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

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