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TOMOYO Linux Cross Reference
Linux/fs/overlayfs/inode.c

Version: ~ [ linux-5.5-rc6 ] ~ [ linux-5.4.11 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.95 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.164 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.209 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.209 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.81 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
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  1 /*
  2  *
  3  * Copyright (C) 2011 Novell Inc.
  4  *
  5  * This program is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 as published by
  7  * the Free Software Foundation.
  8  */
  9 
 10 #include <linux/fs.h>
 11 #include <linux/slab.h>
 12 #include <linux/cred.h>
 13 #include <linux/xattr.h>
 14 #include <linux/posix_acl.h>
 15 #include <linux/ratelimit.h>
 16 #include "overlayfs.h"
 17 
 18 
 19 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 20 {
 21         int err;
 22         bool full_copy_up = false;
 23         struct dentry *upperdentry;
 24         const struct cred *old_cred;
 25 
 26         err = setattr_prepare(dentry, attr);
 27         if (err)
 28                 return err;
 29 
 30         err = ovl_want_write(dentry);
 31         if (err)
 32                 goto out;
 33 
 34         if (attr->ia_valid & ATTR_SIZE) {
 35                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
 36 
 37                 err = -ETXTBSY;
 38                 if (atomic_read(&realinode->i_writecount) < 0)
 39                         goto out_drop_write;
 40 
 41                 /* Truncate should trigger data copy up as well */
 42                 full_copy_up = true;
 43         }
 44 
 45         if (!full_copy_up)
 46                 err = ovl_copy_up(dentry);
 47         else
 48                 err = ovl_copy_up_with_data(dentry);
 49         if (!err) {
 50                 struct inode *winode = NULL;
 51 
 52                 upperdentry = ovl_dentry_upper(dentry);
 53 
 54                 if (attr->ia_valid & ATTR_SIZE) {
 55                         winode = d_inode(upperdentry);
 56                         err = get_write_access(winode);
 57                         if (err)
 58                                 goto out_drop_write;
 59                 }
 60 
 61                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
 62                         attr->ia_valid &= ~ATTR_MODE;
 63 
 64                 inode_lock(upperdentry->d_inode);
 65                 old_cred = ovl_override_creds(dentry->d_sb);
 66                 err = notify_change(upperdentry, attr, NULL);
 67                 revert_creds(old_cred);
 68                 if (!err)
 69                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
 70                 inode_unlock(upperdentry->d_inode);
 71 
 72                 if (winode)
 73                         put_write_access(winode);
 74         }
 75 out_drop_write:
 76         ovl_drop_write(dentry);
 77 out:
 78         return err;
 79 }
 80 
 81 static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat,
 82                            struct ovl_layer *lower_layer)
 83 {
 84         bool samefs = ovl_same_sb(dentry->d_sb);
 85         unsigned int xinobits = ovl_xino_bits(dentry->d_sb);
 86 
 87         if (samefs) {
 88                 /*
 89                  * When all layers are on the same fs, all real inode
 90                  * number are unique, so we use the overlay st_dev,
 91                  * which is friendly to du -x.
 92                  */
 93                 stat->dev = dentry->d_sb->s_dev;
 94                 return 0;
 95         } else if (xinobits) {
 96                 unsigned int shift = 64 - xinobits;
 97                 /*
 98                  * All inode numbers of underlying fs should not be using the
 99                  * high xinobits, so we use high xinobits to partition the
100                  * overlay st_ino address space. The high bits holds the fsid
101                  * (upper fsid is 0). This way overlay inode numbers are unique
102                  * and all inodes use overlay st_dev. Inode numbers are also
103                  * persistent for a given layer configuration.
104                  */
105                 if (stat->ino >> shift) {
106                         pr_warn_ratelimited("overlayfs: inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
107                                             dentry, stat->ino, xinobits);
108                 } else {
109                         if (lower_layer)
110                                 stat->ino |= ((u64)lower_layer->fsid) << shift;
111 
112                         stat->dev = dentry->d_sb->s_dev;
113                         return 0;
114                 }
115         }
116 
117         /* The inode could not be mapped to a unified st_ino address space */
118         if (S_ISDIR(dentry->d_inode->i_mode)) {
119                 /*
120                  * Always use the overlay st_dev for directories, so 'find
121                  * -xdev' will scan the entire overlay mount and won't cross the
122                  * overlay mount boundaries.
123                  *
124                  * If not all layers are on the same fs the pair {real st_ino;
125                  * overlay st_dev} is not unique, so use the non persistent
126                  * overlay st_ino for directories.
127                  */
128                 stat->dev = dentry->d_sb->s_dev;
129                 stat->ino = dentry->d_inode->i_ino;
130         } else if (lower_layer && lower_layer->fsid) {
131                 /*
132                  * For non-samefs setup, if we cannot map all layers st_ino
133                  * to a unified address space, we need to make sure that st_dev
134                  * is unique per lower fs. Upper layer uses real st_dev and
135                  * lower layers use the unique anonymous bdev assigned to the
136                  * lower fs.
137                  */
138                 stat->dev = lower_layer->fs->pseudo_dev;
139         }
140 
141         return 0;
142 }
143 
144 int ovl_getattr(const struct path *path, struct kstat *stat,
145                 u32 request_mask, unsigned int flags)
146 {
147         struct dentry *dentry = path->dentry;
148         enum ovl_path_type type;
149         struct path realpath;
150         const struct cred *old_cred;
151         bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
152         bool samefs = ovl_same_sb(dentry->d_sb);
153         struct ovl_layer *lower_layer = NULL;
154         int err;
155         bool metacopy_blocks = false;
156 
157         metacopy_blocks = ovl_is_metacopy_dentry(dentry);
158 
159         type = ovl_path_real(dentry, &realpath);
160         old_cred = ovl_override_creds(dentry->d_sb);
161         err = vfs_getattr(&realpath, stat, request_mask, flags);
162         if (err)
163                 goto out;
164 
165         /*
166          * For non-dir or same fs, we use st_ino of the copy up origin.
167          * This guaranties constant st_dev/st_ino across copy up.
168          * With xino feature and non-samefs, we use st_ino of the copy up
169          * origin masked with high bits that represent the layer id.
170          *
171          * If lower filesystem supports NFS file handles, this also guaranties
172          * persistent st_ino across mount cycle.
173          */
174         if (!is_dir || samefs || ovl_xino_bits(dentry->d_sb)) {
175                 if (!OVL_TYPE_UPPER(type)) {
176                         lower_layer = ovl_layer_lower(dentry);
177                 } else if (OVL_TYPE_ORIGIN(type)) {
178                         struct kstat lowerstat;
179                         u32 lowermask = STATX_INO | STATX_BLOCKS |
180                                         (!is_dir ? STATX_NLINK : 0);
181 
182                         ovl_path_lower(dentry, &realpath);
183                         err = vfs_getattr(&realpath, &lowerstat,
184                                           lowermask, flags);
185                         if (err)
186                                 goto out;
187 
188                         /*
189                          * Lower hardlinks may be broken on copy up to different
190                          * upper files, so we cannot use the lower origin st_ino
191                          * for those different files, even for the same fs case.
192                          *
193                          * Similarly, several redirected dirs can point to the
194                          * same dir on a lower layer. With the "verify_lower"
195                          * feature, we do not use the lower origin st_ino, if
196                          * we haven't verified that this redirect is unique.
197                          *
198                          * With inodes index enabled, it is safe to use st_ino
199                          * of an indexed origin. The index validates that the
200                          * upper hardlink is not broken and that a redirected
201                          * dir is the only redirect to that origin.
202                          */
203                         if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
204                             (!ovl_verify_lower(dentry->d_sb) &&
205                              (is_dir || lowerstat.nlink == 1))) {
206                                 stat->ino = lowerstat.ino;
207                                 lower_layer = ovl_layer_lower(dentry);
208                         }
209 
210                         /*
211                          * If we are querying a metacopy dentry and lower
212                          * dentry is data dentry, then use the blocks we
213                          * queried just now. We don't have to do additional
214                          * vfs_getattr(). If lower itself is metacopy, then
215                          * additional vfs_getattr() is unavoidable.
216                          */
217                         if (metacopy_blocks &&
218                             realpath.dentry == ovl_dentry_lowerdata(dentry)) {
219                                 stat->blocks = lowerstat.blocks;
220                                 metacopy_blocks = false;
221                         }
222                 }
223 
224                 if (metacopy_blocks) {
225                         /*
226                          * If lower is not same as lowerdata or if there was
227                          * no origin on upper, we can end up here.
228                          */
229                         struct kstat lowerdatastat;
230                         u32 lowermask = STATX_BLOCKS;
231 
232                         ovl_path_lowerdata(dentry, &realpath);
233                         err = vfs_getattr(&realpath, &lowerdatastat,
234                                           lowermask, flags);
235                         if (err)
236                                 goto out;
237                         stat->blocks = lowerdatastat.blocks;
238                 }
239         }
240 
241         err = ovl_map_dev_ino(dentry, stat, lower_layer);
242         if (err)
243                 goto out;
244 
245         /*
246          * It's probably not worth it to count subdirs to get the
247          * correct link count.  nlink=1 seems to pacify 'find' and
248          * other utilities.
249          */
250         if (is_dir && OVL_TYPE_MERGE(type))
251                 stat->nlink = 1;
252 
253         /*
254          * Return the overlay inode nlinks for indexed upper inodes.
255          * Overlay inode nlink counts the union of the upper hardlinks
256          * and non-covered lower hardlinks. It does not include the upper
257          * index hardlink.
258          */
259         if (!is_dir && ovl_test_flag(OVL_INDEX, d_inode(dentry)))
260                 stat->nlink = dentry->d_inode->i_nlink;
261 
262 out:
263         revert_creds(old_cred);
264 
265         return err;
266 }
267 
268 int ovl_permission(struct inode *inode, int mask)
269 {
270         struct inode *upperinode = ovl_inode_upper(inode);
271         struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
272         const struct cred *old_cred;
273         int err;
274 
275         /* Careful in RCU walk mode */
276         if (!realinode) {
277                 WARN_ON(!(mask & MAY_NOT_BLOCK));
278                 return -ECHILD;
279         }
280 
281         /*
282          * Check overlay inode with the creds of task and underlying inode
283          * with creds of mounter
284          */
285         err = generic_permission(inode, mask);
286         if (err)
287                 return err;
288 
289         old_cred = ovl_override_creds(inode->i_sb);
290         if (!upperinode &&
291             !special_file(realinode->i_mode) && mask & MAY_WRITE) {
292                 mask &= ~(MAY_WRITE | MAY_APPEND);
293                 /* Make sure mounter can read file for copy up later */
294                 mask |= MAY_READ;
295         }
296         err = inode_permission(realinode, mask);
297         revert_creds(old_cred);
298 
299         return err;
300 }
301 
302 static const char *ovl_get_link(struct dentry *dentry,
303                                 struct inode *inode,
304                                 struct delayed_call *done)
305 {
306         const struct cred *old_cred;
307         const char *p;
308 
309         if (!dentry)
310                 return ERR_PTR(-ECHILD);
311 
312         old_cred = ovl_override_creds(dentry->d_sb);
313         p = vfs_get_link(ovl_dentry_real(dentry), done);
314         revert_creds(old_cred);
315         return p;
316 }
317 
318 bool ovl_is_private_xattr(const char *name)
319 {
320         return strncmp(name, OVL_XATTR_PREFIX,
321                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
322 }
323 
324 int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
325                   const void *value, size_t size, int flags)
326 {
327         int err;
328         struct dentry *upperdentry = ovl_i_dentry_upper(inode);
329         struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
330         const struct cred *old_cred;
331 
332         err = ovl_want_write(dentry);
333         if (err)
334                 goto out;
335 
336         if (!value && !upperdentry) {
337                 err = vfs_getxattr(realdentry, name, NULL, 0);
338                 if (err < 0)
339                         goto out_drop_write;
340         }
341 
342         if (!upperdentry) {
343                 err = ovl_copy_up(dentry);
344                 if (err)
345                         goto out_drop_write;
346 
347                 realdentry = ovl_dentry_upper(dentry);
348         }
349 
350         old_cred = ovl_override_creds(dentry->d_sb);
351         if (value)
352                 err = vfs_setxattr(realdentry, name, value, size, flags);
353         else {
354                 WARN_ON(flags != XATTR_REPLACE);
355                 err = vfs_removexattr(realdentry, name);
356         }
357         revert_creds(old_cred);
358 
359         /* copy c/mtime */
360         ovl_copyattr(d_inode(realdentry), inode);
361 
362 out_drop_write:
363         ovl_drop_write(dentry);
364 out:
365         return err;
366 }
367 
368 int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
369                   void *value, size_t size)
370 {
371         ssize_t res;
372         const struct cred *old_cred;
373         struct dentry *realdentry =
374                 ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);
375 
376         old_cred = ovl_override_creds(dentry->d_sb);
377         res = vfs_getxattr(realdentry, name, value, size);
378         revert_creds(old_cred);
379         return res;
380 }
381 
382 static bool ovl_can_list(const char *s)
383 {
384         /* List all non-trusted xatts */
385         if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
386                 return true;
387 
388         /* Never list trusted.overlay, list other trusted for superuser only */
389         return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
390 }
391 
392 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
393 {
394         struct dentry *realdentry = ovl_dentry_real(dentry);
395         ssize_t res;
396         size_t len;
397         char *s;
398         const struct cred *old_cred;
399 
400         old_cred = ovl_override_creds(dentry->d_sb);
401         res = vfs_listxattr(realdentry, list, size);
402         revert_creds(old_cred);
403         if (res <= 0 || size == 0)
404                 return res;
405 
406         /* filter out private xattrs */
407         for (s = list, len = res; len;) {
408                 size_t slen = strnlen(s, len) + 1;
409 
410                 /* underlying fs providing us with an broken xattr list? */
411                 if (WARN_ON(slen > len))
412                         return -EIO;
413 
414                 len -= slen;
415                 if (!ovl_can_list(s)) {
416                         res -= slen;
417                         memmove(s, s + slen, len);
418                 } else {
419                         s += slen;
420                 }
421         }
422 
423         return res;
424 }
425 
426 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
427 {
428         struct inode *realinode = ovl_inode_real(inode);
429         const struct cred *old_cred;
430         struct posix_acl *acl;
431 
432         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
433                 return NULL;
434 
435         old_cred = ovl_override_creds(inode->i_sb);
436         acl = get_acl(realinode, type);
437         revert_creds(old_cred);
438 
439         return acl;
440 }
441 
442 int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags)
443 {
444         if (flags & S_ATIME) {
445                 struct ovl_fs *ofs = inode->i_sb->s_fs_info;
446                 struct path upperpath = {
447                         .mnt = ofs->upper_mnt,
448                         .dentry = ovl_upperdentry_dereference(OVL_I(inode)),
449                 };
450 
451                 if (upperpath.dentry) {
452                         touch_atime(&upperpath);
453                         inode->i_atime = d_inode(upperpath.dentry)->i_atime;
454                 }
455         }
456         return 0;
457 }
458 
459 static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
460                       u64 start, u64 len)
461 {
462         int err;
463         struct inode *realinode = ovl_inode_real(inode);
464         const struct cred *old_cred;
465 
466         if (!realinode->i_op->fiemap)
467                 return -EOPNOTSUPP;
468 
469         old_cred = ovl_override_creds(inode->i_sb);
470 
471         if (fieinfo->fi_flags & FIEMAP_FLAG_SYNC)
472                 filemap_write_and_wait(realinode->i_mapping);
473 
474         err = realinode->i_op->fiemap(realinode, fieinfo, start, len);
475         revert_creds(old_cred);
476 
477         return err;
478 }
479 
480 static const struct inode_operations ovl_file_inode_operations = {
481         .setattr        = ovl_setattr,
482         .permission     = ovl_permission,
483         .getattr        = ovl_getattr,
484         .listxattr      = ovl_listxattr,
485         .get_acl        = ovl_get_acl,
486         .update_time    = ovl_update_time,
487         .fiemap         = ovl_fiemap,
488 };
489 
490 static const struct inode_operations ovl_symlink_inode_operations = {
491         .setattr        = ovl_setattr,
492         .get_link       = ovl_get_link,
493         .getattr        = ovl_getattr,
494         .listxattr      = ovl_listxattr,
495         .update_time    = ovl_update_time,
496 };
497 
498 static const struct inode_operations ovl_special_inode_operations = {
499         .setattr        = ovl_setattr,
500         .permission     = ovl_permission,
501         .getattr        = ovl_getattr,
502         .listxattr      = ovl_listxattr,
503         .get_acl        = ovl_get_acl,
504         .update_time    = ovl_update_time,
505 };
506 
507 static const struct address_space_operations ovl_aops = {
508         /* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */
509         .direct_IO              = noop_direct_IO,
510 };
511 
512 /*
513  * It is possible to stack overlayfs instance on top of another
514  * overlayfs instance as lower layer. We need to annonate the
515  * stackable i_mutex locks according to stack level of the super
516  * block instance. An overlayfs instance can never be in stack
517  * depth 0 (there is always a real fs below it).  An overlayfs
518  * inode lock will use the lockdep annotaion ovl_i_mutex_key[depth].
519  *
520  * For example, here is a snip from /proc/lockdep_chains after
521  * dir_iterate of nested overlayfs:
522  *
523  * [...] &ovl_i_mutex_dir_key[depth]   (stack_depth=2)
524  * [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1)
525  * [...] &type->i_mutex_dir_key        (stack_depth=0)
526  */
527 #define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH
528 
529 static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
530 {
531 #ifdef CONFIG_LOCKDEP
532         static struct lock_class_key ovl_i_mutex_key[OVL_MAX_NESTING];
533         static struct lock_class_key ovl_i_mutex_dir_key[OVL_MAX_NESTING];
534         static struct lock_class_key ovl_i_lock_key[OVL_MAX_NESTING];
535 
536         int depth = inode->i_sb->s_stack_depth - 1;
537 
538         if (WARN_ON_ONCE(depth < 0 || depth >= OVL_MAX_NESTING))
539                 depth = 0;
540 
541         if (S_ISDIR(inode->i_mode))
542                 lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_dir_key[depth]);
543         else
544                 lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_key[depth]);
545 
546         lockdep_set_class(&OVL_I(inode)->lock, &ovl_i_lock_key[depth]);
547 #endif
548 }
549 
550 static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
551                            unsigned long ino, int fsid)
552 {
553         int xinobits = ovl_xino_bits(inode->i_sb);
554 
555         /*
556          * When NFS export is enabled and d_ino is consistent with st_ino
557          * (samefs or i_ino has enough bits to encode layer), set the same
558          * value used for d_ino to i_ino, because nfsd readdirplus compares
559          * d_ino values to i_ino values of child entries. When called from
560          * ovl_new_inode(), ino arg is 0, so i_ino will be updated to real
561          * upper inode i_ino on ovl_inode_init() or ovl_inode_update().
562          */
563         if (inode->i_sb->s_export_op &&
564             (ovl_same_sb(inode->i_sb) || xinobits)) {
565                 inode->i_ino = ino;
566                 if (xinobits && fsid && !(ino >> (64 - xinobits)))
567                         inode->i_ino |= (unsigned long)fsid << (64 - xinobits);
568         } else {
569                 inode->i_ino = get_next_ino();
570         }
571         inode->i_mode = mode;
572         inode->i_flags |= S_NOCMTIME;
573 #ifdef CONFIG_FS_POSIX_ACL
574         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
575 #endif
576 
577         ovl_lockdep_annotate_inode_mutex_key(inode);
578 
579         switch (mode & S_IFMT) {
580         case S_IFREG:
581                 inode->i_op = &ovl_file_inode_operations;
582                 inode->i_fop = &ovl_file_operations;
583                 inode->i_mapping->a_ops = &ovl_aops;
584                 break;
585 
586         case S_IFDIR:
587                 inode->i_op = &ovl_dir_inode_operations;
588                 inode->i_fop = &ovl_dir_operations;
589                 break;
590 
591         case S_IFLNK:
592                 inode->i_op = &ovl_symlink_inode_operations;
593                 break;
594 
595         default:
596                 inode->i_op = &ovl_special_inode_operations;
597                 init_special_inode(inode, mode, rdev);
598                 break;
599         }
600 }
601 
602 /*
603  * With inodes index enabled, an overlay inode nlink counts the union of upper
604  * hardlinks and non-covered lower hardlinks. During the lifetime of a non-pure
605  * upper inode, the following nlink modifying operations can happen:
606  *
607  * 1. Lower hardlink copy up
608  * 2. Upper hardlink created, unlinked or renamed over
609  * 3. Lower hardlink whiteout or renamed over
610  *
611  * For the first, copy up case, the union nlink does not change, whether the
612  * operation succeeds or fails, but the upper inode nlink may change.
613  * Therefore, before copy up, we store the union nlink value relative to the
614  * lower inode nlink in the index inode xattr trusted.overlay.nlink.
615  *
616  * For the second, upper hardlink case, the union nlink should be incremented
617  * or decremented IFF the operation succeeds, aligned with nlink change of the
618  * upper inode. Therefore, before link/unlink/rename, we store the union nlink
619  * value relative to the upper inode nlink in the index inode.
620  *
621  * For the last, lower cover up case, we simplify things by preceding the
622  * whiteout or cover up with copy up. This makes sure that there is an index
623  * upper inode where the nlink xattr can be stored before the copied up upper
624  * entry is unlink.
625  */
626 #define OVL_NLINK_ADD_UPPER     (1 << 0)
627 
628 /*
629  * On-disk format for indexed nlink:
630  *
631  * nlink relative to the upper inode - "U[+-]NUM"
632  * nlink relative to the lower inode - "L[+-]NUM"
633  */
634 
635 static int ovl_set_nlink_common(struct dentry *dentry,
636                                 struct dentry *realdentry, const char *format)
637 {
638         struct inode *inode = d_inode(dentry);
639         struct inode *realinode = d_inode(realdentry);
640         char buf[13];
641         int len;
642 
643         len = snprintf(buf, sizeof(buf), format,
644                        (int) (inode->i_nlink - realinode->i_nlink));
645 
646         if (WARN_ON(len >= sizeof(buf)))
647                 return -EIO;
648 
649         return ovl_do_setxattr(ovl_dentry_upper(dentry),
650                                OVL_XATTR_NLINK, buf, len, 0);
651 }
652 
653 int ovl_set_nlink_upper(struct dentry *dentry)
654 {
655         return ovl_set_nlink_common(dentry, ovl_dentry_upper(dentry), "U%+i");
656 }
657 
658 int ovl_set_nlink_lower(struct dentry *dentry)
659 {
660         return ovl_set_nlink_common(dentry, ovl_dentry_lower(dentry), "L%+i");
661 }
662 
663 unsigned int ovl_get_nlink(struct dentry *lowerdentry,
664                            struct dentry *upperdentry,
665                            unsigned int fallback)
666 {
667         int nlink_diff;
668         int nlink;
669         char buf[13];
670         int err;
671 
672         if (!lowerdentry || !upperdentry || d_inode(lowerdentry)->i_nlink == 1)
673                 return fallback;
674 
675         err = vfs_getxattr(upperdentry, OVL_XATTR_NLINK, &buf, sizeof(buf) - 1);
676         if (err < 0)
677                 goto fail;
678 
679         buf[err] = '\0';
680         if ((buf[0] != 'L' && buf[0] != 'U') ||
681             (buf[1] != '+' && buf[1] != '-'))
682                 goto fail;
683 
684         err = kstrtoint(buf + 1, 10, &nlink_diff);
685         if (err < 0)
686                 goto fail;
687 
688         nlink = d_inode(buf[0] == 'L' ? lowerdentry : upperdentry)->i_nlink;
689         nlink += nlink_diff;
690 
691         if (nlink <= 0)
692                 goto fail;
693 
694         return nlink;
695 
696 fail:
697         pr_warn_ratelimited("overlayfs: failed to get index nlink (%pd2, err=%i)\n",
698                             upperdentry, err);
699         return fallback;
700 }
701 
702 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
703 {
704         struct inode *inode;
705 
706         inode = new_inode(sb);
707         if (inode)
708                 ovl_fill_inode(inode, mode, rdev, 0, 0);
709 
710         return inode;
711 }
712 
713 static int ovl_inode_test(struct inode *inode, void *data)
714 {
715         return inode->i_private == data;
716 }
717 
718 static int ovl_inode_set(struct inode *inode, void *data)
719 {
720         inode->i_private = data;
721         return 0;
722 }
723 
724 static bool ovl_verify_inode(struct inode *inode, struct dentry *lowerdentry,
725                              struct dentry *upperdentry, bool strict)
726 {
727         /*
728          * For directories, @strict verify from lookup path performs consistency
729          * checks, so NULL lower/upper in dentry must match NULL lower/upper in
730          * inode. Non @strict verify from NFS handle decode path passes NULL for
731          * 'unknown' lower/upper.
732          */
733         if (S_ISDIR(inode->i_mode) && strict) {
734                 /* Real lower dir moved to upper layer under us? */
735                 if (!lowerdentry && ovl_inode_lower(inode))
736                         return false;
737 
738                 /* Lookup of an uncovered redirect origin? */
739                 if (!upperdentry && ovl_inode_upper(inode))
740                         return false;
741         }
742 
743         /*
744          * Allow non-NULL lower inode in ovl_inode even if lowerdentry is NULL.
745          * This happens when finding a copied up overlay inode for a renamed
746          * or hardlinked overlay dentry and lower dentry cannot be followed
747          * by origin because lower fs does not support file handles.
748          */
749         if (lowerdentry && ovl_inode_lower(inode) != d_inode(lowerdentry))
750                 return false;
751 
752         /*
753          * Allow non-NULL __upperdentry in inode even if upperdentry is NULL.
754          * This happens when finding a lower alias for a copied up hard link.
755          */
756         if (upperdentry && ovl_inode_upper(inode) != d_inode(upperdentry))
757                 return false;
758 
759         return true;
760 }
761 
762 struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
763                                bool is_upper)
764 {
765         struct inode *inode, *key = d_inode(real);
766 
767         inode = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
768         if (!inode)
769                 return NULL;
770 
771         if (!ovl_verify_inode(inode, is_upper ? NULL : real,
772                               is_upper ? real : NULL, false)) {
773                 iput(inode);
774                 return ERR_PTR(-ESTALE);
775         }
776 
777         return inode;
778 }
779 
780 /*
781  * Does overlay inode need to be hashed by lower inode?
782  */
783 static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
784                              struct dentry *lower, struct dentry *index)
785 {
786         struct ovl_fs *ofs = sb->s_fs_info;
787 
788         /* No, if pure upper */
789         if (!lower)
790                 return false;
791 
792         /* Yes, if already indexed */
793         if (index)
794                 return true;
795 
796         /* Yes, if won't be copied up */
797         if (!ofs->upper_mnt)
798                 return true;
799 
800         /* No, if lower hardlink is or will be broken on copy up */
801         if ((upper || !ovl_indexdir(sb)) &&
802             !d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
803                 return false;
804 
805         /* No, if non-indexed upper with NFS export */
806         if (sb->s_export_op && upper)
807                 return false;
808 
809         /* Otherwise, hash by lower inode for fsnotify */
810         return true;
811 }
812 
813 static struct inode *ovl_iget5(struct super_block *sb, struct inode *newinode,
814                                struct inode *key)
815 {
816         return newinode ? inode_insert5(newinode, (unsigned long) key,
817                                          ovl_inode_test, ovl_inode_set, key) :
818                           iget5_locked(sb, (unsigned long) key,
819                                        ovl_inode_test, ovl_inode_set, key);
820 }
821 
822 struct inode *ovl_get_inode(struct super_block *sb,
823                             struct ovl_inode_params *oip)
824 {
825         struct dentry *upperdentry = oip->upperdentry;
826         struct ovl_path *lowerpath = oip->lowerpath;
827         struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
828         struct inode *inode;
829         struct dentry *lowerdentry = lowerpath ? lowerpath->dentry : NULL;
830         bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry,
831                                         oip->index);
832         int fsid = bylower ? oip->lowerpath->layer->fsid : 0;
833         bool is_dir, metacopy = false;
834         unsigned long ino = 0;
835         int err = -ENOMEM;
836 
837         if (!realinode)
838                 realinode = d_inode(lowerdentry);
839 
840         /*
841          * Copy up origin (lower) may exist for non-indexed upper, but we must
842          * not use lower as hash key if this is a broken hardlink.
843          */
844         is_dir = S_ISDIR(realinode->i_mode);
845         if (upperdentry || bylower) {
846                 struct inode *key = d_inode(bylower ? lowerdentry :
847                                                       upperdentry);
848                 unsigned int nlink = is_dir ? 1 : realinode->i_nlink;
849 
850                 inode = ovl_iget5(sb, oip->newinode, key);
851                 if (!inode)
852                         goto out_err;
853                 if (!(inode->i_state & I_NEW)) {
854                         /*
855                          * Verify that the underlying files stored in the inode
856                          * match those in the dentry.
857                          */
858                         if (!ovl_verify_inode(inode, lowerdentry, upperdentry,
859                                               true)) {
860                                 iput(inode);
861                                 err = -ESTALE;
862                                 goto out_err;
863                         }
864 
865                         dput(upperdentry);
866                         kfree(oip->redirect);
867                         goto out;
868                 }
869 
870                 /* Recalculate nlink for non-dir due to indexing */
871                 if (!is_dir)
872                         nlink = ovl_get_nlink(lowerdentry, upperdentry, nlink);
873                 set_nlink(inode, nlink);
874                 ino = key->i_ino;
875         } else {
876                 /* Lower hardlink that will be broken on copy up */
877                 inode = new_inode(sb);
878                 if (!inode) {
879                         err = -ENOMEM;
880                         goto out_err;
881                 }
882         }
883         ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev, ino, fsid);
884         ovl_inode_init(inode, upperdentry, lowerdentry, oip->lowerdata);
885 
886         if (upperdentry && ovl_is_impuredir(upperdentry))
887                 ovl_set_flag(OVL_IMPURE, inode);
888 
889         if (oip->index)
890                 ovl_set_flag(OVL_INDEX, inode);
891 
892         if (upperdentry) {
893                 err = ovl_check_metacopy_xattr(upperdentry);
894                 if (err < 0)
895                         goto out_err;
896                 metacopy = err;
897                 if (!metacopy)
898                         ovl_set_flag(OVL_UPPERDATA, inode);
899         }
900 
901         OVL_I(inode)->redirect = oip->redirect;
902 
903         if (bylower)
904                 ovl_set_flag(OVL_CONST_INO, inode);
905 
906         /* Check for non-merge dir that may have whiteouts */
907         if (is_dir) {
908                 if (((upperdentry && lowerdentry) || oip->numlower > 1) ||
909                     ovl_check_origin_xattr(upperdentry ?: lowerdentry)) {
910                         ovl_set_flag(OVL_WHITEOUTS, inode);
911                 }
912         }
913 
914         if (inode->i_state & I_NEW)
915                 unlock_new_inode(inode);
916 out:
917         return inode;
918 
919 out_err:
920         inode = ERR_PTR(err);
921         goto out;
922 }
923 

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