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Linux/fs/exportfs/expfs.c

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  1 /*
  2  * Copyright (C) Neil Brown 2002
  3  * Copyright (C) Christoph Hellwig 2007
  4  *
  5  * This file contains the code mapping from inodes to NFS file handles,
  6  * and for mapping back from file handles to dentries.
  7  *
  8  * For details on why we do all the strange and hairy things in here
  9  * take a look at Documentation/filesystems/nfs/Exporting.
 10  */
 11 #include <linux/exportfs.h>
 12 #include <linux/fs.h>
 13 #include <linux/file.h>
 14 #include <linux/module.h>
 15 #include <linux/mount.h>
 16 #include <linux/namei.h>
 17 #include <linux/sched.h>
 18 
 19 #define dprintk(fmt, args...) do{}while(0)
 20 
 21 
 22 static int get_name(const struct path *path, char *name, struct dentry *child);
 23 
 24 
 25 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
 26                 char *name, struct dentry *child)
 27 {
 28         const struct export_operations *nop = dir->d_sb->s_export_op;
 29         struct path path = {.mnt = mnt, .dentry = dir};
 30 
 31         if (nop->get_name)
 32                 return nop->get_name(dir, name, child);
 33         else
 34                 return get_name(&path, name, child);
 35 }
 36 
 37 /*
 38  * Check if the dentry or any of it's aliases is acceptable.
 39  */
 40 static struct dentry *
 41 find_acceptable_alias(struct dentry *result,
 42                 int (*acceptable)(void *context, struct dentry *dentry),
 43                 void *context)
 44 {
 45         struct dentry *dentry, *toput = NULL;
 46         struct inode *inode;
 47 
 48         if (acceptable(context, result))
 49                 return result;
 50 
 51         inode = result->d_inode;
 52         spin_lock(&inode->i_lock);
 53         hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
 54                 dget(dentry);
 55                 spin_unlock(&inode->i_lock);
 56                 if (toput)
 57                         dput(toput);
 58                 if (dentry != result && acceptable(context, dentry)) {
 59                         dput(result);
 60                         return dentry;
 61                 }
 62                 spin_lock(&inode->i_lock);
 63                 toput = dentry;
 64         }
 65         spin_unlock(&inode->i_lock);
 66 
 67         if (toput)
 68                 dput(toput);
 69         return NULL;
 70 }
 71 
 72 static bool dentry_connected(struct dentry *dentry)
 73 {
 74         dget(dentry);
 75         while (dentry->d_flags & DCACHE_DISCONNECTED) {
 76                 struct dentry *parent = dget_parent(dentry);
 77 
 78                 dput(dentry);
 79                 if (dentry == parent) {
 80                         dput(parent);
 81                         return false;
 82                 }
 83                 dentry = parent;
 84         }
 85         dput(dentry);
 86         return true;
 87 }
 88 
 89 static void clear_disconnected(struct dentry *dentry)
 90 {
 91         dget(dentry);
 92         while (dentry->d_flags & DCACHE_DISCONNECTED) {
 93                 struct dentry *parent = dget_parent(dentry);
 94 
 95                 WARN_ON_ONCE(IS_ROOT(dentry));
 96 
 97                 spin_lock(&dentry->d_lock);
 98                 dentry->d_flags &= ~DCACHE_DISCONNECTED;
 99                 spin_unlock(&dentry->d_lock);
100 
101                 dput(dentry);
102                 dentry = parent;
103         }
104         dput(dentry);
105 }
106 
107 /*
108  * Reconnect a directory dentry with its parent.
109  *
110  * This can return a dentry, or NULL, or an error.
111  *
112  * In the first case the returned dentry is the parent of the given
113  * dentry, and may itself need to be reconnected to its parent.
114  *
115  * In the NULL case, a concurrent VFS operation has either renamed or
116  * removed this directory.  The concurrent operation has reconnected our
117  * dentry, so we no longer need to.
118  */
119 static struct dentry *reconnect_one(struct vfsmount *mnt,
120                 struct dentry *dentry, char *nbuf)
121 {
122         struct dentry *parent;
123         struct dentry *tmp;
124         int err;
125 
126         parent = ERR_PTR(-EACCES);
127         mutex_lock(&dentry->d_inode->i_mutex);
128         if (mnt->mnt_sb->s_export_op->get_parent)
129                 parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
130         mutex_unlock(&dentry->d_inode->i_mutex);
131 
132         if (IS_ERR(parent)) {
133                 dprintk("%s: get_parent of %ld failed, err %d\n",
134                         __func__, dentry->d_inode->i_ino, PTR_ERR(parent));
135                 return parent;
136         }
137 
138         dprintk("%s: find name of %lu in %lu\n", __func__,
139                 dentry->d_inode->i_ino, parent->d_inode->i_ino);
140         err = exportfs_get_name(mnt, parent, nbuf, dentry);
141         if (err == -ENOENT)
142                 goto out_reconnected;
143         if (err)
144                 goto out_err;
145         dprintk("%s: found name: %s\n", __func__, nbuf);
146         mutex_lock(&parent->d_inode->i_mutex);
147         tmp = lookup_one_len(nbuf, parent, strlen(nbuf));
148         mutex_unlock(&parent->d_inode->i_mutex);
149         if (IS_ERR(tmp)) {
150                 dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
151                 goto out_err;
152         }
153         if (tmp != dentry) {
154                 dput(tmp);
155                 goto out_reconnected;
156         }
157         dput(tmp);
158         if (IS_ROOT(dentry)) {
159                 err = -ESTALE;
160                 goto out_err;
161         }
162         return parent;
163 
164 out_err:
165         dput(parent);
166         return ERR_PTR(err);
167 out_reconnected:
168         dput(parent);
169         /*
170          * Someone must have renamed our entry into another parent, in
171          * which case it has been reconnected by the rename.
172          *
173          * Or someone removed it entirely, in which case filehandle
174          * lookup will succeed but the directory is now IS_DEAD and
175          * subsequent operations on it will fail.
176          *
177          * Alternatively, maybe there was no race at all, and the
178          * filesystem is just corrupt and gave us a parent that doesn't
179          * actually contain any entry pointing to this inode.  So,
180          * double check that this worked and return -ESTALE if not:
181          */
182         if (!dentry_connected(dentry))
183                 return ERR_PTR(-ESTALE);
184         return NULL;
185 }
186 
187 /*
188  * Make sure target_dir is fully connected to the dentry tree.
189  *
190  * On successful return, DCACHE_DISCONNECTED will be cleared on
191  * target_dir, and target_dir->d_parent->...->d_parent will reach the
192  * root of the filesystem.
193  *
194  * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
195  * But the converse is not true: target_dir may have DCACHE_DISCONNECTED
196  * set but already be connected.  In that case we'll verify the
197  * connection to root and then clear the flag.
198  *
199  * Note that target_dir could be removed by a concurrent operation.  In
200  * that case reconnect_path may still succeed with target_dir fully
201  * connected, but further operations using the filehandle will fail when
202  * necessary (due to S_DEAD being set on the directory).
203  */
204 static int
205 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
206 {
207         struct dentry *dentry, *parent;
208 
209         dentry = dget(target_dir);
210 
211         while (dentry->d_flags & DCACHE_DISCONNECTED) {
212                 BUG_ON(dentry == mnt->mnt_sb->s_root);
213 
214                 if (IS_ROOT(dentry))
215                         parent = reconnect_one(mnt, dentry, nbuf);
216                 else
217                         parent = dget_parent(dentry);
218 
219                 if (!parent)
220                         break;
221                 dput(dentry);
222                 if (IS_ERR(parent))
223                         return PTR_ERR(parent);
224                 dentry = parent;
225         }
226         dput(dentry);
227         clear_disconnected(target_dir);
228         return 0;
229 }
230 
231 struct getdents_callback {
232         struct dir_context ctx;
233         char *name;             /* name that was found. It already points to a
234                                    buffer NAME_MAX+1 is size */
235         u64 ino;                /* the inum we are looking for */
236         int found;              /* inode matched? */
237         int sequence;           /* sequence counter */
238 };
239 
240 /*
241  * A rather strange filldir function to capture
242  * the name matching the specified inode number.
243  */
244 static int filldir_one(void * __buf, const char * name, int len,
245                         loff_t pos, u64 ino, unsigned int d_type)
246 {
247         struct getdents_callback *buf = __buf;
248         int result = 0;
249 
250         buf->sequence++;
251         if (buf->ino == ino && len <= NAME_MAX) {
252                 memcpy(buf->name, name, len);
253                 buf->name[len] = '\0';
254                 buf->found = 1;
255                 result = -1;
256         }
257         return result;
258 }
259 
260 /**
261  * get_name - default export_operations->get_name function
262  * @path:   the directory in which to find a name
263  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
264  * @child:  the dentry for the child directory.
265  *
266  * calls readdir on the parent until it finds an entry with
267  * the same inode number as the child, and returns that.
268  */
269 static int get_name(const struct path *path, char *name, struct dentry *child)
270 {
271         const struct cred *cred = current_cred();
272         struct inode *dir = path->dentry->d_inode;
273         int error;
274         struct file *file;
275         struct kstat stat;
276         struct path child_path = {
277                 .mnt = path->mnt,
278                 .dentry = child,
279         };
280         struct getdents_callback buffer = {
281                 .ctx.actor = filldir_one,
282                 .name = name,
283         };
284 
285         error = -ENOTDIR;
286         if (!dir || !S_ISDIR(dir->i_mode))
287                 goto out;
288         error = -EINVAL;
289         if (!dir->i_fop)
290                 goto out;
291         /*
292          * inode->i_ino is unsigned long, kstat->ino is u64, so the
293          * former would be insufficient on 32-bit hosts when the
294          * filesystem supports 64-bit inode numbers.  So we need to
295          * actually call ->getattr, not just read i_ino:
296          */
297         error = vfs_getattr_nosec(&child_path, &stat);
298         if (error)
299                 return error;
300         buffer.ino = stat.ino;
301         /*
302          * Open the directory ...
303          */
304         file = dentry_open(path, O_RDONLY, cred);
305         error = PTR_ERR(file);
306         if (IS_ERR(file))
307                 goto out;
308 
309         error = -EINVAL;
310         if (!file->f_op->iterate)
311                 goto out_close;
312 
313         buffer.sequence = 0;
314         while (1) {
315                 int old_seq = buffer.sequence;
316 
317                 error = iterate_dir(file, &buffer.ctx);
318                 if (buffer.found) {
319                         error = 0;
320                         break;
321                 }
322 
323                 if (error < 0)
324                         break;
325 
326                 error = -ENOENT;
327                 if (old_seq == buffer.sequence)
328                         break;
329         }
330 
331 out_close:
332         fput(file);
333 out:
334         return error;
335 }
336 
337 /**
338  * export_encode_fh - default export_operations->encode_fh function
339  * @inode:   the object to encode
340  * @fid:     where to store the file handle fragment
341  * @max_len: maximum length to store there
342  * @parent:  parent directory inode, if wanted
343  *
344  * This default encode_fh function assumes that the 32 inode number
345  * is suitable for locating an inode, and that the generation number
346  * can be used to check that it is still valid.  It places them in the
347  * filehandle fragment where export_decode_fh expects to find them.
348  */
349 static int export_encode_fh(struct inode *inode, struct fid *fid,
350                 int *max_len, struct inode *parent)
351 {
352         int len = *max_len;
353         int type = FILEID_INO32_GEN;
354 
355         if (parent && (len < 4)) {
356                 *max_len = 4;
357                 return FILEID_INVALID;
358         } else if (len < 2) {
359                 *max_len = 2;
360                 return FILEID_INVALID;
361         }
362 
363         len = 2;
364         fid->i32.ino = inode->i_ino;
365         fid->i32.gen = inode->i_generation;
366         if (parent) {
367                 fid->i32.parent_ino = parent->i_ino;
368                 fid->i32.parent_gen = parent->i_generation;
369                 len = 4;
370                 type = FILEID_INO32_GEN_PARENT;
371         }
372         *max_len = len;
373         return type;
374 }
375 
376 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
377                              int *max_len, struct inode *parent)
378 {
379         const struct export_operations *nop = inode->i_sb->s_export_op;
380 
381         if (nop && nop->encode_fh)
382                 return nop->encode_fh(inode, fid->raw, max_len, parent);
383 
384         return export_encode_fh(inode, fid, max_len, parent);
385 }
386 EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
387 
388 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
389                 int connectable)
390 {
391         int error;
392         struct dentry *p = NULL;
393         struct inode *inode = dentry->d_inode, *parent = NULL;
394 
395         if (connectable && !S_ISDIR(inode->i_mode)) {
396                 p = dget_parent(dentry);
397                 /*
398                  * note that while p might've ceased to be our parent already,
399                  * it's still pinned by and still positive.
400                  */
401                 parent = p->d_inode;
402         }
403 
404         error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
405         dput(p);
406 
407         return error;
408 }
409 EXPORT_SYMBOL_GPL(exportfs_encode_fh);
410 
411 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
412                 int fh_len, int fileid_type,
413                 int (*acceptable)(void *, struct dentry *), void *context)
414 {
415         const struct export_operations *nop = mnt->mnt_sb->s_export_op;
416         struct dentry *result, *alias;
417         char nbuf[NAME_MAX+1];
418         int err;
419 
420         /*
421          * Try to get any dentry for the given file handle from the filesystem.
422          */
423         if (!nop || !nop->fh_to_dentry)
424                 return ERR_PTR(-ESTALE);
425         result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
426         if (!result)
427                 result = ERR_PTR(-ESTALE);
428         if (IS_ERR(result))
429                 return result;
430 
431         if (S_ISDIR(result->d_inode->i_mode)) {
432                 /*
433                  * This request is for a directory.
434                  *
435                  * On the positive side there is only one dentry for each
436                  * directory inode.  On the negative side this implies that we
437                  * to ensure our dentry is connected all the way up to the
438                  * filesystem root.
439                  */
440                 if (result->d_flags & DCACHE_DISCONNECTED) {
441                         err = reconnect_path(mnt, result, nbuf);
442                         if (err)
443                                 goto err_result;
444                 }
445 
446                 if (!acceptable(context, result)) {
447                         err = -EACCES;
448                         goto err_result;
449                 }
450 
451                 return result;
452         } else {
453                 /*
454                  * It's not a directory.  Life is a little more complicated.
455                  */
456                 struct dentry *target_dir, *nresult;
457 
458                 /*
459                  * See if either the dentry we just got from the filesystem
460                  * or any alias for it is acceptable.  This is always true
461                  * if this filesystem is exported without the subtreecheck
462                  * option.  If the filesystem is exported with the subtree
463                  * check option there's a fair chance we need to look at
464                  * the parent directory in the file handle and make sure
465                  * it's connected to the filesystem root.
466                  */
467                 alias = find_acceptable_alias(result, acceptable, context);
468                 if (alias)
469                         return alias;
470 
471                 /*
472                  * Try to extract a dentry for the parent directory from the
473                  * file handle.  If this fails we'll have to give up.
474                  */
475                 err = -ESTALE;
476                 if (!nop->fh_to_parent)
477                         goto err_result;
478 
479                 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
480                                 fh_len, fileid_type);
481                 if (!target_dir)
482                         goto err_result;
483                 err = PTR_ERR(target_dir);
484                 if (IS_ERR(target_dir))
485                         goto err_result;
486 
487                 /*
488                  * And as usual we need to make sure the parent directory is
489                  * connected to the filesystem root.  The VFS really doesn't
490                  * like disconnected directories..
491                  */
492                 err = reconnect_path(mnt, target_dir, nbuf);
493                 if (err) {
494                         dput(target_dir);
495                         goto err_result;
496                 }
497 
498                 /*
499                  * Now that we've got both a well-connected parent and a
500                  * dentry for the inode we're after, make sure that our
501                  * inode is actually connected to the parent.
502                  */
503                 err = exportfs_get_name(mnt, target_dir, nbuf, result);
504                 if (!err) {
505                         mutex_lock(&target_dir->d_inode->i_mutex);
506                         nresult = lookup_one_len(nbuf, target_dir,
507                                                  strlen(nbuf));
508                         mutex_unlock(&target_dir->d_inode->i_mutex);
509                         if (!IS_ERR(nresult)) {
510                                 if (nresult->d_inode) {
511                                         dput(result);
512                                         result = nresult;
513                                 } else
514                                         dput(nresult);
515                         }
516                 }
517 
518                 /*
519                  * At this point we are done with the parent, but it's pinned
520                  * by the child dentry anyway.
521                  */
522                 dput(target_dir);
523 
524                 /*
525                  * And finally make sure the dentry is actually acceptable
526                  * to NFSD.
527                  */
528                 alias = find_acceptable_alias(result, acceptable, context);
529                 if (!alias) {
530                         err = -EACCES;
531                         goto err_result;
532                 }
533 
534                 return alias;
535         }
536 
537  err_result:
538         dput(result);
539         return ERR_PTR(err);
540 }
541 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
542 
543 MODULE_LICENSE("GPL");
544 

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