Root/fs/exportfs/expfs.c

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
22static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name,
23        struct dentry *child);
24
25
26static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
27        char *name, struct dentry *child)
28{
29    const struct export_operations *nop = dir->d_sb->s_export_op;
30
31    if (nop->get_name)
32        return nop->get_name(dir, name, child);
33    else
34        return get_name(mnt, dir, name, child);
35}
36
37/*
38 * Check if the dentry or any of it's aliases is acceptable.
39 */
40static struct dentry *
41find_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    list_for_each_entry(dentry, &inode->i_dentry, 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/*
73 * Find root of a disconnected subtree and return a reference to it.
74 */
75static struct dentry *
76find_disconnected_root(struct dentry *dentry)
77{
78    dget(dentry);
79    while (!IS_ROOT(dentry)) {
80        struct dentry *parent = dget_parent(dentry);
81
82        if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
83            dput(parent);
84            break;
85        }
86
87        dput(dentry);
88        dentry = parent;
89    }
90    return dentry;
91}
92
93/*
94 * Make sure target_dir is fully connected to the dentry tree.
95 *
96 * It may already be, as the flag isn't always updated when connection happens.
97 */
98static int
99reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
100{
101    int noprogress = 0;
102    int err = -ESTALE;
103
104    /*
105     * It is possible that a confused file system might not let us complete
106     * the path to the root. For example, if get_parent returns a directory
107     * in which we cannot find a name for the child. While this implies a
108     * very sick filesystem we don't want it to cause knfsd to spin. Hence
109     * the noprogress counter. If we go through the loop 10 times (2 is
110     * probably enough) without getting anywhere, we just give up
111     */
112    while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
113        struct dentry *pd = find_disconnected_root(target_dir);
114
115        if (!IS_ROOT(pd)) {
116            /* must have found a connected parent - great */
117            spin_lock(&pd->d_lock);
118            pd->d_flags &= ~DCACHE_DISCONNECTED;
119            spin_unlock(&pd->d_lock);
120            noprogress = 0;
121        } else if (pd == mnt->mnt_sb->s_root) {
122            printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
123            spin_lock(&pd->d_lock);
124            pd->d_flags &= ~DCACHE_DISCONNECTED;
125            spin_unlock(&pd->d_lock);
126            noprogress = 0;
127        } else {
128            /*
129             * We have hit the top of a disconnected path, try to
130             * find parent and connect.
131             *
132             * Racing with some other process renaming a directory
133             * isn't much of a problem here. If someone renames
134             * the directory, it will end up properly connected,
135             * which is what we want
136             *
137             * Getting the parent can't be supported generically,
138             * the locking is too icky.
139             *
140             * Instead we just return EACCES. If server reboots
141             * or inodes get flushed, you lose
142             */
143            struct dentry *ppd = ERR_PTR(-EACCES);
144            struct dentry *npd;
145
146            mutex_lock(&pd->d_inode->i_mutex);
147            if (mnt->mnt_sb->s_export_op->get_parent)
148                ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
149            mutex_unlock(&pd->d_inode->i_mutex);
150
151            if (IS_ERR(ppd)) {
152                err = PTR_ERR(ppd);
153                dprintk("%s: get_parent of %ld failed, err %d\n",
154                    __func__, pd->d_inode->i_ino, err);
155                dput(pd);
156                break;
157            }
158
159            dprintk("%s: find name of %lu in %lu\n", __func__,
160                pd->d_inode->i_ino, ppd->d_inode->i_ino);
161            err = exportfs_get_name(mnt, ppd, nbuf, pd);
162            if (err) {
163                dput(ppd);
164                dput(pd);
165                if (err == -ENOENT)
166                    /* some race between get_parent and
167                     * get_name? just try again
168                     */
169                    continue;
170                break;
171            }
172            dprintk("%s: found name: %s\n", __func__, nbuf);
173            mutex_lock(&ppd->d_inode->i_mutex);
174            npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
175            mutex_unlock(&ppd->d_inode->i_mutex);
176            if (IS_ERR(npd)) {
177                err = PTR_ERR(npd);
178                dprintk("%s: lookup failed: %d\n",
179                    __func__, err);
180                dput(ppd);
181                dput(pd);
182                break;
183            }
184            /* we didn't really want npd, we really wanted
185             * a side-effect of the lookup.
186             * hopefully, npd == pd, though it isn't really
187             * a problem if it isn't
188             */
189            if (npd == pd)
190                noprogress = 0;
191            else
192                printk("%s: npd != pd\n", __func__);
193            dput(npd);
194            dput(ppd);
195            if (IS_ROOT(pd)) {
196                /* something went wrong, we have to give up */
197                dput(pd);
198                break;
199            }
200        }
201        dput(pd);
202    }
203
204    if (target_dir->d_flags & DCACHE_DISCONNECTED) {
205        /* something went wrong - oh-well */
206        if (!err)
207            err = -ESTALE;
208        return err;
209    }
210
211    return 0;
212}
213
214struct getdents_callback {
215    char *name; /* name that was found. It already points to a
216                   buffer NAME_MAX+1 is size */
217    unsigned long ino; /* the inum we are looking for */
218    int found; /* inode matched? */
219    int sequence; /* sequence counter */
220};
221
222/*
223 * A rather strange filldir function to capture
224 * the name matching the specified inode number.
225 */
226static int filldir_one(void * __buf, const char * name, int len,
227            loff_t pos, u64 ino, unsigned int d_type)
228{
229    struct getdents_callback *buf = __buf;
230    int result = 0;
231
232    buf->sequence++;
233    if (buf->ino == ino) {
234        memcpy(buf->name, name, len);
235        buf->name[len] = '\0';
236        buf->found = 1;
237        result = -1;
238    }
239    return result;
240}
241
242/**
243 * get_name - default export_operations->get_name function
244 * @dentry: the directory in which to find a name
245 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name
246 * @child: the dentry for the child directory.
247 *
248 * calls readdir on the parent until it finds an entry with
249 * the same inode number as the child, and returns that.
250 */
251static int get_name(struct vfsmount *mnt, struct dentry *dentry,
252        char *name, struct dentry *child)
253{
254    const struct cred *cred = current_cred();
255    struct inode *dir = dentry->d_inode;
256    int error;
257    struct file *file;
258    struct getdents_callback buffer;
259
260    error = -ENOTDIR;
261    if (!dir || !S_ISDIR(dir->i_mode))
262        goto out;
263    error = -EINVAL;
264    if (!dir->i_fop)
265        goto out;
266    /*
267     * Open the directory ...
268     */
269    file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred);
270    error = PTR_ERR(file);
271    if (IS_ERR(file))
272        goto out;
273
274    error = -EINVAL;
275    if (!file->f_op->readdir)
276        goto out_close;
277
278    buffer.name = name;
279    buffer.ino = child->d_inode->i_ino;
280    buffer.found = 0;
281    buffer.sequence = 0;
282    while (1) {
283        int old_seq = buffer.sequence;
284
285        error = vfs_readdir(file, filldir_one, &buffer);
286        if (buffer.found) {
287            error = 0;
288            break;
289        }
290
291        if (error < 0)
292            break;
293
294        error = -ENOENT;
295        if (old_seq == buffer.sequence)
296            break;
297    }
298
299out_close:
300    fput(file);
301out:
302    return error;
303}
304
305/**
306 * export_encode_fh - default export_operations->encode_fh function
307 * @dentry: the dentry to encode
308 * @fh: where to store the file handle fragment
309 * @max_len: maximum length to store there
310 * @connectable: whether to store parent information
311 *
312 * This default encode_fh function assumes that the 32 inode number
313 * is suitable for locating an inode, and that the generation number
314 * can be used to check that it is still valid. It places them in the
315 * filehandle fragment where export_decode_fh expects to find them.
316 */
317static int export_encode_fh(struct dentry *dentry, struct fid *fid,
318        int *max_len, int connectable)
319{
320    struct inode * inode = dentry->d_inode;
321    int len = *max_len;
322    int type = FILEID_INO32_GEN;
323
324    if (connectable && (len < 4)) {
325        *max_len = 4;
326        return 255;
327    } else if (len < 2) {
328        *max_len = 2;
329        return 255;
330    }
331
332    len = 2;
333    fid->i32.ino = inode->i_ino;
334    fid->i32.gen = inode->i_generation;
335    if (connectable && !S_ISDIR(inode->i_mode)) {
336        struct inode *parent;
337
338        spin_lock(&dentry->d_lock);
339        parent = dentry->d_parent->d_inode;
340        fid->i32.parent_ino = parent->i_ino;
341        fid->i32.parent_gen = parent->i_generation;
342        spin_unlock(&dentry->d_lock);
343        len = 4;
344        type = FILEID_INO32_GEN_PARENT;
345    }
346    *max_len = len;
347    return type;
348}
349
350int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
351        int connectable)
352{
353    const struct export_operations *nop = dentry->d_sb->s_export_op;
354    int error;
355
356    if (nop->encode_fh)
357        error = nop->encode_fh(dentry, fid->raw, max_len, connectable);
358    else
359        error = export_encode_fh(dentry, fid, max_len, connectable);
360
361    return error;
362}
363EXPORT_SYMBOL_GPL(exportfs_encode_fh);
364
365struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
366        int fh_len, int fileid_type,
367        int (*acceptable)(void *, struct dentry *), void *context)
368{
369    const struct export_operations *nop = mnt->mnt_sb->s_export_op;
370    struct dentry *result, *alias;
371    char nbuf[NAME_MAX+1];
372    int err;
373
374    /*
375     * Try to get any dentry for the given file handle from the filesystem.
376     */
377    if (!nop || !nop->fh_to_dentry)
378        return ERR_PTR(-ESTALE);
379    result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
380    if (!result)
381        result = ERR_PTR(-ESTALE);
382    if (IS_ERR(result))
383        return result;
384
385    if (S_ISDIR(result->d_inode->i_mode)) {
386        /*
387         * This request is for a directory.
388         *
389         * On the positive side there is only one dentry for each
390         * directory inode. On the negative side this implies that we
391         * to ensure our dentry is connected all the way up to the
392         * filesystem root.
393         */
394        if (result->d_flags & DCACHE_DISCONNECTED) {
395            err = reconnect_path(mnt, result, nbuf);
396            if (err)
397                goto err_result;
398        }
399
400        if (!acceptable(context, result)) {
401            err = -EACCES;
402            goto err_result;
403        }
404
405        return result;
406    } else {
407        /*
408         * It's not a directory. Life is a little more complicated.
409         */
410        struct dentry *target_dir, *nresult;
411
412        /*
413         * See if either the dentry we just got from the filesystem
414         * or any alias for it is acceptable. This is always true
415         * if this filesystem is exported without the subtreecheck
416         * option. If the filesystem is exported with the subtree
417         * check option there's a fair chance we need to look at
418         * the parent directory in the file handle and make sure
419         * it's connected to the filesystem root.
420         */
421        alias = find_acceptable_alias(result, acceptable, context);
422        if (alias)
423            return alias;
424
425        /*
426         * Try to extract a dentry for the parent directory from the
427         * file handle. If this fails we'll have to give up.
428         */
429        err = -ESTALE;
430        if (!nop->fh_to_parent)
431            goto err_result;
432
433        target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
434                fh_len, fileid_type);
435        if (!target_dir)
436            goto err_result;
437        err = PTR_ERR(target_dir);
438        if (IS_ERR(target_dir))
439            goto err_result;
440
441        /*
442         * And as usual we need to make sure the parent directory is
443         * connected to the filesystem root. The VFS really doesn't
444         * like disconnected directories..
445         */
446        err = reconnect_path(mnt, target_dir, nbuf);
447        if (err) {
448            dput(target_dir);
449            goto err_result;
450        }
451
452        /*
453         * Now that we've got both a well-connected parent and a
454         * dentry for the inode we're after, make sure that our
455         * inode is actually connected to the parent.
456         */
457        err = exportfs_get_name(mnt, target_dir, nbuf, result);
458        if (!err) {
459            mutex_lock(&target_dir->d_inode->i_mutex);
460            nresult = lookup_one_len(nbuf, target_dir,
461                         strlen(nbuf));
462            mutex_unlock(&target_dir->d_inode->i_mutex);
463            if (!IS_ERR(nresult)) {
464                if (nresult->d_inode) {
465                    dput(result);
466                    result = nresult;
467                } else
468                    dput(nresult);
469            }
470        }
471
472        /*
473         * At this point we are done with the parent, but it's pinned
474         * by the child dentry anyway.
475         */
476        dput(target_dir);
477
478        /*
479         * And finally make sure the dentry is actually acceptable
480         * to NFSD.
481         */
482        alias = find_acceptable_alias(result, acceptable, context);
483        if (!alias) {
484            err = -EACCES;
485            goto err_result;
486        }
487
488        return alias;
489    }
490
491 err_result:
492    dput(result);
493    return ERR_PTR(err);
494}
495EXPORT_SYMBOL_GPL(exportfs_decode_fh);
496
497MODULE_LICENSE("GPL");
498

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