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

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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/namei.h>
 13 #include <linux/file.h>
 14 #include <linux/xattr.h>
 15 #include <linux/rbtree.h>
 16 #include <linux/security.h>
 17 #include <linux/cred.h>
 18 #include "overlayfs.h"
 19 
 20 struct ovl_cache_entry {
 21         unsigned int len;
 22         unsigned int type;
 23         u64 ino;
 24         struct list_head l_node;
 25         struct rb_node node;
 26         struct ovl_cache_entry *next_maybe_whiteout;
 27         bool is_whiteout;
 28         char name[];
 29 };
 30 
 31 struct ovl_dir_cache {
 32         long refcount;
 33         u64 version;
 34         struct list_head entries;
 35 };
 36 
 37 struct ovl_readdir_data {
 38         struct dir_context ctx;
 39         bool is_lowest;
 40         struct rb_root root;
 41         struct list_head *list;
 42         struct list_head middle;
 43         struct ovl_cache_entry *first_maybe_whiteout;
 44         int count;
 45         int err;
 46         bool d_type_supported;
 47 };
 48 
 49 struct ovl_dir_file {
 50         bool is_real;
 51         bool is_upper;
 52         struct ovl_dir_cache *cache;
 53         struct list_head *cursor;
 54         struct file *realfile;
 55         struct file *upperfile;
 56 };
 57 
 58 static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
 59 {
 60         return container_of(n, struct ovl_cache_entry, node);
 61 }
 62 
 63 static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
 64                                                     const char *name, int len)
 65 {
 66         struct rb_node *node = root->rb_node;
 67         int cmp;
 68 
 69         while (node) {
 70                 struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
 71 
 72                 cmp = strncmp(name, p->name, len);
 73                 if (cmp > 0)
 74                         node = p->node.rb_right;
 75                 else if (cmp < 0 || len < p->len)
 76                         node = p->node.rb_left;
 77                 else
 78                         return p;
 79         }
 80 
 81         return NULL;
 82 }
 83 
 84 static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
 85                                                    const char *name, int len,
 86                                                    u64 ino, unsigned int d_type)
 87 {
 88         struct ovl_cache_entry *p;
 89         size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);
 90 
 91         p = kmalloc(size, GFP_KERNEL);
 92         if (!p)
 93                 return NULL;
 94 
 95         memcpy(p->name, name, len);
 96         p->name[len] = '\0';
 97         p->len = len;
 98         p->type = d_type;
 99         p->ino = ino;
100         p->is_whiteout = false;
101 
102         if (d_type == DT_CHR) {
103                 p->next_maybe_whiteout = rdd->first_maybe_whiteout;
104                 rdd->first_maybe_whiteout = p;
105         }
106         return p;
107 }
108 
109 static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
110                                   const char *name, int len, u64 ino,
111                                   unsigned int d_type)
112 {
113         struct rb_node **newp = &rdd->root.rb_node;
114         struct rb_node *parent = NULL;
115         struct ovl_cache_entry *p;
116 
117         while (*newp) {
118                 int cmp;
119                 struct ovl_cache_entry *tmp;
120 
121                 parent = *newp;
122                 tmp = ovl_cache_entry_from_node(*newp);
123                 cmp = strncmp(name, tmp->name, len);
124                 if (cmp > 0)
125                         newp = &tmp->node.rb_right;
126                 else if (cmp < 0 || len < tmp->len)
127                         newp = &tmp->node.rb_left;
128                 else
129                         return 0;
130         }
131 
132         p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
133         if (p == NULL)
134                 return -ENOMEM;
135 
136         list_add_tail(&p->l_node, rdd->list);
137         rb_link_node(&p->node, parent, newp);
138         rb_insert_color(&p->node, &rdd->root);
139 
140         return 0;
141 }
142 
143 static int ovl_fill_lowest(struct ovl_readdir_data *rdd,
144                            const char *name, int namelen,
145                            loff_t offset, u64 ino, unsigned int d_type)
146 {
147         struct ovl_cache_entry *p;
148 
149         p = ovl_cache_entry_find(&rdd->root, name, namelen);
150         if (p) {
151                 list_move_tail(&p->l_node, &rdd->middle);
152         } else {
153                 p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
154                 if (p == NULL)
155                         rdd->err = -ENOMEM;
156                 else
157                         list_add_tail(&p->l_node, &rdd->middle);
158         }
159 
160         return rdd->err;
161 }
162 
163 void ovl_cache_free(struct list_head *list)
164 {
165         struct ovl_cache_entry *p;
166         struct ovl_cache_entry *n;
167 
168         list_for_each_entry_safe(p, n, list, l_node)
169                 kfree(p);
170 
171         INIT_LIST_HEAD(list);
172 }
173 
174 static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
175 {
176         struct ovl_dir_cache *cache = od->cache;
177 
178         WARN_ON(cache->refcount <= 0);
179         cache->refcount--;
180         if (!cache->refcount) {
181                 if (ovl_dir_cache(dentry) == cache)
182                         ovl_set_dir_cache(dentry, NULL);
183 
184                 ovl_cache_free(&cache->entries);
185                 kfree(cache);
186         }
187 }
188 
189 static int ovl_fill_merge(struct dir_context *ctx, const char *name,
190                           int namelen, loff_t offset, u64 ino,
191                           unsigned int d_type)
192 {
193         struct ovl_readdir_data *rdd =
194                 container_of(ctx, struct ovl_readdir_data, ctx);
195 
196         rdd->count++;
197         if (!rdd->is_lowest)
198                 return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
199         else
200                 return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
201 }
202 
203 static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
204 {
205         int err;
206         struct ovl_cache_entry *p;
207         struct dentry *dentry;
208         const struct cred *old_cred;
209         struct cred *override_cred;
210 
211         override_cred = prepare_creds();
212         if (!override_cred)
213                 return -ENOMEM;
214 
215         /*
216          * CAP_DAC_OVERRIDE for lookup
217          */
218         cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
219         old_cred = override_creds(override_cred);
220 
221         err = mutex_lock_killable(&dir->d_inode->i_mutex);
222         if (!err) {
223                 while (rdd->first_maybe_whiteout) {
224                         p = rdd->first_maybe_whiteout;
225                         rdd->first_maybe_whiteout = p->next_maybe_whiteout;
226                         dentry = lookup_one_len(p->name, dir, p->len);
227                         if (!IS_ERR(dentry)) {
228                                 p->is_whiteout = ovl_is_whiteout(dentry);
229                                 dput(dentry);
230                         }
231                 }
232                 inode_unlock(dir->d_inode);
233         }
234         revert_creds(old_cred);
235         put_cred(override_cred);
236 
237         return err;
238 }
239 
240 static inline int ovl_dir_read(struct path *realpath,
241                                struct ovl_readdir_data *rdd)
242 {
243         struct file *realfile;
244         int err;
245 
246         realfile = ovl_path_open(realpath, O_RDONLY | O_DIRECTORY);
247         if (IS_ERR(realfile))
248                 return PTR_ERR(realfile);
249 
250         rdd->first_maybe_whiteout = NULL;
251         rdd->ctx.pos = 0;
252         do {
253                 rdd->count = 0;
254                 rdd->err = 0;
255                 err = iterate_dir(realfile, &rdd->ctx);
256                 if (err >= 0)
257                         err = rdd->err;
258         } while (!err && rdd->count);
259 
260         if (!err && rdd->first_maybe_whiteout)
261                 err = ovl_check_whiteouts(realpath->dentry, rdd);
262 
263         fput(realfile);
264 
265         return err;
266 }
267 
268 static void ovl_dir_reset(struct file *file)
269 {
270         struct ovl_dir_file *od = file->private_data;
271         struct ovl_dir_cache *cache = od->cache;
272         struct dentry *dentry = file->f_path.dentry;
273         enum ovl_path_type type = ovl_path_type(dentry);
274 
275         if (cache && ovl_dentry_version_get(dentry) != cache->version) {
276                 ovl_cache_put(od, dentry);
277                 od->cache = NULL;
278                 od->cursor = NULL;
279         }
280         WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
281         if (od->is_real && OVL_TYPE_MERGE(type))
282                 od->is_real = false;
283 }
284 
285 static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
286 {
287         int err;
288         struct path realpath;
289         struct ovl_readdir_data rdd = {
290                 .ctx.actor = ovl_fill_merge,
291                 .list = list,
292                 .root = RB_ROOT,
293                 .is_lowest = false,
294         };
295         int idx, next;
296 
297         for (idx = 0; idx != -1; idx = next) {
298                 next = ovl_path_next(idx, dentry, &realpath);
299 
300                 if (next != -1) {
301                         err = ovl_dir_read(&realpath, &rdd);
302                         if (err)
303                                 break;
304                 } else {
305                         /*
306                          * Insert lowest layer entries before upper ones, this
307                          * allows offsets to be reasonably constant
308                          */
309                         list_add(&rdd.middle, rdd.list);
310                         rdd.is_lowest = true;
311                         err = ovl_dir_read(&realpath, &rdd);
312                         list_del(&rdd.middle);
313                 }
314         }
315         return err;
316 }
317 
318 static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
319 {
320         struct list_head *p;
321         loff_t off = 0;
322 
323         list_for_each(p, &od->cache->entries) {
324                 if (off >= pos)
325                         break;
326                 off++;
327         }
328         /* Cursor is safe since the cache is stable */
329         od->cursor = p;
330 }
331 
332 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
333 {
334         int res;
335         struct ovl_dir_cache *cache;
336 
337         cache = ovl_dir_cache(dentry);
338         if (cache && ovl_dentry_version_get(dentry) == cache->version) {
339                 cache->refcount++;
340                 return cache;
341         }
342         ovl_set_dir_cache(dentry, NULL);
343 
344         cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
345         if (!cache)
346                 return ERR_PTR(-ENOMEM);
347 
348         cache->refcount = 1;
349         INIT_LIST_HEAD(&cache->entries);
350 
351         res = ovl_dir_read_merged(dentry, &cache->entries);
352         if (res) {
353                 ovl_cache_free(&cache->entries);
354                 kfree(cache);
355                 return ERR_PTR(res);
356         }
357 
358         cache->version = ovl_dentry_version_get(dentry);
359         ovl_set_dir_cache(dentry, cache);
360 
361         return cache;
362 }
363 
364 static int ovl_iterate(struct file *file, struct dir_context *ctx)
365 {
366         struct ovl_dir_file *od = file->private_data;
367         struct dentry *dentry = file->f_path.dentry;
368         struct ovl_cache_entry *p;
369 
370         if (!ctx->pos)
371                 ovl_dir_reset(file);
372 
373         if (od->is_real)
374                 return iterate_dir(od->realfile, ctx);
375 
376         if (!od->cache) {
377                 struct ovl_dir_cache *cache;
378 
379                 cache = ovl_cache_get(dentry);
380                 if (IS_ERR(cache))
381                         return PTR_ERR(cache);
382 
383                 od->cache = cache;
384                 ovl_seek_cursor(od, ctx->pos);
385         }
386 
387         while (od->cursor != &od->cache->entries) {
388                 p = list_entry(od->cursor, struct ovl_cache_entry, l_node);
389                 if (!p->is_whiteout)
390                         if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
391                                 break;
392                 od->cursor = p->l_node.next;
393                 ctx->pos++;
394         }
395         return 0;
396 }
397 
398 static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
399 {
400         loff_t res;
401         struct ovl_dir_file *od = file->private_data;
402 
403         inode_lock(file_inode(file));
404         if (!file->f_pos)
405                 ovl_dir_reset(file);
406 
407         if (od->is_real) {
408                 res = vfs_llseek(od->realfile, offset, origin);
409                 file->f_pos = od->realfile->f_pos;
410         } else {
411                 res = -EINVAL;
412 
413                 switch (origin) {
414                 case SEEK_CUR:
415                         offset += file->f_pos;
416                         break;
417                 case SEEK_SET:
418                         break;
419                 default:
420                         goto out_unlock;
421                 }
422                 if (offset < 0)
423                         goto out_unlock;
424 
425                 if (offset != file->f_pos) {
426                         file->f_pos = offset;
427                         if (od->cache)
428                                 ovl_seek_cursor(od, offset);
429                 }
430                 res = offset;
431         }
432 out_unlock:
433         inode_unlock(file_inode(file));
434 
435         return res;
436 }
437 
438 static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
439                          int datasync)
440 {
441         struct ovl_dir_file *od = file->private_data;
442         struct dentry *dentry = file->f_path.dentry;
443         struct file *realfile = od->realfile;
444 
445         /*
446          * Need to check if we started out being a lower dir, but got copied up
447          */
448         if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
449                 struct inode *inode = file_inode(file);
450 
451                 realfile = lockless_dereference(od->upperfile);
452                 if (!realfile) {
453                         struct path upperpath;
454 
455                         ovl_path_upper(dentry, &upperpath);
456                         realfile = ovl_path_open(&upperpath, O_RDONLY);
457                         smp_mb__before_spinlock();
458                         inode_lock(inode);
459                         if (!od->upperfile) {
460                                 if (IS_ERR(realfile)) {
461                                         inode_unlock(inode);
462                                         return PTR_ERR(realfile);
463                                 }
464                                 od->upperfile = realfile;
465                         } else {
466                                 /* somebody has beaten us to it */
467                                 if (!IS_ERR(realfile))
468                                         fput(realfile);
469                                 realfile = od->upperfile;
470                         }
471                         inode_unlock(inode);
472                 }
473         }
474 
475         return vfs_fsync_range(realfile, start, end, datasync);
476 }
477 
478 static int ovl_dir_release(struct inode *inode, struct file *file)
479 {
480         struct ovl_dir_file *od = file->private_data;
481 
482         if (od->cache) {
483                 inode_lock(inode);
484                 ovl_cache_put(od, file->f_path.dentry);
485                 inode_unlock(inode);
486         }
487         fput(od->realfile);
488         if (od->upperfile)
489                 fput(od->upperfile);
490         kfree(od);
491 
492         return 0;
493 }
494 
495 static int ovl_dir_open(struct inode *inode, struct file *file)
496 {
497         struct path realpath;
498         struct file *realfile;
499         struct ovl_dir_file *od;
500         enum ovl_path_type type;
501 
502         od = kzalloc(sizeof(struct ovl_dir_file), GFP_KERNEL);
503         if (!od)
504                 return -ENOMEM;
505 
506         type = ovl_path_real(file->f_path.dentry, &realpath);
507         realfile = ovl_path_open(&realpath, file->f_flags);
508         if (IS_ERR(realfile)) {
509                 kfree(od);
510                 return PTR_ERR(realfile);
511         }
512         od->realfile = realfile;
513         od->is_real = !OVL_TYPE_MERGE(type);
514         od->is_upper = OVL_TYPE_UPPER(type);
515         file->private_data = od;
516 
517         return 0;
518 }
519 
520 const struct file_operations ovl_dir_operations = {
521         .read           = generic_read_dir,
522         .open           = ovl_dir_open,
523         .iterate        = ovl_iterate,
524         .llseek         = ovl_dir_llseek,
525         .fsync          = ovl_dir_fsync,
526         .release        = ovl_dir_release,
527 };
528 
529 int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
530 {
531         int err;
532         struct ovl_cache_entry *p;
533 
534         err = ovl_dir_read_merged(dentry, list);
535         if (err)
536                 return err;
537 
538         err = 0;
539 
540         list_for_each_entry(p, list, l_node) {
541                 if (p->is_whiteout)
542                         continue;
543 
544                 if (p->name[0] == '.') {
545                         if (p->len == 1)
546                                 continue;
547                         if (p->len == 2 && p->name[1] == '.')
548                                 continue;
549                 }
550                 err = -ENOTEMPTY;
551                 break;
552         }
553 
554         return err;
555 }
556 
557 void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
558 {
559         struct ovl_cache_entry *p;
560 
561         inode_lock_nested(upper->d_inode, I_MUTEX_CHILD);
562         list_for_each_entry(p, list, l_node) {
563                 struct dentry *dentry;
564 
565                 if (!p->is_whiteout)
566                         continue;
567 
568                 dentry = lookup_one_len(p->name, upper, p->len);
569                 if (IS_ERR(dentry)) {
570                         pr_err("overlayfs: lookup '%s/%.*s' failed (%i)\n",
571                                upper->d_name.name, p->len, p->name,
572                                (int) PTR_ERR(dentry));
573                         continue;
574                 }
575                 if (dentry->d_inode)
576                         ovl_cleanup(upper->d_inode, dentry);
577                 dput(dentry);
578         }
579         inode_unlock(upper->d_inode);
580 }
581 
582 static int ovl_check_d_type(struct dir_context *ctx, const char *name,
583                           int namelen, loff_t offset, u64 ino,
584                           unsigned int d_type)
585 {
586         struct ovl_readdir_data *rdd =
587                 container_of(ctx, struct ovl_readdir_data, ctx);
588 
589         /* Even if d_type is not supported, DT_DIR is returned for . and .. */
590         if (!strncmp(name, ".", namelen) || !strncmp(name, "..", namelen))
591                 return 0;
592 
593         if (d_type != DT_UNKNOWN)
594                 rdd->d_type_supported = true;
595 
596         return 0;
597 }
598 
599 /*
600  * Returns 1 if d_type is supported, 0 not supported/unknown. Negative values
601  * if error is encountered.
602  */
603 int ovl_check_d_type_supported(struct path *realpath)
604 {
605         int err;
606         struct ovl_readdir_data rdd = {
607                 .ctx.actor = ovl_check_d_type,
608                 .d_type_supported = false,
609         };
610 
611         err = ovl_dir_read(realpath, &rdd);
612         if (err)
613                 return err;
614 
615         return rdd.d_type_supported;
616 }
617 

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