_create(&path, dentry);
4155         if (retry_estale(error, lookup_flags)) {
4156                 lookup_flags |= LOOKUP_REVAL;
4157                 goto retry;
4158         }
4159 out_putname:
4160         putname(from);
4161         return error;
4162 }
4163 
4164 SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
4165                 int, newdfd, const char __user *, newname)
4166 {
4167         return do_symlinkat(oldname, newdfd, newname);
4168 }
4169 
4170 SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
4171 {
4172         return do_symlinkat(oldname, AT_FDCWD, newname);
4173 }
4174 
4175 /**
4176  * vfs_link - create a new link
4177  * @old_dentry: object to be linked
4178  * @dir:        new parent
4179  * @new_dentry: where to create the new link
4180  * @delegated_inode: returns inode needing a delegation break
4181  *
4182  * The caller must hold dir->i_mutex
4183  *
4184  * If vfs_link discovers a delegation on the to-be-linked file in need
4185  * of breaking, it will return -EWOULDBLOCK and return a reference to the
4186  * inode in delegated_inode.  The caller should then break the delegation
4187  * and retry.  Because breaking a delegation may take a long time, the
4188  * caller should drop the i_mutex before doing so.
4189  *
4190  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4191  * be appropriate for callers that expect the underlying filesystem not
4192  * to be NFS exported.
4193  */
4194 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
4195 {
4196         struct inode *inode = old_dentry->d_inode;
4197         unsigned max_links = dir->i_sb->s_max_links;
4198         int error;
4199 
4200         if (!inode)
4201                 return -ENOENT;
4202 
4203         error = may_create(dir, new_dentry);
4204         if (error)
4205                 return error;
4206 
4207         if (dir->i_sb != inode->i_sb)
4208                 return -EXDEV;
4209 
4210         /*
4211          * A link to an append-only or immutable file cannot be created.
4212          */
4213         if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
4214                 return -EPERM;
4215         /*
4216          * Updating the link count will likely cause i_uid and i_gid to
4217          * be writen back improperly if their true value is unknown to
4218          * the vfs.
4219          */
4220         if (HAS_UNMAPPED_ID(inode))
4221                 return -EPERM;
4222         if (!dir->i_op->link)
4223                 return -EPERM;
4224         if (S_ISDIR(inode->i_mode))
4225                 return -EPERM;
4226 
4227         error = security_inode_link(old_dentry, dir, new_dentry);
4228         if (error)
4229                 return error;
4230 
4231         inode_lock(inode);
4232         /* Make sure we don't allow creating hardlink to an unlinked file */
4233         if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
4234                 error =  -ENOENT;
4235         else if (max_links && inode->i_nlink >= max_links)
4236                 error = -EMLINK;
4237         else {
4238                 error = try_break_deleg(inode, delegated_inode);
4239                 if (!error)
4240                         error = dir->i_op->link(old_dentry, dir, new_dentry);
4241         }
4242 
4243         if (!error && (inode->i_state & I_LINKABLE)) {
4244                 spin_lock(&inode->i_lock);
4245                 inode->i_state &= ~I_LINKABLE;
4246                 spin_unlock(&inode->i_lock);
4247         }
4248         inode_unlock(inode);
4249         if (!error)
4250                 fsnotify_link(dir, inode, new_dentry);
4251         return error;
4252 }
4253 EXPORT_SYMBOL(vfs_link);
4254 
4255 /*
4256  * Hardlinks are often used in delicate situations.  We avoid
4257  * security-related surprises by not following symlinks on the
4258  * newname.  --KAB
4259  *
4260  * We don't follow them on the oldname either to be compatible
4261  * with linux 2.0, and to avoid hard-linking to directories
4262  * and other special files.  --ADM
4263  */
4264 int do_linkat(int olddfd, const char __user *oldname, int newdfd,
4265               const char __user *newname, int flags)
4266 {
4267         struct dentry *new_dentry;
4268         struct path old_path, new_path;
4269         struct inode *delegated_inode = NULL;
4270         int how = 0;
4271         int error;
4272 
4273         if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
4274                 return -EINVAL;
4275         /*
4276          * To use null names we require CAP_DAC_READ_SEARCH
4277          * This ensures that not everyone will be able to create
4278          * handlink using the passed filedescriptor.
4279          */
4280         if (flags & AT_EMPTY_PATH) {
4281                 if (!capable(CAP_DAC_READ_SEARCH))
4282                         return -ENOENT;
4283                 how = LOOKUP_EMPTY;
4284         }
4285 
4286         if (flags & AT_SYMLINK_FOLLOW)
4287                 how |= LOOKUP_FOLLOW;
4288 retry:
4289         error = user_path_at(olddfd, oldname, how, &old_path);
4290         if (error)
4291                 return error;
4292 
4293         new_dentry = user_path_create(newdfd, newname, &new_path,
4294                                         (how & LOOKUP_REVAL));
4295         error = PTR_ERR(new_dentry);
4296         if (IS_ERR(new_dentry))
4297                 goto out;
4298 
4299         error = -EXDEV;
4300         if (old_path.mnt != new_path.mnt)
4301                 goto out_dput;
4302         error = may_linkat(&old_path);
4303         if (unlikely(error))
4304                 goto out_dput;
4305         error = security_path_link(old_path.dentry, &new_path, new_dentry);
4306         if (error)
4307                 goto out_dput;
4308         error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode);
4309 out_dput:
4310         done_path_create(&new_path, new_dentry);
4311         if (delegated_inode) {
4312                 error = break_deleg_wait(&delegated_inode);
4313                 if (!error) {
4314                         path_put(&old_path);
4315                         goto retry;
4316                 }
4317         }
4318         if (retry_estale(error, how)) {
4319                 path_put(&old_path);
4320                 how |= LOOKUP_REVAL;
4321                 goto retry;
4322         }
4323 out:
4324         path_put(&old_path);
4325 
4326         return error;
4327 }
4328 
4329 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
4330                 int, newdfd, const char __user *, newname, int, flags)
4331 {
4332         return do_linkat(olddfd, oldname, newdfd, newname, flags);
4333 }
4334 
4335 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
4336 {
4337         return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4338 }
4339 
4340 /**
4341  * vfs_rename - rename a filesystem object
4342  * @old_dir:    parent of source
4343  * @old_dentry: source
4344  * @new_dir:    parent of destination
4345  * @new_dentry: destination
4346  * @delegated_inode: returns an inode needing a delegation break
4347  * @flags:      rename flags
4348  *
4349  * The caller must hold multiple mutexes--see lock_rename()).
4350  *
4351  * If vfs_rename discovers a delegation in need of breaking at either
4352  * the source or destination, it will return -EWOULDBLOCK and return a
4353  * reference to the inode in delegated_inode.  The caller should then
4354  * break the delegation and retry.  Because breaking a delegation may
4355  * take a long time, the caller should drop all locks before doing
4356  * so.
4357  *
4358  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4359  * be appropriate for callers that expect the underlying filesystem not
4360  * to be NFS exported.
4361  *
4362  * The worst of all namespace operations - renaming directory. "Perverted"
4363  * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
4364  * Problems:
4365  *
4366  *      a) we can get into loop creation.
4367  *      b) race potential - two innocent renames can create a loop together.
4368  *         That's where 4.4 screws up. Current fix: serialization on
4369  *         sb->s_vfs_rename_mutex. We might be more accurate, but that's another
4370  *         story.
4371  *      c) we have to lock _four_ objects - parents and victim (if it exists),
4372  *         and source (if it is not a directory).
4373  *         And that - after we got ->i_mutex on parents (until then we don't know
4374  *         whether the target exists).  Solution: try to be smart with locking
4375  *         order for inodes.  We rely on the fact that tree topology may change
4376  *         only under ->s_vfs_rename_mutex _and_ that parent of the object we
4377  *         move will be locked.  Thus we can rank directories by the tree
4378  *         (ancestors first) and rank all non-directories after them.
4379  *         That works since everybody except rename does "lock parent, lookup,
4380  *         lock child" and rename is under ->s_vfs_rename_mutex.
4381  *         HOWEVER, it relies on the assumption that any object with ->lookup()
4382  *         has no more than 1 dentry.  If "hybrid" objects will ever appear,
4383  *         we'd better make sure that there's no link(2) for them.
4384  *      d) conversion from fhandle to dentry may come in the wrong moment - when
4385  *         we are removing the target. Solution: we will have to grab ->i_mutex
4386  *         in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
4387  *         ->i_mutex on parents, which works but leads to some truly excessive
4388  *         locking].
4389  */
4390 int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
4391                struct inode *new_dir, struct dentry *new_dentry,
4392                struct inode **delegated_inode, unsigned int flags)
4393 {
4394         int error;
4395         bool is_dir = d_is_dir(old_dentry);
4396         struct inode *source = old_dentry->d_inode;
4397         struct inode *target = new_dentry->d_inode;
4398         bool new_is_dir = false;
4399         unsigned max_links = new_dir->i_sb->s_max_links;
4400         struct name_snapshot old_name;
4401 
4402         if (source == target)
4403                 return 0;
4404 
4405         error = may_delete(old_dir, old_dentry, is_dir);
4406         if (error)
4407                 return error;
4408 
4409         if (!target) {
4410                 error = may_create(new_dir, new_dentry);
4411         } else {
4412                 new_is_dir = d_is_dir(new_dentry);
4413 
4414                 if (!(flags & RENAME_EXCHANGE))
4415                         error = may_delete(new_dir, new_dentry, is_dir);
4416                 else
4417                         error = may_delete(new_dir, new_dentry, new_is_dir);
4418         }
4419         if (error)
4420                 return error;
4421 
4422         if (!old_dir->i_op->rename)
4423                 return -EPERM;
4424 
4425         /*
4426          * If we are going to change the parent - check write permissions,
4427          * we'll need to flip '..'.
4428          */
4429         if (new_dir != old_dir) {
4430                 if (is_dir) {
4431                         error = inode_permission(source, MAY_WRITE);
4432                         if (error)
4433                                 return error;
4434                 }
4435                 if ((flags & RENAME_EXCHANGE) && new_is_dir) {
4436                         error = inode_permission(target, MAY_WRITE);
4437                         if (error)
4438                                 return error;
4439                 }
4440         }
4441 
4442         error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
4443                                       flags);
4444         if (error)
4445                 return error;
4446 
4447         take_dentry_name_snapshot(&old_name, old_dentry);
4448         dget(new_dentry);
4449         if (!is_dir || (flags & RENAME_EXCHANGE))
4450                 lock_two_nondirectories(source, target);
4451         else if (target)
4452                 inode_lock(target);
4453 
4454         error = -EBUSY;
4455         if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
4456                 goto out;
4457 
4458         if (max_links && new_dir != old_dir) {
4459                 error = -EMLINK;
4460                 if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
4461                         goto out;
4462                 if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
4463                     old_dir->i_nlink >= max_links)
4464                         goto out;
4465         }
4466         if (!is_dir) {
4467                 error = try_break_deleg(source, delegated_inode);
4468                 if (error)
4469                         goto out;
4470         }
4471         if (target && !new_is_dir) {
4472                 error = try_break_deleg(target, delegated_inode);
4473                 if (error)
4474                         goto out;
4475         }
4476         error = old_dir->i_op->rename(old_dir, old_dentry,
4477                                        new_dir, new_dentry, flags);
4478         if (error)
4479                 goto out;
4480 
4481         if (!(flags & RENAME_EXCHANGE) && target) {
4482                 if (is_dir) {
4483                         shrink_dcache_parent(new_dentry);
4484                         target->i_flags |= S_DEAD;
4485                 }
4486                 dont_mount(new_dentry);
4487                 detach_mounts(new_dentry);
4488         }
4489         if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
4490                 if (!(flags & RENAME_EXCHANGE))
4491                         d_move(old_dentry, new_dentry);
4492                 else
4493                         d_exchange(old_dentry, new_dentry);
4494         }
4495 out:
4496         if (!is_dir || (flags & RENAME_EXCHANGE))
4497                 unlock_two_nondirectories(source, target);
4498         else if (target)
4499                 inode_unlock(target);
4500         dput(new_dentry);
4501         if (!error) {
4502                 fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
4503                               !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
4504                 if (flags & RENAME_EXCHANGE) {
4505                         fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
4506                                       new_is_dir, NULL, new_dentry);
4507                 }
4508         }
4509         release_dentry_name_snapshot(&old_name);
4510 
4511         return error;
4512 }
4513 EXPORT_SYMBOL(vfs_rename);
4514 
4515 static int do_renameat2(int olddfd, const char __user *oldname, int newdfd,
4516                         const char __user *newname, unsigned int flags)
4517 {
4518         struct dentry *old_dentry, *new_dentry;
4519         struct dentry *trap;
4520         struct path old_path, new_path;
4521         struct qstr old_last, new_last;
4522         int old_type, new_type;
4523         struct inode *delegated_inode = NULL;
4524         struct filename *from;
4525         struct filename *to;
4526         unsigned int lookup_flags = 0, target_flags = LOOKUP_RENAME_TARGET;
4527         bool should_retry = false;
4528         int error;
4529 
4530         if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
4531                 return -EINVAL;
4532 
4533         if ((flags & (RENAME_NOREPLACE | RENAME_WHITEOUT)) &&
4534             (flags & RENAME_EXCHANGE))
4535                 return -EINVAL;
4536 
4537         if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD))
4538                 return -EPERM;
4539 
4540         if (flags & RENAME_EXCHANGE)
4541                 target_flags = 0;
4542 
4543 retry:
4544         from = filename_parentat(olddfd, getname(oldname), lookup_flags,
4545                                 &old_path, &old_last, &old_type);
4546         if (IS_ERR(from)) {
4547                 error = PTR_ERR(from);
4548                 goto exit;
4549         }
4550 
4551         to = filename_parentat(newdfd, getname(newname), lookup_flags,
4552                                 &new_path, &new_last, &new_type);
4553         if (IS_ERR(to)) {
4554                 error = PTR_ERR(to);
4555                 goto exit1;
4556         }
4557 
4558         error = -EXDEV;
4559         if (old_path.mnt != new_path.mnt)
4560                 goto exit2;
4561 
4562         error = -EBUSY;
4563         if (old_type != LAST_NORM)
4564                 goto exit2;
4565 
4566         if (flags & RENAME_NOREPLACE)
4567                 error = -EEXIST;
4568         if (new_type != LAST_NORM)
4569                 goto exit2;
4570 
4571         error = mnt_want_write(old_path.mnt);
4572         if (error)
4573                 goto exit2;
4574 
4575 retry_deleg:
4576         trap = lock_rename(new_path.dentry, old_path.dentry);
4577 
4578         old_dentry = __lookup_hash(&old_last, old_path.dentry, lookup_flags);
4579         error = PTR_ERR(old_dentry);
4580         if (IS_ERR(old_dentry))
4581                 goto exit3;
4582         /* source must exist */
4583         error = -ENOENT;
4584         if (d_is_negative(old_dentry))
4585                 goto exit4;
4586         new_dentry = __lookup_hash(&new_last, new_path.dentry, lookup_flags | target_flags);
4587         error = PTR_ERR(new_dentry);
4588         if (IS_ERR(new_dentry))
4589                 goto exit4;
4590         error = -EEXIST;
4591         if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
4592                 goto exit5;
4593         if (flags & RENAME_EXCHANGE) {
4594                 error = -ENOENT;
4595                 if (d_is_negative(new_dentry))
4596                         goto exit5;
4597 
4598                 if (!d_is_dir(new_dentry)) {
4599                         error = -ENOTDIR;
4600                         if (new_last.name[new_last.len])
4601                                 goto exit5;
4602                 }
4603         }
4604         /* unless the source is a directory trailing slashes give -ENOTDIR */
4605         if (!d_is_dir(old_dentry)) {
4606                 error = -ENOTDIR;
4607                 if (old_last.name[old_last.len])
4608                         goto exit5;
4609                 if (!(flags & RENAME_EXCHANGE) && new_last.name[new_last.len])
4610                         goto exit5;
4611         }
4612         /* source should not be ancestor of target */
4613         error = -EINVAL;
4614         if (old_dentry == trap)
4615                 goto exit5;
4616         /* target should not be an ancestor of source */
4617         if (!(flags & RENAME_EXCHANGE))
4618                 error = -ENOTEMPTY;
4619         if (new_dentry == trap)
4620                 goto exit5;
4621 
4622         error = security_path_rename(&old_path, old_dentry,
4623                                      &new_path, new_dentry, flags);
4624         if (error)
4625                 goto exit5;
4626         error = vfs_rename(old_path.dentry->d_inode, old_dentry,
4627                            new_path.dentry->d_inode, new_dentry,
4628                            &delegated_inode, flags);
4629 exit5:
4630         dput(new_dentry);
4631 exit4:
4632         dput(old_dentry);
4633 exit3:
4634         unlock_rename(new_path.dentry, old_path.dentry);
4635         if (delegated_inode) {
4636                 error = break_deleg_wait(&delegated_inode);
4637                 if (!error)
4638                         goto retry_deleg;
4639         }
4640         mnt_drop_write(old_path.mnt);
4641 exit2:
4642         if (retry_estale(error, lookup_flags))
4643                 should_retry = true;
4644         path_put(&new_path);
4645         putname(to);
4646 exit1:
4647         path_put(&old_path);
4648         putname(from);
4649         if (should_retry) {
4650                 should_retry = false;
4651                 lookup_flags |= LOOKUP_REVAL;
4652                 goto retry;
4653         }
4654 exit:
4655         return error;
4656 }
4657 
4658 SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
4659                 int, newdfd, const char __user *, newname, unsigned int, flags)
4660 {
4661         return do_renameat2(olddfd, oldname, newdfd, newname, flags);
4662 }
4663 
4664 SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
4665                 int, newdfd, const char __user *, newname)
4666 {
4667         return do_renameat2(olddfd, oldname, newdfd, newname, 0);
4668 }
4669 
4670 SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
4671 {
4672         return do_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4673 }
4674 
4675 int vfs_whiteout(struct inode *dir, struct dentry *dentry)
4676 {
4677         int error = may_create(dir, dentry);
4678         if (error)
4679                 return error;
4680 
4681         if (!dir->i_op->mknod)
4682                 return -EPERM;
4683 
4684         return dir->i_op->mknod(dir, dentry,
4685                                 S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
4686 }
4687 EXPORT_SYMBOL(vfs_whiteout);
4688 
4689 int readlink_copy(char __user *buffer, int buflen, const char *link)
4690 {
4691         int len = PTR_ERR(link);
4692         if (IS_ERR(link))
4693                 goto out;
4694 
4695         len = strlen(link);
4696         if (len > (unsigned) buflen)
4697                 len = buflen;
4698         if (copy_to_user(buffer, link, len))
4699                 len = -EFAULT;
4700 out:
4701         return len;
4702 }
4703 
4704 /**
4705  * vfs_readlink - copy symlink body into userspace buffer
4706  * @dentry: dentry on which to get symbolic link
4707  * @buffer: user memory pointer
4708  * @buflen: size of buffer
4709  *
4710  * Does not touch atime.  That's up to the caller if necessary
4711  *
4712  * Does not call security hook.
4713  */
4714 int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4715 {
4716         struct inode *inode = d_inode(dentry);
4717         DEFINE_DELAYED_CALL(done);
4718         const char *link;
4719         int res;
4720 
4721         if (unlikely(!(inode->i_opflags & IOP_DEFAULT_READLINK))) {
4722                 if (unlikely(inode->i_op->readlink))
4723                         return inode->i_op->readlink(dentry, buffer, buflen);
4724 
4725                 if (!d_is_symlink(dentry))
4726                         return -EINVAL;
4727 
4728                 spin_lock(&inode->i_lock);
4729                 inode->i_opflags |= IOP_DEFAULT_READLINK;
4730                 spin_unlock(&inode->i_lock);
4731         }
4732 
4733         link = inode->i_link;
4734         if (!link) {
4735                 link = inode->i_op->get_link(dentry, inode, &done);
4736                 if (IS_ERR(link))
4737                         return PTR_ERR(link);
4738         }
4739         res = readlink_copy(buffer, buflen, link);
4740         do_delayed_call(&done);
4741         return res;
4742 }
4743 EXPORT_SYMBOL(vfs_readlink);
4744 
4745 /**
4746  * vfs_get_link - get symlink body
4747  * @dentry: dentry on which to get symbolic link
4748  * @done: caller needs to free returned data with this
4749  *
4750  * Calls security hook and i_op->get_link() on the supplied inode.
4751  *
4752  * It does not touch atime.  That's up to the caller if necessary.
4753  *
4754  * Does not work on "special" symlinks like /proc/$$/fd/N
4755  */
4756 const char *vfs_get_link(struct dentry *dentry, struct delayed_call *done)
4757 {
4758         const char *res = ERR_PTR(-EINVAL);
4759         struct inode *inode = d_inode(dentry);
4760 
4761         if (d_is_symlink(dentry)) {
4762                 res = ERR_PTR(security_inode_readlink(dentry));
4763                 if (!res)
4764                         res = inode->i_op->get_link(dentry, inode, done);
4765         }
4766         return res;
4767 }
4768 EXPORT_SYMBOL(vfs_get_link);
4769 
4770 /* get the link contents into pagecache */
4771 const char *page_get_link(struct dentry *dentry, struct inode *inode,
4772                           struct delayed_call *callback)
4773 {
4774         char *kaddr;
4775         struct page *page;
4776         struct address_space *mapping = inode->i_mapping;
4777 
4778         if (!dentry) {
4779                 page = find_get_page(mapping, 0);
4780                 if (!page)
4781                         return ERR_PTR(-ECHILD);
4782                 if (!PageUptodate(page)) {
4783                         put_page(page);
4784                         return ERR_PTR(-ECHILD);
4785                 }
4786         } else {
4787                 page = read_mapping_page(mapping, 0, NULL);
4788                 if (IS_ERR(page))
4789                         return (char*)page;
4790         }
4791         set_delayed_call(callback, page_put_link, page);
4792         BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
4793         kaddr = page_address(page);
4794         nd_terminate_link(kaddr, inode->i_size, PAGE_SIZE - 1);
4795         return kaddr;
4796 }
4797 
4798 EXPORT_SYMBOL(page_get_link);
4799 
4800 void page_put_link(void *arg)
4801 {
4802         put_page(arg);
4803 }
4804 EXPORT_SYMBOL(page_put_link);
4805 
4806 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4807 {
4808         DEFINE_DELAYED_CALL(done);
4809         int res = readlink_copy(buffer, buflen,
4810                                 page_get_link(dentry, d_inode(dentry),
4811                                               &done));
4812         do_delayed_call(&done);
4813         return res;
4814 }
4815 EXPORT_SYMBOL(page_readlink);
4816 
4817 /*
4818  * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
4819  */
4820 int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
4821 {
4822         struct address_space *mapping = inode->i_mapping;
4823         struct page *page;
4824         void *fsdata;
4825         int err;
4826         unsigned int flags = 0;
4827         if (nofs)
4828                 flags |= AOP_FLAG_NOFS;
4829 
4830 retry:
4831         err = pagecache_write_begin(NULL, mapping, 0, len-1,
4832                                 flags, &page, &fsdata);
4833         if (err)
4834                 goto fail;
4835 
4836         memcpy(page_address(page), symname, len-1);
4837 
4838         err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
4839                                                         page, fsdata);
4840         if (err < 0)
4841                 goto fail;
4842         if (err < len-1)
4843                 goto retry;
4844 
4845         mark_inode_dirty(inode);
4846         return 0;
4847 fail:
4848         return err;
4849 }
4850 EXPORT_SYMBOL(__page_symlink);
4851 
4852 int page_symlink(struct inode *inode, const char *symname, int len)
4853 {
4854         return __page_symlink(inode, symname, len,
4855                         !mapping_gfp_constraint(inode->i_mapping, __GFP_FS));
4856 }
4857 EXPORT_SYMBOL(page_symlink);
4858 
4859 const struct inode_operations page_symlink_inode_operations = {
4860         .get_link       = page_get_link,
4861 };
4862 EXPORT_SYMBOL(page_symlink_inode_operations);
4863 

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