Root/fs/namei.c

1/*
2 * linux/fs/namei.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7/*
8 * Some corrections by tytso.
9 */
10
11/* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
12 * lookup logic.
13 */
14/* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
15 */
16
17#include <linux/init.h>
18#include <linux/module.h>
19#include <linux/slab.h>
20#include <linux/fs.h>
21#include <linux/namei.h>
22#include <linux/pagemap.h>
23#include <linux/fsnotify.h>
24#include <linux/personality.h>
25#include <linux/security.h>
26#include <linux/ima.h>
27#include <linux/syscalls.h>
28#include <linux/mount.h>
29#include <linux/audit.h>
30#include <linux/capability.h>
31#include <linux/file.h>
32#include <linux/fcntl.h>
33#include <linux/device_cgroup.h>
34#include <linux/fs_struct.h>
35#include <asm/uaccess.h>
36
37#include "internal.h"
38
39/* [Feb-1997 T. Schoebel-Theuer]
40 * Fundamental changes in the pathname lookup mechanisms (namei)
41 * were necessary because of omirr. The reason is that omirr needs
42 * to know the _real_ pathname, not the user-supplied one, in case
43 * of symlinks (and also when transname replacements occur).
44 *
45 * The new code replaces the old recursive symlink resolution with
46 * an iterative one (in case of non-nested symlink chains). It does
47 * this with calls to <fs>_follow_link().
48 * As a side effect, dir_namei(), _namei() and follow_link() are now
49 * replaced with a single function lookup_dentry() that can handle all
50 * the special cases of the former code.
51 *
52 * With the new dcache, the pathname is stored at each inode, at least as
53 * long as the refcount of the inode is positive. As a side effect, the
54 * size of the dcache depends on the inode cache and thus is dynamic.
55 *
56 * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
57 * resolution to correspond with current state of the code.
58 *
59 * Note that the symlink resolution is not *completely* iterative.
60 * There is still a significant amount of tail- and mid- recursion in
61 * the algorithm. Also, note that <fs>_readlink() is not used in
62 * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
63 * may return different results than <fs>_follow_link(). Many virtual
64 * filesystems (including /proc) exhibit this behavior.
65 */
66
67/* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
68 * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
69 * and the name already exists in form of a symlink, try to create the new
70 * name indicated by the symlink. The old code always complained that the
71 * name already exists, due to not following the symlink even if its target
72 * is nonexistent. The new semantics affects also mknod() and link() when
73 * the name is a symlink pointing to a non-existent name.
74 *
75 * I don't know which semantics is the right one, since I have no access
76 * to standards. But I found by trial that HP-UX 9.0 has the full "new"
77 * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
78 * "old" one. Personally, I think the new semantics is much more logical.
79 * Note that "ln old new" where "new" is a symlink pointing to a non-existing
80 * file does succeed in both HP-UX and SunOs, but not in Solaris
81 * and in the old Linux semantics.
82 */
83
84/* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
85 * semantics. See the comments in "open_namei" and "do_link" below.
86 *
87 * [10-Sep-98 Alan Modra] Another symlink change.
88 */
89
90/* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
91 * inside the path - always follow.
92 * in the last component in creation/removal/renaming - never follow.
93 * if LOOKUP_FOLLOW passed - follow.
94 * if the pathname has trailing slashes - follow.
95 * otherwise - don't follow.
96 * (applied in that order).
97 *
98 * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
99 * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
100 * During the 2.4 we need to fix the userland stuff depending on it -
101 * hopefully we will be able to get rid of that wart in 2.5. So far only
102 * XEmacs seems to be relying on it...
103 */
104/*
105 * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
106 * implemented. Let's see if raised priority of ->s_vfs_rename_mutex gives
107 * any extra contention...
108 */
109
110/* In order to reduce some races, while at the same time doing additional
111 * checking and hopefully speeding things up, we copy filenames to the
112 * kernel data space before using them..
113 *
114 * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
115 * PATH_MAX includes the nul terminator --RR.
116 */
117static int do_getname(const char __user *filename, char *page)
118{
119    int retval;
120    unsigned long len = PATH_MAX;
121
122    if (!segment_eq(get_fs(), KERNEL_DS)) {
123        if ((unsigned long) filename >= TASK_SIZE)
124            return -EFAULT;
125        if (TASK_SIZE - (unsigned long) filename < PATH_MAX)
126            len = TASK_SIZE - (unsigned long) filename;
127    }
128
129    retval = strncpy_from_user(page, filename, len);
130    if (retval > 0) {
131        if (retval < len)
132            return 0;
133        return -ENAMETOOLONG;
134    } else if (!retval)
135        retval = -ENOENT;
136    return retval;
137}
138
139static char *getname_flags(const char __user * filename, int flags)
140{
141    char *tmp, *result;
142
143    result = ERR_PTR(-ENOMEM);
144    tmp = __getname();
145    if (tmp) {
146        int retval = do_getname(filename, tmp);
147
148        result = tmp;
149        if (retval < 0) {
150            if (retval != -ENOENT || !(flags & LOOKUP_EMPTY)) {
151                __putname(tmp);
152                result = ERR_PTR(retval);
153            }
154        }
155    }
156    audit_getname(result);
157    return result;
158}
159
160char *getname(const char __user * filename)
161{
162    return getname_flags(filename, 0);
163}
164
165#ifdef CONFIG_AUDITSYSCALL
166void putname(const char *name)
167{
168    if (unlikely(!audit_dummy_context()))
169        audit_putname(name);
170    else
171        __putname(name);
172}
173EXPORT_SYMBOL(putname);
174#endif
175
176/*
177 * This does basic POSIX ACL permission checking
178 */
179static int acl_permission_check(struct inode *inode, int mask, unsigned int flags,
180        int (*check_acl)(struct inode *inode, int mask, unsigned int flags))
181{
182    unsigned int mode = inode->i_mode;
183
184    mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
185
186    if (current_user_ns() != inode_userns(inode))
187        goto other_perms;
188
189    if (current_fsuid() == inode->i_uid)
190        mode >>= 6;
191    else {
192        if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
193            int error = check_acl(inode, mask, flags);
194            if (error != -EAGAIN)
195                return error;
196        }
197
198        if (in_group_p(inode->i_gid))
199            mode >>= 3;
200    }
201
202other_perms:
203    /*
204     * If the DACs are ok we don't need any capability check.
205     */
206    if ((mask & ~mode) == 0)
207        return 0;
208    return -EACCES;
209}
210
211/**
212 * generic_permission - check for access rights on a Posix-like filesystem
213 * @inode: inode to check access rights for
214 * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
215 * @check_acl: optional callback to check for Posix ACLs
216 * @flags: IPERM_FLAG_ flags.
217 *
218 * Used to check for read/write/execute permissions on a file.
219 * We use "fsuid" for this, letting us set arbitrary permissions
220 * for filesystem access without changing the "normal" uids which
221 * are used for other things.
222 *
223 * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
224 * request cannot be satisfied (eg. requires blocking or too much complexity).
225 * It would then be called again in ref-walk mode.
226 */
227int generic_permission(struct inode *inode, int mask, unsigned int flags,
228    int (*check_acl)(struct inode *inode, int mask, unsigned int flags))
229{
230    int ret;
231
232    /*
233     * Do the basic POSIX ACL permission checks.
234     */
235    ret = acl_permission_check(inode, mask, flags, check_acl);
236    if (ret != -EACCES)
237        return ret;
238
239    /*
240     * Read/write DACs are always overridable.
241     * Executable DACs are overridable for all directories and
242     * for non-directories that have least one exec bit set.
243     */
244    if (!(mask & MAY_EXEC) || execute_ok(inode))
245        if (ns_capable(inode_userns(inode), CAP_DAC_OVERRIDE))
246            return 0;
247
248    /*
249     * Searching includes executable on directories, else just read.
250     */
251    mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
252    if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
253        if (ns_capable(inode_userns(inode), CAP_DAC_READ_SEARCH))
254            return 0;
255
256    return -EACCES;
257}
258
259/**
260 * inode_permission - check for access rights to a given inode
261 * @inode: inode to check permission on
262 * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
263 *
264 * Used to check for read/write/execute permissions on an inode.
265 * We use "fsuid" for this, letting us set arbitrary permissions
266 * for filesystem access without changing the "normal" uids which
267 * are used for other things.
268 */
269int inode_permission(struct inode *inode, int mask)
270{
271    int retval;
272
273    if (mask & MAY_WRITE) {
274        umode_t mode = inode->i_mode;
275
276        /*
277         * Nobody gets write access to a read-only fs.
278         */
279        if (IS_RDONLY(inode) &&
280            (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
281            return -EROFS;
282
283        /*
284         * Nobody gets write access to an immutable file.
285         */
286        if (IS_IMMUTABLE(inode))
287            return -EACCES;
288    }
289
290    if (inode->i_op->permission)
291        retval = inode->i_op->permission(inode, mask, 0);
292    else
293        retval = generic_permission(inode, mask, 0,
294                inode->i_op->check_acl);
295
296    if (retval)
297        return retval;
298
299    retval = devcgroup_inode_permission(inode, mask);
300    if (retval)
301        return retval;
302
303    return security_inode_permission(inode, mask);
304}
305
306/**
307 * file_permission - check for additional access rights to a given file
308 * @file: file to check access rights for
309 * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
310 *
311 * Used to check for read/write/execute permissions on an already opened
312 * file.
313 *
314 * Note:
315 * Do not use this function in new code. All access checks should
316 * be done using inode_permission().
317 */
318int file_permission(struct file *file, int mask)
319{
320    return inode_permission(file->f_path.dentry->d_inode, mask);
321}
322
323/*
324 * get_write_access() gets write permission for a file.
325 * put_write_access() releases this write permission.
326 * This is used for regular files.
327 * We cannot support write (and maybe mmap read-write shared) accesses and
328 * MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
329 * can have the following values:
330 * 0: no writers, no VM_DENYWRITE mappings
331 * < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
332 * > 0: (i_writecount) users are writing to the file.
333 *
334 * Normally we operate on that counter with atomic_{inc,dec} and it's safe
335 * except for the cases where we don't hold i_writecount yet. Then we need to
336 * use {get,deny}_write_access() - these functions check the sign and refuse
337 * to do the change if sign is wrong. Exclusion between them is provided by
338 * the inode->i_lock spinlock.
339 */
340
341int get_write_access(struct inode * inode)
342{
343    spin_lock(&inode->i_lock);
344    if (atomic_read(&inode->i_writecount) < 0) {
345        spin_unlock(&inode->i_lock);
346        return -ETXTBSY;
347    }
348    atomic_inc(&inode->i_writecount);
349    spin_unlock(&inode->i_lock);
350
351    return 0;
352}
353
354int deny_write_access(struct file * file)
355{
356    struct inode *inode = file->f_path.dentry->d_inode;
357
358    spin_lock(&inode->i_lock);
359    if (atomic_read(&inode->i_writecount) > 0) {
360        spin_unlock(&inode->i_lock);
361        return -ETXTBSY;
362    }
363    atomic_dec(&inode->i_writecount);
364    spin_unlock(&inode->i_lock);
365
366    return 0;
367}
368
369/**
370 * path_get - get a reference to a path
371 * @path: path to get the reference to
372 *
373 * Given a path increment the reference count to the dentry and the vfsmount.
374 */
375void path_get(struct path *path)
376{
377    mntget(path->mnt);
378    dget(path->dentry);
379}
380EXPORT_SYMBOL(path_get);
381
382/**
383 * path_put - put a reference to a path
384 * @path: path to put the reference to
385 *
386 * Given a path decrement the reference count to the dentry and the vfsmount.
387 */
388void path_put(struct path *path)
389{
390    dput(path->dentry);
391    mntput(path->mnt);
392}
393EXPORT_SYMBOL(path_put);
394
395/*
396 * Path walking has 2 modes, rcu-walk and ref-walk (see
397 * Documentation/filesystems/path-lookup.txt). In situations when we can't
398 * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
399 * normal reference counts on dentries and vfsmounts to transition to rcu-walk
400 * mode. Refcounts are grabbed at the last known good point before rcu-walk
401 * got stuck, so ref-walk may continue from there. If this is not successful
402 * (eg. a seqcount has changed), then failure is returned and it's up to caller
403 * to restart the path walk from the beginning in ref-walk mode.
404 */
405
406/**
407 * unlazy_walk - try to switch to ref-walk mode.
408 * @nd: nameidata pathwalk data
409 * @dentry: child of nd->path.dentry or NULL
410 * Returns: 0 on success, -ECHILD on failure
411 *
412 * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
413 * for ref-walk mode. @dentry must be a path found by a do_lookup call on
414 * @nd or NULL. Must be called from rcu-walk context.
415 */
416static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
417{
418    struct fs_struct *fs = current->fs;
419    struct dentry *parent = nd->path.dentry;
420    int want_root = 0;
421
422    BUG_ON(!(nd->flags & LOOKUP_RCU));
423    if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
424        want_root = 1;
425        spin_lock(&fs->lock);
426        if (nd->root.mnt != fs->root.mnt ||
427                nd->root.dentry != fs->root.dentry)
428            goto err_root;
429    }
430    spin_lock(&parent->d_lock);
431    if (!dentry) {
432        if (!__d_rcu_to_refcount(parent, nd->seq))
433            goto err_parent;
434        BUG_ON(nd->inode != parent->d_inode);
435    } else {
436        if (dentry->d_parent != parent)
437            goto err_parent;
438        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
439        if (!__d_rcu_to_refcount(dentry, nd->seq))
440            goto err_child;
441        /*
442         * If the sequence check on the child dentry passed, then
443         * the child has not been removed from its parent. This
444         * means the parent dentry must be valid and able to take
445         * a reference at this point.
446         */
447        BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
448        BUG_ON(!parent->d_count);
449        parent->d_count++;
450        spin_unlock(&dentry->d_lock);
451    }
452    spin_unlock(&parent->d_lock);
453    if (want_root) {
454        path_get(&nd->root);
455        spin_unlock(&fs->lock);
456    }
457    mntget(nd->path.mnt);
458
459    rcu_read_unlock();
460    br_read_unlock(vfsmount_lock);
461    nd->flags &= ~LOOKUP_RCU;
462    return 0;
463
464err_child:
465    spin_unlock(&dentry->d_lock);
466err_parent:
467    spin_unlock(&parent->d_lock);
468err_root:
469    if (want_root)
470        spin_unlock(&fs->lock);
471    return -ECHILD;
472}
473
474/**
475 * release_open_intent - free up open intent resources
476 * @nd: pointer to nameidata
477 */
478void release_open_intent(struct nameidata *nd)
479{
480    struct file *file = nd->intent.open.file;
481
482    if (file && !IS_ERR(file)) {
483        if (file->f_path.dentry == NULL)
484            put_filp(file);
485        else
486            fput(file);
487    }
488}
489
490static inline int d_revalidate(struct dentry *dentry, struct nameidata *nd)
491{
492    return dentry->d_op->d_revalidate(dentry, nd);
493}
494
495static struct dentry *
496do_revalidate(struct dentry *dentry, struct nameidata *nd)
497{
498    int status = d_revalidate(dentry, nd);
499    if (unlikely(status <= 0)) {
500        /*
501         * The dentry failed validation.
502         * If d_revalidate returned 0 attempt to invalidate
503         * the dentry otherwise d_revalidate is asking us
504         * to return a fail status.
505         */
506        if (status < 0) {
507            dput(dentry);
508            dentry = ERR_PTR(status);
509        } else if (!d_invalidate(dentry)) {
510            dput(dentry);
511            dentry = NULL;
512        }
513    }
514    return dentry;
515}
516
517/**
518 * complete_walk - successful completion of path walk
519 * @nd: pointer nameidata
520 *
521 * If we had been in RCU mode, drop out of it and legitimize nd->path.
522 * Revalidate the final result, unless we'd already done that during
523 * the path walk or the filesystem doesn't ask for it. Return 0 on
524 * success, -error on failure. In case of failure caller does not
525 * need to drop nd->path.
526 */
527static int complete_walk(struct nameidata *nd)
528{
529    struct dentry *dentry = nd->path.dentry;
530    int status;
531
532    if (nd->flags & LOOKUP_RCU) {
533        nd->flags &= ~LOOKUP_RCU;
534        if (!(nd->flags & LOOKUP_ROOT))
535            nd->root.mnt = NULL;
536        spin_lock(&dentry->d_lock);
537        if (unlikely(!__d_rcu_to_refcount(dentry, nd->seq))) {
538            spin_unlock(&dentry->d_lock);
539            rcu_read_unlock();
540            br_read_unlock(vfsmount_lock);
541            return -ECHILD;
542        }
543        BUG_ON(nd->inode != dentry->d_inode);
544        spin_unlock(&dentry->d_lock);
545        mntget(nd->path.mnt);
546        rcu_read_unlock();
547        br_read_unlock(vfsmount_lock);
548    }
549
550    if (likely(!(nd->flags & LOOKUP_JUMPED)))
551        return 0;
552
553    if (likely(!(dentry->d_flags & DCACHE_OP_REVALIDATE)))
554        return 0;
555
556    if (likely(!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)))
557        return 0;
558
559    /* Note: we do not d_invalidate() */
560    status = d_revalidate(dentry, nd);
561    if (status > 0)
562        return 0;
563
564    if (!status)
565        status = -ESTALE;
566
567    path_put(&nd->path);
568    return status;
569}
570
571/*
572 * Short-cut version of permission(), for calling on directories
573 * during pathname resolution. Combines parts of permission()
574 * and generic_permission(), and tests ONLY for MAY_EXEC permission.
575 *
576 * If appropriate, check DAC only. If not appropriate, or
577 * short-cut DAC fails, then call ->permission() to do more
578 * complete permission check.
579 */
580static inline int exec_permission(struct inode *inode, unsigned int flags)
581{
582    int ret;
583    struct user_namespace *ns = inode_userns(inode);
584
585    if (inode->i_op->permission) {
586        ret = inode->i_op->permission(inode, MAY_EXEC, flags);
587    } else {
588        ret = acl_permission_check(inode, MAY_EXEC, flags,
589                inode->i_op->check_acl);
590    }
591    if (likely(!ret))
592        goto ok;
593    if (ret == -ECHILD)
594        return ret;
595
596    if (ns_capable(ns, CAP_DAC_OVERRIDE) ||
597            ns_capable(ns, CAP_DAC_READ_SEARCH))
598        goto ok;
599
600    return ret;
601ok:
602    return security_inode_exec_permission(inode, flags);
603}
604
605static __always_inline void set_root(struct nameidata *nd)
606{
607    if (!nd->root.mnt)
608        get_fs_root(current->fs, &nd->root);
609}
610
611static int link_path_walk(const char *, struct nameidata *);
612
613static __always_inline void set_root_rcu(struct nameidata *nd)
614{
615    if (!nd->root.mnt) {
616        struct fs_struct *fs = current->fs;
617        unsigned seq;
618
619        do {
620            seq = read_seqcount_begin(&fs->seq);
621            nd->root = fs->root;
622            nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
623        } while (read_seqcount_retry(&fs->seq, seq));
624    }
625}
626
627static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link)
628{
629    int ret;
630
631    if (IS_ERR(link))
632        goto fail;
633
634    if (*link == '/') {
635        set_root(nd);
636        path_put(&nd->path);
637        nd->path = nd->root;
638        path_get(&nd->root);
639        nd->flags |= LOOKUP_JUMPED;
640    }
641    nd->inode = nd->path.dentry->d_inode;
642
643    ret = link_path_walk(link, nd);
644    return ret;
645fail:
646    path_put(&nd->path);
647    return PTR_ERR(link);
648}
649
650static void path_put_conditional(struct path *path, struct nameidata *nd)
651{
652    dput(path->dentry);
653    if (path->mnt != nd->path.mnt)
654        mntput(path->mnt);
655}
656
657static inline void path_to_nameidata(const struct path *path,
658                    struct nameidata *nd)
659{
660    if (!(nd->flags & LOOKUP_RCU)) {
661        dput(nd->path.dentry);
662        if (nd->path.mnt != path->mnt)
663            mntput(nd->path.mnt);
664    }
665    nd->path.mnt = path->mnt;
666    nd->path.dentry = path->dentry;
667}
668
669static inline void put_link(struct nameidata *nd, struct path *link, void *cookie)
670{
671    struct inode *inode = link->dentry->d_inode;
672    if (!IS_ERR(cookie) && inode->i_op->put_link)
673        inode->i_op->put_link(link->dentry, nd, cookie);
674    path_put(link);
675}
676
677static __always_inline int
678follow_link(struct path *link, struct nameidata *nd, void **p)
679{
680    int error;
681    struct dentry *dentry = link->dentry;
682
683    BUG_ON(nd->flags & LOOKUP_RCU);
684
685    if (link->mnt == nd->path.mnt)
686        mntget(link->mnt);
687
688    if (unlikely(current->total_link_count >= 40)) {
689        *p = ERR_PTR(-ELOOP); /* no ->put_link(), please */
690        path_put(&nd->path);
691        return -ELOOP;
692    }
693    cond_resched();
694    current->total_link_count++;
695
696    touch_atime(link->mnt, dentry);
697    nd_set_link(nd, NULL);
698
699    error = security_inode_follow_link(link->dentry, nd);
700    if (error) {
701        *p = ERR_PTR(error); /* no ->put_link(), please */
702        path_put(&nd->path);
703        return error;
704    }
705
706    nd->last_type = LAST_BIND;
707    *p = dentry->d_inode->i_op->follow_link(dentry, nd);
708    error = PTR_ERR(*p);
709    if (!IS_ERR(*p)) {
710        char *s = nd_get_link(nd);
711        error = 0;
712        if (s)
713            error = __vfs_follow_link(nd, s);
714        else if (nd->last_type == LAST_BIND) {
715            nd->flags |= LOOKUP_JUMPED;
716            nd->inode = nd->path.dentry->d_inode;
717            if (nd->inode->i_op->follow_link) {
718                /* stepped on a _really_ weird one */
719                path_put(&nd->path);
720                error = -ELOOP;
721            }
722        }
723    }
724    return error;
725}
726
727static int follow_up_rcu(struct path *path)
728{
729    struct vfsmount *parent;
730    struct dentry *mountpoint;
731
732    parent = path->mnt->mnt_parent;
733    if (parent == path->mnt)
734        return 0;
735    mountpoint = path->mnt->mnt_mountpoint;
736    path->dentry = mountpoint;
737    path->mnt = parent;
738    return 1;
739}
740
741int follow_up(struct path *path)
742{
743    struct vfsmount *parent;
744    struct dentry *mountpoint;
745
746    br_read_lock(vfsmount_lock);
747    parent = path->mnt->mnt_parent;
748    if (parent == path->mnt) {
749        br_read_unlock(vfsmount_lock);
750        return 0;
751    }
752    mntget(parent);
753    mountpoint = dget(path->mnt->mnt_mountpoint);
754    br_read_unlock(vfsmount_lock);
755    dput(path->dentry);
756    path->dentry = mountpoint;
757    mntput(path->mnt);
758    path->mnt = parent;
759    return 1;
760}
761
762/*
763 * Perform an automount
764 * - return -EISDIR to tell follow_managed() to stop and return the path we
765 * were called with.
766 */
767static int follow_automount(struct path *path, unsigned flags,
768                bool *need_mntput)
769{
770    struct vfsmount *mnt;
771    int err;
772
773    if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
774        return -EREMOTE;
775
776    /* We don't want to mount if someone supplied AT_NO_AUTOMOUNT
777     * and this is the terminal part of the path.
778     */
779    if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
780        return -EISDIR; /* we actually want to stop here */
781
782    /* We want to mount if someone is trying to open/create a file of any
783     * type under the mountpoint, wants to traverse through the mountpoint
784     * or wants to open the mounted directory.
785     *
786     * We don't want to mount if someone's just doing a stat and they've
787     * set AT_SYMLINK_NOFOLLOW - unless they're stat'ing a directory and
788     * appended a '/' to the name.
789     */
790    if (!(flags & LOOKUP_FOLLOW) &&
791        !(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY |
792               LOOKUP_OPEN | LOOKUP_CREATE)))
793        return -EISDIR;
794
795    current->total_link_count++;
796    if (current->total_link_count >= 40)
797        return -ELOOP;
798
799    mnt = path->dentry->d_op->d_automount(path);
800    if (IS_ERR(mnt)) {
801        /*
802         * The filesystem is allowed to return -EISDIR here to indicate
803         * it doesn't want to automount. For instance, autofs would do
804         * this so that its userspace daemon can mount on this dentry.
805         *
806         * However, we can only permit this if it's a terminal point in
807         * the path being looked up; if it wasn't then the remainder of
808         * the path is inaccessible and we should say so.
809         */
810        if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_CONTINUE))
811            return -EREMOTE;
812        return PTR_ERR(mnt);
813    }
814
815    if (!mnt) /* mount collision */
816        return 0;
817
818    if (!*need_mntput) {
819        /* lock_mount() may release path->mnt on error */
820        mntget(path->mnt);
821        *need_mntput = true;
822    }
823    err = finish_automount(mnt, path);
824
825    switch (err) {
826    case -EBUSY:
827        /* Someone else made a mount here whilst we were busy */
828        return 0;
829    case 0:
830        path_put(path);
831        path->mnt = mnt;
832        path->dentry = dget(mnt->mnt_root);
833        return 0;
834    default:
835        return err;
836    }
837
838}
839
840/*
841 * Handle a dentry that is managed in some way.
842 * - Flagged for transit management (autofs)
843 * - Flagged as mountpoint
844 * - Flagged as automount point
845 *
846 * This may only be called in refwalk mode.
847 *
848 * Serialization is taken care of in namespace.c
849 */
850static int follow_managed(struct path *path, unsigned flags)
851{
852    struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
853    unsigned managed;
854    bool need_mntput = false;
855    int ret = 0;
856
857    /* Given that we're not holding a lock here, we retain the value in a
858     * local variable for each dentry as we look at it so that we don't see
859     * the components of that value change under us */
860    while (managed = ACCESS_ONCE(path->dentry->d_flags),
861           managed &= DCACHE_MANAGED_DENTRY,
862           unlikely(managed != 0)) {
863        /* Allow the filesystem to manage the transit without i_mutex
864         * being held. */
865        if (managed & DCACHE_MANAGE_TRANSIT) {
866            BUG_ON(!path->dentry->d_op);
867            BUG_ON(!path->dentry->d_op->d_manage);
868            ret = path->dentry->d_op->d_manage(path->dentry, false);
869            if (ret < 0)
870                break;
871        }
872
873        /* Transit to a mounted filesystem. */
874        if (managed & DCACHE_MOUNTED) {
875            struct vfsmount *mounted = lookup_mnt(path);
876            if (mounted) {
877                dput(path->dentry);
878                if (need_mntput)
879                    mntput(path->mnt);
880                path->mnt = mounted;
881                path->dentry = dget(mounted->mnt_root);
882                need_mntput = true;
883                continue;
884            }
885
886            /* Something is mounted on this dentry in another
887             * namespace and/or whatever was mounted there in this
888             * namespace got unmounted before we managed to get the
889             * vfsmount_lock */
890        }
891
892        /* Handle an automount point */
893        if (managed & DCACHE_NEED_AUTOMOUNT) {
894            ret = follow_automount(path, flags, &need_mntput);
895            if (ret < 0)
896                break;
897            continue;
898        }
899
900        /* We didn't change the current path point */
901        break;
902    }
903
904    if (need_mntput && path->mnt == mnt)
905        mntput(path->mnt);
906    if (ret == -EISDIR)
907        ret = 0;
908    return ret;
909}
910
911int follow_down_one(struct path *path)
912{
913    struct vfsmount *mounted;
914
915    mounted = lookup_mnt(path);
916    if (mounted) {
917        dput(path->dentry);
918        mntput(path->mnt);
919        path->mnt = mounted;
920        path->dentry = dget(mounted->mnt_root);
921        return 1;
922    }
923    return 0;
924}
925
926static inline bool managed_dentry_might_block(struct dentry *dentry)
927{
928    return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
929        dentry->d_op->d_manage(dentry, true) < 0);
930}
931
932/*
933 * Try to skip to top of mountpoint pile in rcuwalk mode. Fail if
934 * we meet a managed dentry that would need blocking.
935 */
936static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
937                   struct inode **inode)
938{
939    for (;;) {
940        struct vfsmount *mounted;
941        /*
942         * Don't forget we might have a non-mountpoint managed dentry
943         * that wants to block transit.
944         */
945        if (unlikely(managed_dentry_might_block(path->dentry)))
946            return false;
947
948        if (!d_mountpoint(path->dentry))
949            break;
950
951        mounted = __lookup_mnt(path->mnt, path->dentry, 1);
952        if (!mounted)
953            break;
954        path->mnt = mounted;
955        path->dentry = mounted->mnt_root;
956        nd->seq = read_seqcount_begin(&path->dentry->d_seq);
957        /*
958         * Update the inode too. We don't need to re-check the
959         * dentry sequence number here after this d_inode read,
960         * because a mount-point is always pinned.
961         */
962        *inode = path->dentry->d_inode;
963    }
964    return true;
965}
966
967static void follow_mount_rcu(struct nameidata *nd)
968{
969    while (d_mountpoint(nd->path.dentry)) {
970        struct vfsmount *mounted;
971        mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry, 1);
972        if (!mounted)
973            break;
974        nd->path.mnt = mounted;
975        nd->path.dentry = mounted->mnt_root;
976        nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
977    }
978}
979
980static int follow_dotdot_rcu(struct nameidata *nd)
981{
982    set_root_rcu(nd);
983
984    while (1) {
985        if (nd->path.dentry == nd->root.dentry &&
986            nd->path.mnt == nd->root.mnt) {
987            break;
988        }
989        if (nd->path.dentry != nd->path.mnt->mnt_root) {
990            struct dentry *old = nd->path.dentry;
991            struct dentry *parent = old->d_parent;
992            unsigned seq;
993
994            seq = read_seqcount_begin(&parent->d_seq);
995            if (read_seqcount_retry(&old->d_seq, nd->seq))
996                goto failed;
997            nd->path.dentry = parent;
998            nd->seq = seq;
999            break;
1000        }
1001        if (!follow_up_rcu(&nd->path))
1002            break;
1003        nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
1004    }
1005    follow_mount_rcu(nd);
1006    nd->inode = nd->path.dentry->d_inode;
1007    return 0;
1008
1009failed:
1010    nd->flags &= ~LOOKUP_RCU;
1011    if (!(nd->flags & LOOKUP_ROOT))
1012        nd->root.mnt = NULL;
1013    rcu_read_unlock();
1014    br_read_unlock(vfsmount_lock);
1015    return -ECHILD;
1016}
1017
1018/*
1019 * Follow down to the covering mount currently visible to userspace. At each
1020 * point, the filesystem owning that dentry may be queried as to whether the
1021 * caller is permitted to proceed or not.
1022 */
1023int follow_down(struct path *path)
1024{
1025    unsigned managed;
1026    int ret;
1027
1028    while (managed = ACCESS_ONCE(path->dentry->d_flags),
1029           unlikely(managed & DCACHE_MANAGED_DENTRY)) {
1030        /* Allow the filesystem to manage the transit without i_mutex
1031         * being held.
1032         *
1033         * We indicate to the filesystem if someone is trying to mount
1034         * something here. This gives autofs the chance to deny anyone
1035         * other than its daemon the right to mount on its
1036         * superstructure.
1037         *
1038         * The filesystem may sleep at this point.
1039         */
1040        if (managed & DCACHE_MANAGE_TRANSIT) {
1041            BUG_ON(!path->dentry->d_op);
1042            BUG_ON(!path->dentry->d_op->d_manage);
1043            ret = path->dentry->d_op->d_manage(
1044                path->dentry, false);
1045            if (ret < 0)
1046                return ret == -EISDIR ? 0 : ret;
1047        }
1048
1049        /* Transit to a mounted filesystem. */
1050        if (managed & DCACHE_MOUNTED) {
1051            struct vfsmount *mounted = lookup_mnt(path);
1052            if (!mounted)
1053                break;
1054            dput(path->dentry);
1055            mntput(path->mnt);
1056            path->mnt = mounted;
1057            path->dentry = dget(mounted->mnt_root);
1058            continue;
1059        }
1060
1061        /* Don't handle automount points here */
1062        break;
1063    }
1064    return 0;
1065}
1066
1067/*
1068 * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
1069 */
1070static void follow_mount(struct path *path)
1071{
1072    while (d_mountpoint(path->dentry)) {
1073        struct vfsmount *mounted = lookup_mnt(path);
1074        if (!mounted)
1075            break;
1076        dput(path->dentry);
1077        mntput(path->mnt);
1078        path->mnt = mounted;
1079        path->dentry = dget(mounted->mnt_root);
1080    }
1081}
1082
1083static void follow_dotdot(struct nameidata *nd)
1084{
1085    set_root(nd);
1086
1087    while(1) {
1088        struct dentry *old = nd->path.dentry;
1089
1090        if (nd->path.dentry == nd->root.dentry &&
1091            nd->path.mnt == nd->root.mnt) {
1092            break;
1093        }
1094        if (nd->path.dentry != nd->path.mnt->mnt_root) {
1095            /* rare case of legitimate dget_parent()... */
1096            nd->path.dentry = dget_parent(nd->path.dentry);
1097            dput(old);
1098            break;
1099        }
1100        if (!follow_up(&nd->path))
1101            break;
1102    }
1103    follow_mount(&nd->path);
1104    nd->inode = nd->path.dentry->d_inode;
1105}
1106
1107/*
1108 * Allocate a dentry with name and parent, and perform a parent
1109 * directory ->lookup on it. Returns the new dentry, or ERR_PTR
1110 * on error. parent->d_inode->i_mutex must be held. d_lookup must
1111 * have verified that no child exists while under i_mutex.
1112 */
1113static struct dentry *d_alloc_and_lookup(struct dentry *parent,
1114                struct qstr *name, struct nameidata *nd)
1115{
1116    struct inode *inode = parent->d_inode;
1117    struct dentry *dentry;
1118    struct dentry *old;
1119
1120    /* Don't create child dentry for a dead directory. */
1121    if (unlikely(IS_DEADDIR(inode)))
1122        return ERR_PTR(-ENOENT);
1123
1124    dentry = d_alloc(parent, name);
1125    if (unlikely(!dentry))
1126        return ERR_PTR(-ENOMEM);
1127
1128    old = inode->i_op->lookup(inode, dentry, nd);
1129    if (unlikely(old)) {
1130        dput(dentry);
1131        dentry = old;
1132    }
1133    return dentry;
1134}
1135
1136/*
1137 * It's more convoluted than I'd like it to be, but... it's still fairly
1138 * small and for now I'd prefer to have fast path as straight as possible.
1139 * It _is_ time-critical.
1140 */
1141static int do_lookup(struct nameidata *nd, struct qstr *name,
1142            struct path *path, struct inode **inode)
1143{
1144    struct vfsmount *mnt = nd->path.mnt;
1145    struct dentry *dentry, *parent = nd->path.dentry;
1146    int need_reval = 1;
1147    int status = 1;
1148    int err;
1149
1150    /*
1151     * Rename seqlock is not required here because in the off chance
1152     * of a false negative due to a concurrent rename, we're going to
1153     * do the non-racy lookup, below.
1154     */
1155    if (nd->flags & LOOKUP_RCU) {
1156        unsigned seq;
1157        *inode = nd->inode;
1158        dentry = __d_lookup_rcu(parent, name, &seq, inode);
1159        if (!dentry)
1160            goto unlazy;
1161
1162        /* Memory barrier in read_seqcount_begin of child is enough */
1163        if (__read_seqcount_retry(&parent->d_seq, nd->seq))
1164            return -ECHILD;
1165        nd->seq = seq;
1166
1167        if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
1168            status = d_revalidate(dentry, nd);
1169            if (unlikely(status <= 0)) {
1170                if (status != -ECHILD)
1171                    need_reval = 0;
1172                goto unlazy;
1173            }
1174        }
1175        path->mnt = mnt;
1176        path->dentry = dentry;
1177        if (unlikely(!__follow_mount_rcu(nd, path, inode)))
1178            goto unlazy;
1179        if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
1180            goto unlazy;
1181        return 0;
1182unlazy:
1183        if (unlazy_walk(nd, dentry))
1184            return -ECHILD;
1185    } else {
1186        dentry = __d_lookup(parent, name);
1187    }
1188
1189retry:
1190    if (unlikely(!dentry)) {
1191        struct inode *dir = parent->d_inode;
1192        BUG_ON(nd->inode != dir);
1193
1194        mutex_lock(&dir->i_mutex);
1195        dentry = d_lookup(parent, name);
1196        if (likely(!dentry)) {
1197            dentry = d_alloc_and_lookup(parent, name, nd);
1198            if (IS_ERR(dentry)) {
1199                mutex_unlock(&dir->i_mutex);
1200                return PTR_ERR(dentry);
1201            }
1202            /* known good */
1203            need_reval = 0;
1204            status = 1;
1205        }
1206        mutex_unlock(&dir->i_mutex);
1207    }
1208    if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
1209        status = d_revalidate(dentry, nd);
1210    if (unlikely(status <= 0)) {
1211        if (status < 0) {
1212            dput(dentry);
1213            return status;
1214        }
1215        if (!d_invalidate(dentry)) {
1216            dput(dentry);
1217            dentry = NULL;
1218            need_reval = 1;
1219            goto retry;
1220        }
1221    }
1222
1223    path->mnt = mnt;
1224    path->dentry = dentry;
1225    err = follow_managed(path, nd->flags);
1226    if (unlikely(err < 0)) {
1227        path_put_conditional(path, nd);
1228        return err;
1229    }
1230    *inode = path->dentry->d_inode;
1231    return 0;
1232}
1233
1234static inline int may_lookup(struct nameidata *nd)
1235{
1236    if (nd->flags & LOOKUP_RCU) {
1237        int err = exec_permission(nd->inode, IPERM_FLAG_RCU);
1238        if (err != -ECHILD)
1239            return err;
1240        if (unlazy_walk(nd, NULL))
1241            return -ECHILD;
1242    }
1243    return exec_permission(nd->inode, 0);
1244}
1245
1246static inline int handle_dots(struct nameidata *nd, int type)
1247{
1248    if (type == LAST_DOTDOT) {
1249        if (nd->flags & LOOKUP_RCU) {
1250            if (follow_dotdot_rcu(nd))
1251                return -ECHILD;
1252        } else
1253            follow_dotdot(nd);
1254    }
1255    return 0;
1256}
1257
1258static void terminate_walk(struct nameidata *nd)
1259{
1260    if (!(nd->flags & LOOKUP_RCU)) {
1261        path_put(&nd->path);
1262    } else {
1263        nd->flags &= ~LOOKUP_RCU;
1264        if (!(nd->flags & LOOKUP_ROOT))
1265            nd->root.mnt = NULL;
1266        rcu_read_unlock();
1267        br_read_unlock(vfsmount_lock);
1268    }
1269}
1270
1271static inline int walk_component(struct nameidata *nd, struct path *path,
1272        struct qstr *name, int type, int follow)
1273{
1274    struct inode *inode;
1275    int err;
1276    /*
1277     * "." and ".." are special - ".." especially so because it has
1278     * to be able to know about the current root directory and
1279     * parent relationships.
1280     */
1281    if (unlikely(type != LAST_NORM))
1282        return handle_dots(nd, type);
1283    err = do_lookup(nd, name, path, &inode);
1284    if (unlikely(err)) {
1285        terminate_walk(nd);
1286        return err;
1287    }
1288    if (!inode) {
1289        path_to_nameidata(path, nd);
1290        terminate_walk(nd);
1291        return -ENOENT;
1292    }
1293    if (unlikely(inode->i_op->follow_link) && follow) {
1294        if (nd->flags & LOOKUP_RCU) {
1295            if (unlikely(unlazy_walk(nd, path->dentry))) {
1296                terminate_walk(nd);
1297                return -ECHILD;
1298            }
1299        }
1300        BUG_ON(inode != path->dentry->d_inode);
1301        return 1;
1302    }
1303    path_to_nameidata(path, nd);
1304    nd->inode = inode;
1305    return 0;
1306}
1307
1308/*
1309 * This limits recursive symlink follows to 8, while
1310 * limiting consecutive symlinks to 40.
1311 *
1312 * Without that kind of total limit, nasty chains of consecutive
1313 * symlinks can cause almost arbitrarily long lookups.
1314 */
1315static inline int nested_symlink(struct path *path, struct nameidata *nd)
1316{
1317    int res;
1318
1319    if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
1320        path_put_conditional(path, nd);
1321        path_put(&nd->path);
1322        return -ELOOP;
1323    }
1324    BUG_ON(nd->depth >= MAX_NESTED_LINKS);
1325
1326    nd->depth++;
1327    current->link_count++;
1328
1329    do {
1330        struct path link = *path;
1331        void *cookie;
1332
1333        res = follow_link(&link, nd, &cookie);
1334        if (!res)
1335            res = walk_component(nd, path, &nd->last,
1336                         nd->last_type, LOOKUP_FOLLOW);
1337        put_link(nd, &link, cookie);
1338    } while (res > 0);
1339
1340    current->link_count--;
1341    nd->depth--;
1342    return res;
1343}
1344
1345/*
1346 * Name resolution.
1347 * This is the basic name resolution function, turning a pathname into
1348 * the final dentry. We expect 'base' to be positive and a directory.
1349 *
1350 * Returns 0 and nd will have valid dentry and mnt on success.
1351 * Returns error and drops reference to input namei data on failure.
1352 */
1353static int link_path_walk(const char *name, struct nameidata *nd)
1354{
1355    struct path next;
1356    int err;
1357    unsigned int lookup_flags = nd->flags;
1358    
1359    while (*name=='/')
1360        name++;
1361    if (!*name)
1362        return 0;
1363
1364    /* At this point we know we have a real path component. */
1365    for(;;) {
1366        unsigned long hash;
1367        struct qstr this;
1368        unsigned int c;
1369        int type;
1370
1371        nd->flags |= LOOKUP_CONTINUE;
1372
1373        err = may_lookup(nd);
1374         if (err)
1375            break;
1376
1377        this.name = name;
1378        c = *(const unsigned char *)name;
1379
1380        hash = init_name_hash();
1381        do {
1382            name++;
1383            hash = partial_name_hash(c, hash);
1384            c = *(const unsigned char *)name;
1385        } while (c && (c != '/'));
1386        this.len = name - (const char *) this.name;
1387        this.hash = end_name_hash(hash);
1388
1389        type = LAST_NORM;
1390        if (this.name[0] == '.') switch (this.len) {
1391            case 2:
1392                if (this.name[1] == '.') {
1393                    type = LAST_DOTDOT;
1394                    nd->flags |= LOOKUP_JUMPED;
1395                }
1396                break;
1397            case 1:
1398                type = LAST_DOT;
1399        }
1400        if (likely(type == LAST_NORM)) {
1401            struct dentry *parent = nd->path.dentry;
1402            nd->flags &= ~LOOKUP_JUMPED;
1403            if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
1404                err = parent->d_op->d_hash(parent, nd->inode,
1405                               &this);
1406                if (err < 0)
1407                    break;
1408            }
1409        }
1410
1411        /* remove trailing slashes? */
1412        if (!c)
1413            goto last_component;
1414        while (*++name == '/');
1415        if (!*name)
1416            goto last_component;
1417
1418        err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW);
1419        if (err < 0)
1420            return err;
1421
1422        if (err) {
1423            err = nested_symlink(&next, nd);
1424            if (err)
1425                return err;
1426        }
1427        err = -ENOTDIR;
1428        if (!nd->inode->i_op->lookup)
1429            break;
1430        continue;
1431        /* here ends the main loop */
1432
1433last_component:
1434        /* Clear LOOKUP_CONTINUE iff it was previously unset */
1435        nd->flags &= lookup_flags | ~LOOKUP_CONTINUE;
1436        nd->last = this;
1437        nd->last_type = type;
1438        return 0;
1439    }
1440    terminate_walk(nd);
1441    return err;
1442}
1443
1444static int path_init(int dfd, const char *name, unsigned int flags,
1445             struct nameidata *nd, struct file **fp)
1446{
1447    int retval = 0;
1448    int fput_needed;
1449    struct file *file;
1450
1451    nd->last_type = LAST_ROOT; /* if there are only slashes... */
1452    nd->flags = flags | LOOKUP_JUMPED;
1453    nd->depth = 0;
1454    if (flags & LOOKUP_ROOT) {
1455        struct inode *inode = nd->root.dentry->d_inode;
1456        if (*name) {
1457            if (!inode->i_op->lookup)
1458                return -ENOTDIR;
1459            retval = inode_permission(inode, MAY_EXEC);
1460            if (retval)
1461                return retval;
1462        }
1463        nd->path = nd->root;
1464        nd->inode = inode;
1465        if (flags & LOOKUP_RCU) {
1466            br_read_lock(vfsmount_lock);
1467            rcu_read_lock();
1468            nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1469        } else {
1470            path_get(&nd->path);
1471        }
1472        return 0;
1473    }
1474
1475    nd->root.mnt = NULL;
1476
1477    if (*name=='/') {
1478        if (flags & LOOKUP_RCU) {
1479            br_read_lock(vfsmount_lock);
1480            rcu_read_lock();
1481            set_root_rcu(nd);
1482        } else {
1483            set_root(nd);
1484            path_get(&nd->root);
1485        }
1486        nd->path = nd->root;
1487    } else if (dfd == AT_FDCWD) {
1488        if (flags & LOOKUP_RCU) {
1489            struct fs_struct *fs = current->fs;
1490            unsigned seq;
1491
1492            br_read_lock(vfsmount_lock);
1493            rcu_read_lock();
1494
1495            do {
1496                seq = read_seqcount_begin(&fs->seq);
1497                nd->path = fs->pwd;
1498                nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1499            } while (read_seqcount_retry(&fs->seq, seq));
1500        } else {
1501            get_fs_pwd(current->fs, &nd->path);
1502        }
1503    } else {
1504        struct dentry *dentry;
1505
1506        file = fget_raw_light(dfd, &fput_needed);
1507        retval = -EBADF;
1508        if (!file)
1509            goto out_fail;
1510
1511        dentry = file->f_path.dentry;
1512
1513        if (*name) {
1514            retval = -ENOTDIR;
1515            if (!S_ISDIR(dentry->d_inode->i_mode))
1516                goto fput_fail;
1517
1518            retval = file_permission(file, MAY_EXEC);
1519            if (retval)
1520                goto fput_fail;
1521        }
1522
1523        nd->path = file->f_path;
1524        if (flags & LOOKUP_RCU) {
1525            if (fput_needed)
1526                *fp = file;
1527            nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1528            br_read_lock(vfsmount_lock);
1529            rcu_read_lock();
1530        } else {
1531            path_get(&file->f_path);
1532            fput_light(file, fput_needed);
1533        }
1534    }
1535
1536    nd->inode = nd->path.dentry->d_inode;
1537    return 0;
1538
1539fput_fail:
1540    fput_light(file, fput_needed);
1541out_fail:
1542    return retval;
1543}
1544
1545static inline int lookup_last(struct nameidata *nd, struct path *path)
1546{
1547    if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
1548        nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
1549
1550    nd->flags &= ~LOOKUP_PARENT;
1551    return walk_component(nd, path, &nd->last, nd->last_type,
1552                    nd->flags & LOOKUP_FOLLOW);
1553}
1554
1555/* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
1556static int path_lookupat(int dfd, const char *name,
1557                unsigned int flags, struct nameidata *nd)
1558{
1559    struct file *base = NULL;
1560    struct path path;
1561    int err;
1562
1563    /*
1564     * Path walking is largely split up into 2 different synchronisation
1565     * schemes, rcu-walk and ref-walk (explained in
1566     * Documentation/filesystems/path-lookup.txt). These share much of the
1567     * path walk code, but some things particularly setup, cleanup, and
1568     * following mounts are sufficiently divergent that functions are
1569     * duplicated. Typically there is a function foo(), and its RCU
1570     * analogue, foo_rcu().
1571     *
1572     * -ECHILD is the error number of choice (just to avoid clashes) that
1573     * is returned if some aspect of an rcu-walk fails. Such an error must
1574     * be handled by restarting a traditional ref-walk (which will always
1575     * be able to complete).
1576     */
1577    err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base);
1578
1579    if (unlikely(err))
1580        return err;
1581
1582    current->total_link_count = 0;
1583    err = link_path_walk(name, nd);
1584
1585    if (!err && !(flags & LOOKUP_PARENT)) {
1586        err = lookup_last(nd, &path);
1587        while (err > 0) {
1588            void *cookie;
1589            struct path link = path;
1590            nd->flags |= LOOKUP_PARENT;
1591            err = follow_link(&link, nd, &cookie);
1592            if (!err)
1593                err = lookup_last(nd, &path);
1594            put_link(nd, &link, cookie);
1595        }
1596    }
1597
1598    if (!err)
1599        err = complete_walk(nd);
1600
1601    if (!err && nd->flags & LOOKUP_DIRECTORY) {
1602        if (!nd->inode->i_op->lookup) {
1603            path_put(&nd->path);
1604            err = -ENOTDIR;
1605        }
1606    }
1607
1608    if (base)
1609        fput(base);
1610
1611    if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
1612        path_put(&nd->root);
1613        nd->root.mnt = NULL;
1614    }
1615    return err;
1616}
1617
1618static int do_path_lookup(int dfd, const char *name,
1619                unsigned int flags, struct nameidata *nd)
1620{
1621    int retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);
1622    if (unlikely(retval == -ECHILD))
1623        retval = path_lookupat(dfd, name, flags, nd);
1624    if (unlikely(retval == -ESTALE))
1625        retval = path_lookupat(dfd, name, flags | LOOKUP_REVAL, nd);
1626
1627    if (likely(!retval)) {
1628        if (unlikely(!audit_dummy_context())) {
1629            if (nd->path.dentry && nd->inode)
1630                audit_inode(name, nd->path.dentry);
1631        }
1632    }
1633    return retval;
1634}
1635
1636int kern_path_parent(const char *name, struct nameidata *nd)
1637{
1638    return do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, nd);
1639}
1640
1641int kern_path(const char *name, unsigned int flags, struct path *path)
1642{
1643    struct nameidata nd;
1644    int res = do_path_lookup(AT_FDCWD, name, flags, &nd);
1645    if (!res)
1646        *path = nd.path;
1647    return res;
1648}
1649
1650/**
1651 * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
1652 * @dentry: pointer to dentry of the base directory
1653 * @mnt: pointer to vfs mount of the base directory
1654 * @name: pointer to file name
1655 * @flags: lookup flags
1656 * @nd: pointer to nameidata
1657 */
1658int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
1659            const char *name, unsigned int flags,
1660            struct nameidata *nd)
1661{
1662    nd->root.dentry = dentry;
1663    nd->root.mnt = mnt;
1664    /* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */
1665    return do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, nd);
1666}
1667
1668static struct dentry *__lookup_hash(struct qstr *name,
1669        struct dentry *base, struct nameidata *nd)
1670{
1671    struct inode *inode = base->d_inode;
1672    struct dentry *dentry;
1673    int err;
1674
1675    err = exec_permission(inode, 0);
1676    if (err)
1677        return ERR_PTR(err);
1678
1679    /*
1680     * Don't bother with __d_lookup: callers are for creat as
1681     * well as unlink, so a lot of the time it would cost
1682     * a double lookup.
1683     */
1684    dentry = d_lookup(base, name);
1685
1686    if (dentry && (dentry->d_flags & DCACHE_OP_REVALIDATE))
1687        dentry = do_revalidate(dentry, nd);
1688
1689    if (!dentry)
1690        dentry = d_alloc_and_lookup(base, name, nd);
1691
1692    return dentry;
1693}
1694
1695/*
1696 * Restricted form of lookup. Doesn't follow links, single-component only,
1697 * needs parent already locked. Doesn't follow mounts.
1698 * SMP-safe.
1699 */
1700static struct dentry *lookup_hash(struct nameidata *nd)
1701{
1702    return __lookup_hash(&nd->last, nd->path.dentry, nd);
1703}
1704
1705/**
1706 * lookup_one_len - filesystem helper to lookup single pathname component
1707 * @name: pathname component to lookup
1708 * @base: base directory to lookup from
1709 * @len: maximum length @len should be interpreted to
1710 *
1711 * Note that this routine is purely a helper for filesystem usage and should
1712 * not be called by generic code. Also note that by using this function the
1713 * nameidata argument is passed to the filesystem methods and a filesystem
1714 * using this helper needs to be prepared for that.
1715 */
1716struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
1717{
1718    struct qstr this;
1719    unsigned long hash;
1720    unsigned int c;
1721
1722    WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
1723
1724    this.name = name;
1725    this.len = len;
1726    if (!len)
1727        return ERR_PTR(-EACCES);
1728
1729    hash = init_name_hash();
1730    while (len--) {
1731        c = *(const unsigned char *)name++;
1732        if (c == '/' || c == '\0')
1733            return ERR_PTR(-EACCES);
1734        hash = partial_name_hash(c, hash);
1735    }
1736    this.hash = end_name_hash(hash);
1737    /*
1738     * See if the low-level filesystem might want
1739     * to use its own hash..
1740     */
1741    if (base->d_flags & DCACHE_OP_HASH) {
1742        int err = base->d_op->d_hash(base, base->d_inode, &this);
1743        if (err < 0)
1744            return ERR_PTR(err);
1745    }
1746
1747    return __lookup_hash(&this, base, NULL);
1748}
1749
1750int user_path_at(int dfd, const char __user *name, unsigned flags,
1751         struct path *path)
1752{
1753    struct nameidata nd;
1754    char *tmp = getname_flags(name, flags);
1755    int err = PTR_ERR(tmp);
1756    if (!IS_ERR(tmp)) {
1757
1758        BUG_ON(flags & LOOKUP_PARENT);
1759
1760        err = do_path_lookup(dfd, tmp, flags, &nd);
1761        putname(tmp);
1762        if (!err)
1763            *path = nd.path;
1764    }
1765    return err;
1766}
1767
1768static int user_path_parent(int dfd, const char __user *path,
1769            struct nameidata *nd, char **name)
1770{
1771    char *s = getname(path);
1772    int error;
1773
1774    if (IS_ERR(s))
1775        return PTR_ERR(s);
1776
1777    error = do_path_lookup(dfd, s, LOOKUP_PARENT, nd);
1778    if (error)
1779        putname(s);
1780    else
1781        *name = s;
1782
1783    return error;
1784}
1785
1786/*
1787 * It's inline, so penalty for filesystems that don't use sticky bit is
1788 * minimal.
1789 */
1790static inline int check_sticky(struct inode *dir, struct inode *inode)
1791{
1792    uid_t fsuid = current_fsuid();
1793
1794    if (!(dir->i_mode & S_ISVTX))
1795        return 0;
1796    if (current_user_ns() != inode_userns(inode))
1797        goto other_userns;
1798    if (inode->i_uid == fsuid)
1799        return 0;
1800    if (dir->i_uid == fsuid)
1801        return 0;
1802
1803other_userns:
1804    return !ns_capable(inode_userns(inode), CAP_FOWNER);
1805}
1806
1807/*
1808 * Check whether we can remove a link victim from directory dir, check
1809 * whether the type of victim is right.
1810 * 1. We can't do it if dir is read-only (done in permission())
1811 * 2. We should have write and exec permissions on dir
1812 * 3. We can't remove anything from append-only dir
1813 * 4. We can't do anything with immutable dir (done in permission())
1814 * 5. If the sticky bit on dir is set we should either
1815 * a. be owner of dir, or
1816 * b. be owner of victim, or
1817 * c. have CAP_FOWNER capability
1818 * 6. If the victim is append-only or immutable we can't do antyhing with
1819 * links pointing to it.
1820 * 7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
1821 * 8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
1822 * 9. We can't remove a root or mountpoint.
1823 * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
1824 * nfs_async_unlink().
1825 */
1826static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
1827{
1828    int error;
1829
1830    if (!victim->d_inode)
1831        return -ENOENT;
1832
1833    BUG_ON(victim->d_parent->d_inode != dir);
1834    audit_inode_child(victim, dir);
1835
1836    error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
1837    if (error)
1838        return error;
1839    if (IS_APPEND(dir))
1840        return -EPERM;
1841    if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
1842        IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
1843        return -EPERM;
1844    if (isdir) {
1845        if (!S_ISDIR(victim->d_inode->i_mode))
1846            return -ENOTDIR;
1847        if (IS_ROOT(victim))
1848            return -EBUSY;
1849    } else if (S_ISDIR(victim->d_inode->i_mode))
1850        return -EISDIR;
1851    if (IS_DEADDIR(dir))
1852        return -ENOENT;
1853    if (victim->d_flags & DCACHE_NFSFS_RENAMED)
1854        return -EBUSY;
1855    return 0;
1856}
1857
1858/* Check whether we can create an object with dentry child in directory
1859 * dir.
1860 * 1. We can't do it if child already exists (open has special treatment for
1861 * this case, but since we are inlined it's OK)
1862 * 2. We can't do it if dir is read-only (done in permission())
1863 * 3. We should have write and exec permissions on dir
1864 * 4. We can't do it if dir is immutable (done in permission())
1865 */
1866static inline int may_create(struct inode *dir, struct dentry *child)
1867{
1868    if (child->d_inode)
1869        return -EEXIST;
1870    if (IS_DEADDIR(dir))
1871        return -ENOENT;
1872    return inode_permission(dir, MAY_WRITE | MAY_EXEC);
1873}
1874
1875/*
1876 * p1 and p2 should be directories on the same fs.
1877 */
1878struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
1879{
1880    struct dentry *p;
1881
1882    if (p1 == p2) {
1883        mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
1884        return NULL;
1885    }
1886
1887    mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
1888
1889    p = d_ancestor(p2, p1);
1890    if (p) {
1891        mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
1892        mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
1893        return p;
1894    }
1895
1896    p = d_ancestor(p1, p2);
1897    if (p) {
1898        mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
1899        mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
1900        return p;
1901    }
1902
1903    mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
1904    mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
1905    return NULL;
1906}
1907
1908void unlock_rename(struct dentry *p1, struct dentry *p2)
1909{
1910    mutex_unlock(&p1->d_inode->i_mutex);
1911    if (p1 != p2) {
1912        mutex_unlock(&p2->d_inode->i_mutex);
1913        mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
1914    }
1915}
1916
1917int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
1918        struct nameidata *nd)
1919{
1920    int error = may_create(dir, dentry);
1921
1922    if (error)
1923        return error;
1924
1925    if (!dir->i_op->create)
1926        return -EACCES; /* shouldn't it be ENOSYS? */
1927    mode &= S_IALLUGO;
1928    mode |= S_IFREG;
1929    error = security_inode_create(dir, dentry, mode);
1930    if (error)
1931        return error;
1932    error = dir->i_op->create(dir, dentry, mode, nd);
1933    if (!error)
1934        fsnotify_create(dir, dentry);
1935    return error;
1936}
1937
1938static int may_open(struct path *path, int acc_mode, int flag)
1939{
1940    struct dentry *dentry = path->dentry;
1941    struct inode *inode = dentry->d_inode;
1942    int error;
1943
1944    /* O_PATH? */
1945    if (!acc_mode)
1946        return 0;
1947
1948    if (!inode)
1949        return -ENOENT;
1950
1951    switch (inode->i_mode & S_IFMT) {
1952    case S_IFLNK:
1953        return -ELOOP;
1954    case S_IFDIR:
1955        if (acc_mode & MAY_WRITE)
1956            return -EISDIR;
1957        break;
1958    case S_IFBLK:
1959    case S_IFCHR:
1960        if (path->mnt->mnt_flags & MNT_NODEV)
1961            return -EACCES;
1962        /*FALLTHRU*/
1963    case S_IFIFO:
1964    case S_IFSOCK:
1965        flag &= ~O_TRUNC;
1966        break;
1967    }
1968
1969    error = inode_permission(inode, acc_mode);
1970    if (error)
1971        return error;
1972
1973    /*
1974     * An append-only file must be opened in append mode for writing.
1975     */
1976    if (IS_APPEND(inode)) {
1977        if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
1978            return -EPERM;
1979        if (flag & O_TRUNC)
1980            return -EPERM;
1981    }
1982
1983    /* O_NOATIME can only be set by the owner or superuser */
1984    if (flag & O_NOATIME && !inode_owner_or_capable(inode))
1985        return -EPERM;
1986
1987    /*
1988     * Ensure there are no outstanding leases on the file.
1989     */
1990    return break_lease(inode, flag);
1991}
1992
1993static int handle_truncate(struct file *filp)
1994{
1995    struct path *path = &filp->f_path;
1996    struct inode *inode = path->dentry->d_inode;
1997    int error = get_write_access(inode);
1998    if (error)
1999        return error;
2000    /*
2001     * Refuse to truncate files with mandatory locks held on them.
2002     */
2003    error = locks_verify_locked(inode);
2004    if (!error)
2005        error = security_path_truncate(path);
2006    if (!error) {
2007        error = do_truncate(path->dentry, 0,
2008                    ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
2009                    filp);
2010    }
2011    put_write_access(inode);
2012    return error;
2013}
2014
2015/*
2016 * Note that while the flag value (low two bits) for sys_open means:
2017 * 00 - read-only
2018 * 01 - write-only
2019 * 10 - read-write
2020 * 11 - special
2021 * it is changed into
2022 * 00 - no permissions needed
2023 * 01 - read-permission
2024 * 10 - write-permission
2025 * 11 - read-write
2026 * for the internal routines (ie open_namei()/follow_link() etc)
2027 * This is more logical, and also allows the 00 "no perm needed"
2028 * to be used for symlinks (where the permissions are checked
2029 * later).
2030 *
2031*/
2032static inline int open_to_namei_flags(int flag)
2033{
2034    if ((flag+1) & O_ACCMODE)
2035        flag++;
2036    return flag;
2037}
2038
2039/*
2040 * Handle the last step of open()
2041 */
2042static struct file *do_last(struct nameidata *nd, struct path *path,
2043                const struct open_flags *op, const char *pathname)
2044{
2045    struct dentry *dir = nd->path.dentry;
2046    struct dentry *dentry;
2047    int open_flag = op->open_flag;
2048    int will_truncate = open_flag & O_TRUNC;
2049    int want_write = 0;
2050    int acc_mode = op->acc_mode;
2051    struct file *filp;
2052    int error;
2053
2054    nd->flags &= ~LOOKUP_PARENT;
2055    nd->flags |= op->intent;
2056
2057    switch (nd->last_type) {
2058    case LAST_DOTDOT:
2059    case LAST_DOT:
2060        error = handle_dots(nd, nd->last_type);
2061        if (error)
2062            return ERR_PTR(error);
2063        /* fallthrough */
2064    case LAST_ROOT:
2065        error = complete_walk(nd);
2066        if (error)
2067            return ERR_PTR(error);
2068        audit_inode(pathname, nd->path.dentry);
2069        if (open_flag & O_CREAT) {
2070            error = -EISDIR;
2071            goto exit;
2072        }
2073        goto ok;
2074    case LAST_BIND:
2075        error = complete_walk(nd);
2076        if (error)
2077            return ERR_PTR(error);
2078        audit_inode(pathname, dir);
2079        goto ok;
2080    }
2081
2082    if (!(open_flag & O_CREAT)) {
2083        int symlink_ok = 0;
2084        if (nd->last.name[nd->last.len])
2085            nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
2086        if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))
2087            symlink_ok = 1;
2088        /* we _can_ be in RCU mode here */
2089        error = walk_component(nd, path, &nd->last, LAST_NORM,
2090                    !symlink_ok);
2091        if (error < 0)
2092            return ERR_PTR(error);
2093        if (error) /* symlink */
2094            return NULL;
2095        /* sayonara */
2096        error = complete_walk(nd);
2097        if (error)
2098            return ERR_PTR(-ECHILD);
2099
2100        error = -ENOTDIR;
2101        if (nd->flags & LOOKUP_DIRECTORY) {
2102            if (!nd->inode->i_op->lookup)
2103                goto exit;
2104        }
2105        audit_inode(pathname, nd->path.dentry);
2106        goto ok;
2107    }
2108
2109    /* create side of things */
2110    error = complete_walk(nd);
2111    if (error)
2112        return ERR_PTR(error);
2113
2114    audit_inode(pathname, dir);
2115    error = -EISDIR;
2116    /* trailing slashes? */
2117    if (nd->last.name[nd->last.len])
2118        goto exit;
2119
2120    mutex_lock(&dir->d_inode->i_mutex);
2121
2122    dentry = lookup_hash(nd);
2123    error = PTR_ERR(dentry);
2124    if (IS_ERR(dentry)) {
2125        mutex_unlock(&dir->d_inode->i_mutex);
2126        goto exit;
2127    }
2128
2129    path->dentry = dentry;
2130    path->mnt = nd->path.mnt;
2131
2132    /* Negative dentry, just create the file */
2133    if (!dentry->d_inode) {
2134        int mode = op->mode;
2135        if (!IS_POSIXACL(dir->d_inode))
2136            mode &= ~current_umask();
2137        /*
2138         * This write is needed to ensure that a
2139         * rw->ro transition does not occur between
2140         * the time when the file is created and when
2141         * a permanent write count is taken through
2142         * the 'struct file' in nameidata_to_filp().
2143         */
2144        error = mnt_want_write(nd->path.mnt);
2145        if (error)
2146            goto exit_mutex_unlock;
2147        want_write = 1;
2148        /* Don't check for write permission, don't truncate */
2149        open_flag &= ~O_TRUNC;
2150        will_truncate = 0;
2151        acc_mode = MAY_OPEN;
2152        error = security_path_mknod(&nd->path, dentry, mode, 0);
2153        if (error)
2154            goto exit_mutex_unlock;
2155        error = vfs_create(dir->d_inode, dentry, mode, nd);
2156        if (error)
2157            goto exit_mutex_unlock;
2158        mutex_unlock(&dir->d_inode->i_mutex);
2159        dput(nd->path.dentry);
2160        nd->path.dentry = dentry;
2161        goto common;
2162    }
2163
2164    /*
2165     * It already exists.
2166     */
2167    mutex_unlock(&dir->d_inode->i_mutex);
2168    audit_inode(pathname, path->dentry);
2169
2170    error = -EEXIST;
2171    if (open_flag & O_EXCL)
2172        goto exit_dput;
2173
2174    error = follow_managed(path, nd->flags);
2175    if (error < 0)
2176        goto exit_dput;
2177
2178    error = -ENOENT;
2179    if (!path->dentry->d_inode)
2180        goto exit_dput;
2181
2182    if (path->dentry->d_inode->i_op->follow_link)
2183        return NULL;
2184
2185    path_to_nameidata(path, nd);
2186    nd->inode = path->dentry->d_inode;
2187    error = -EISDIR;
2188    if (S_ISDIR(nd->inode->i_mode))
2189        goto exit;
2190ok:
2191    if (!S_ISREG(nd->inode->i_mode))
2192        will_truncate = 0;
2193
2194    if (will_truncate) {
2195        error = mnt_want_write(nd->path.mnt);
2196        if (error)
2197            goto exit;
2198        want_write = 1;
2199    }
2200common:
2201    error = may_open(&nd->path, acc_mode, open_flag);
2202    if (error)
2203        goto exit;
2204    filp = nameidata_to_filp(nd);
2205    if (!IS_ERR(filp)) {
2206        error = ima_file_check(filp, op->acc_mode);
2207        if (error) {
2208            fput(filp);
2209            filp = ERR_PTR(error);
2210        }
2211    }
2212    if (!IS_ERR(filp)) {
2213        if (will_truncate) {
2214            error = handle_truncate(filp);
2215            if (error) {
2216                fput(filp);
2217                filp = ERR_PTR(error);
2218            }
2219        }
2220    }
2221out:
2222    if (want_write)
2223        mnt_drop_write(nd->path.mnt);
2224    path_put(&nd->path);
2225    return filp;
2226
2227exit_mutex_unlock:
2228    mutex_unlock(&dir->d_inode->i_mutex);
2229exit_dput:
2230    path_put_conditional(path, nd);
2231exit:
2232    filp = ERR_PTR(error);
2233    goto out;
2234}
2235
2236static struct file *path_openat(int dfd, const char *pathname,
2237        struct nameidata *nd, const struct open_flags *op, int flags)
2238{
2239    struct file *base = NULL;
2240    struct file *filp;
2241    struct path path;
2242    int error;
2243
2244    filp = get_empty_filp();
2245    if (!filp)
2246        return ERR_PTR(-ENFILE);
2247
2248    filp->f_flags = op->open_flag;
2249    nd->intent.open.file = filp;
2250    nd->intent.open.flags = open_to_namei_flags(op->open_flag);
2251    nd->intent.open.create_mode = op->mode;
2252
2253    error = path_init(dfd, pathname, flags | LOOKUP_PARENT, nd, &base);
2254    if (unlikely(error))
2255        goto out_filp;
2256
2257    current->total_link_count = 0;
2258    error = link_path_walk(pathname, nd);
2259    if (unlikely(error))
2260        goto out_filp;
2261
2262    filp = do_last(nd, &path, op, pathname);
2263    while (unlikely(!filp)) { /* trailing symlink */
2264        struct path link = path;
2265        void *cookie;
2266        if (!(nd->flags & LOOKUP_FOLLOW)) {
2267            path_put_conditional(&path, nd);
2268            path_put(&nd->path);
2269            filp = ERR_PTR(-ELOOP);
2270            break;
2271        }
2272        nd->flags |= LOOKUP_PARENT;
2273        nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
2274        error = follow_link(&link, nd, &cookie);
2275        if (unlikely(error))
2276            filp = ERR_PTR(error);
2277        else
2278            filp = do_last(nd, &path, op, pathname);
2279        put_link(nd, &link, cookie);
2280    }
2281out:
2282    if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT))
2283        path_put(&nd->root);
2284    if (base)
2285        fput(base);
2286    release_open_intent(nd);
2287    return filp;
2288
2289out_filp:
2290    filp = ERR_PTR(error);
2291    goto out;
2292}
2293
2294struct file *do_filp_open(int dfd, const char *pathname,
2295        const struct open_flags *op, int flags)
2296{
2297    struct nameidata nd;
2298    struct file *filp;
2299
2300    filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
2301    if (unlikely(filp == ERR_PTR(-ECHILD)))
2302        filp = path_openat(dfd, pathname, &nd, op, flags);
2303    if (unlikely(filp == ERR_PTR(-ESTALE)))
2304        filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
2305    return filp;
2306}
2307
2308struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
2309        const char *name, const struct open_flags *op, int flags)
2310{
2311    struct nameidata nd;
2312    struct file *file;
2313
2314    nd.root.mnt = mnt;
2315    nd.root.dentry = dentry;
2316
2317    flags |= LOOKUP_ROOT;
2318
2319    if (dentry->d_inode->i_op->follow_link && op->intent & LOOKUP_OPEN)
2320        return ERR_PTR(-ELOOP);
2321
2322    file = path_openat(-1, name, &nd, op, flags | LOOKUP_RCU);
2323    if (unlikely(file == ERR_PTR(-ECHILD)))
2324        file = path_openat(-1, name, &nd, op, flags);
2325    if (unlikely(file == ERR_PTR(-ESTALE)))
2326        file = path_openat(-1, name, &nd, op, flags | LOOKUP_REVAL);
2327    return file;
2328}
2329
2330/**
2331 * lookup_create - lookup a dentry, creating it if it doesn't exist
2332 * @nd: nameidata info
2333 * @is_dir: directory flag
2334 *
2335 * Simple function to lookup and return a dentry and create it
2336 * if it doesn't exist. Is SMP-safe.
2337 *
2338 * Returns with nd->path.dentry->d_inode->i_mutex locked.
2339 */
2340struct dentry *lookup_create(struct nameidata *nd, int is_dir)
2341{
2342    struct dentry *dentry = ERR_PTR(-EEXIST);
2343
2344    mutex_lock_nested(&nd->path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
2345    /*
2346     * Yucky last component or no last component at all?
2347     * (foo/., foo/.., /////)
2348     */
2349    if (nd->last_type != LAST_NORM)
2350        goto fail;
2351    nd->flags &= ~LOOKUP_PARENT;
2352    nd->flags |= LOOKUP_CREATE | LOOKUP_EXCL;
2353    nd->intent.open.flags = O_EXCL;
2354
2355    /*
2356     * Do the final lookup.
2357     */
2358    dentry = lookup_hash(nd);
2359    if (IS_ERR(dentry))
2360        goto fail;
2361
2362    if (dentry->d_inode)
2363        goto eexist;
2364    /*
2365     * Special case - lookup gave negative, but... we had foo/bar/
2366     * From the vfs_mknod() POV we just have a negative dentry -
2367     * all is fine. Let's be bastards - you had / on the end, you've
2368     * been asking for (non-existent) directory. -ENOENT for you.
2369     */
2370    if (unlikely(!is_dir && nd->last.name[nd->last.len])) {
2371        dput(dentry);
2372        dentry = ERR_PTR(-ENOENT);
2373    }
2374    return dentry;
2375eexist:
2376    dput(dentry);
2377    dentry = ERR_PTR(-EEXIST);
2378fail:
2379    return dentry;
2380}
2381EXPORT_SYMBOL_GPL(lookup_create);
2382
2383int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
2384{
2385    int error = may_create(dir, dentry);
2386
2387    if (error)
2388        return error;
2389
2390    if ((S_ISCHR(mode) || S_ISBLK(mode)) &&
2391        !ns_capable(inode_userns(dir), CAP_MKNOD))
2392        return -EPERM;
2393
2394    if (!dir->i_op->mknod)
2395        return -EPERM;
2396
2397    error = devcgroup_inode_mknod(mode, dev);
2398    if (error)
2399        return error;
2400
2401    error = security_inode_mknod(dir, dentry, mode, dev);
2402    if (error)
2403        return error;
2404
2405    error = dir->i_op->mknod(dir, dentry, mode, dev);
2406    if (!error)
2407        fsnotify_create(dir, dentry);
2408    return error;
2409}
2410
2411static int may_mknod(mode_t mode)
2412{
2413    switch (mode & S_IFMT) {
2414    case S_IFREG:
2415    case S_IFCHR:
2416    case S_IFBLK:
2417    case S_IFIFO:
2418    case S_IFSOCK:
2419    case 0: /* zero mode translates to S_IFREG */
2420        return 0;
2421    case S_IFDIR:
2422        return -EPERM;
2423    default:
2424        return -EINVAL;
2425    }
2426}
2427
2428SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, int, mode,
2429        unsigned, dev)
2430{
2431    int error;
2432    char *tmp;
2433    struct dentry *dentry;
2434    struct nameidata nd;
2435
2436    if (S_ISDIR(mode))
2437        return -EPERM;
2438
2439    error = user_path_parent(dfd, filename, &nd, &tmp);
2440    if (error)
2441        return error;
2442
2443    dentry = lookup_create(&nd, 0);
2444    if (IS_ERR(dentry)) {
2445        error = PTR_ERR(dentry);
2446        goto out_unlock;
2447    }
2448    if (!IS_POSIXACL(nd.path.dentry->d_inode))
2449        mode &= ~current_umask();
2450    error = may_mknod(mode);
2451    if (error)
2452        goto out_dput;
2453    error = mnt_want_write(nd.path.mnt);
2454    if (error)
2455        goto out_dput;
2456    error = security_path_mknod(&nd.path, dentry, mode, dev);
2457    if (error)
2458        goto out_drop_write;
2459    switch (mode & S_IFMT) {
2460        case 0: case S_IFREG:
2461            error = vfs_create(nd.path.dentry->d_inode,dentry,mode,&nd);
2462            break;
2463        case S_IFCHR: case S_IFBLK:
2464            error = vfs_mknod(nd.path.dentry->d_inode,dentry,mode,
2465                    new_decode_dev(dev));
2466            break;
2467        case S_IFIFO: case S_IFSOCK:
2468            error = vfs_mknod(nd.path.dentry->d_inode,dentry,mode,0);
2469            break;
2470    }
2471out_drop_write:
2472    mnt_drop_write(nd.path.mnt);
2473out_dput:
2474    dput(dentry);
2475out_unlock:
2476    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2477    path_put(&nd.path);
2478    putname(tmp);
2479
2480    return error;
2481}
2482
2483SYSCALL_DEFINE3(mknod, const char __user *, filename, int, mode, unsigned, dev)
2484{
2485    return sys_mknodat(AT_FDCWD, filename, mode, dev);
2486}
2487
2488int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
2489{
2490    int error = may_create(dir, dentry);
2491
2492    if (error)
2493        return error;
2494
2495    if (!dir->i_op->mkdir)
2496        return -EPERM;
2497
2498    mode &= (S_IRWXUGO|S_ISVTX);
2499    error = security_inode_mkdir(dir, dentry, mode);
2500    if (error)
2501        return error;
2502
2503    error = dir->i_op->mkdir(dir, dentry, mode);
2504    if (!error)
2505        fsnotify_mkdir(dir, dentry);
2506    return error;
2507}
2508
2509SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, int, mode)
2510{
2511    int error = 0;
2512    char * tmp;
2513    struct dentry *dentry;
2514    struct nameidata nd;
2515
2516    error = user_path_parent(dfd, pathname, &nd, &tmp);
2517    if (error)
2518        goto out_err;
2519
2520    dentry = lookup_create(&nd, 1);
2521    error = PTR_ERR(dentry);
2522    if (IS_ERR(dentry))
2523        goto out_unlock;
2524
2525    if (!IS_POSIXACL(nd.path.dentry->d_inode))
2526        mode &= ~current_umask();
2527    error = mnt_want_write(nd.path.mnt);
2528    if (error)
2529        goto out_dput;
2530    error = security_path_mkdir(&nd.path, dentry, mode);
2531    if (error)
2532        goto out_drop_write;
2533    error = vfs_mkdir(nd.path.dentry->d_inode, dentry, mode);
2534out_drop_write:
2535    mnt_drop_write(nd.path.mnt);
2536out_dput:
2537    dput(dentry);
2538out_unlock:
2539    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2540    path_put(&nd.path);
2541    putname(tmp);
2542out_err:
2543    return error;
2544}
2545
2546SYSCALL_DEFINE2(mkdir, const char __user *, pathname, int, mode)
2547{
2548    return sys_mkdirat(AT_FDCWD, pathname, mode);
2549}
2550
2551/*
2552 * The dentry_unhash() helper will try to drop the dentry early: we
2553 * should have a usage count of 2 if we're the only user of this
2554 * dentry, and if that is true (possibly after pruning the dcache),
2555 * then we drop the dentry now.
2556 *
2557 * A low-level filesystem can, if it choses, legally
2558 * do a
2559 *
2560 * if (!d_unhashed(dentry))
2561 * return -EBUSY;
2562 *
2563 * if it cannot handle the case of removing a directory
2564 * that is still in use by something else..
2565 */
2566void dentry_unhash(struct dentry *dentry)
2567{
2568    shrink_dcache_parent(dentry);
2569    spin_lock(&dentry->d_lock);
2570    if (dentry->d_count == 1)
2571        __d_drop(dentry);
2572    spin_unlock(&dentry->d_lock);
2573}
2574
2575int vfs_rmdir(struct inode *dir, struct dentry *dentry)
2576{
2577    int error = may_delete(dir, dentry, 1);
2578
2579    if (error)
2580        return error;
2581
2582    if (!dir->i_op->rmdir)
2583        return -EPERM;
2584
2585    mutex_lock(&dentry->d_inode->i_mutex);
2586
2587    error = -EBUSY;
2588    if (d_mountpoint(dentry))
2589        goto out;
2590
2591    error = security_inode_rmdir(dir, dentry);
2592    if (error)
2593        goto out;
2594
2595    shrink_dcache_parent(dentry);
2596    error = dir->i_op->rmdir(dir, dentry);
2597    if (error)
2598        goto out;
2599
2600    dentry->d_inode->i_flags |= S_DEAD;
2601    dont_mount(dentry);
2602
2603out:
2604    mutex_unlock(&dentry->d_inode->i_mutex);
2605    if (!error)
2606        d_delete(dentry);
2607    return error;
2608}
2609
2610static long do_rmdir(int dfd, const char __user *pathname)
2611{
2612    int error = 0;
2613    char * name;
2614    struct dentry *dentry;
2615    struct nameidata nd;
2616
2617    error = user_path_parent(dfd, pathname, &nd, &name);
2618    if (error)
2619        return error;
2620
2621    switch(nd.last_type) {
2622    case LAST_DOTDOT:
2623        error = -ENOTEMPTY;
2624        goto exit1;
2625    case LAST_DOT:
2626        error = -EINVAL;
2627        goto exit1;
2628    case LAST_ROOT:
2629        error = -EBUSY;
2630        goto exit1;
2631    }
2632
2633    nd.flags &= ~LOOKUP_PARENT;
2634
2635    mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
2636    dentry = lookup_hash(&nd);
2637    error = PTR_ERR(dentry);
2638    if (IS_ERR(dentry))
2639        goto exit2;
2640    if (!dentry->d_inode) {
2641        error = -ENOENT;
2642        goto exit3;
2643    }
2644    error = mnt_want_write(nd.path.mnt);
2645    if (error)
2646        goto exit3;
2647    error = security_path_rmdir(&nd.path, dentry);
2648    if (error)
2649        goto exit4;
2650    error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
2651exit4:
2652    mnt_drop_write(nd.path.mnt);
2653exit3:
2654    dput(dentry);
2655exit2:
2656    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2657exit1:
2658    path_put(&nd.path);
2659    putname(name);
2660    return error;
2661}
2662
2663SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
2664{
2665    return do_rmdir(AT_FDCWD, pathname);
2666}
2667
2668int vfs_unlink(struct inode *dir, struct dentry *dentry)
2669{
2670    int error = may_delete(dir, dentry, 0);
2671
2672    if (error)
2673        return error;
2674
2675    if (!dir->i_op->unlink)
2676        return -EPERM;
2677
2678    mutex_lock(&dentry->d_inode->i_mutex);
2679    if (d_mountpoint(dentry))
2680        error = -EBUSY;
2681    else {
2682        error = security_inode_unlink(dir, dentry);
2683        if (!error) {
2684            error = dir->i_op->unlink(dir, dentry);
2685            if (!error)
2686                dont_mount(dentry);
2687        }
2688    }
2689    mutex_unlock(&dentry->d_inode->i_mutex);
2690
2691    /* We don't d_delete() NFS sillyrenamed files--they still exist. */
2692    if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
2693        fsnotify_link_count(dentry->d_inode);
2694        d_delete(dentry);
2695    }
2696
2697    return error;
2698}
2699
2700/*
2701 * Make sure that the actual truncation of the file will occur outside its
2702 * directory's i_mutex. Truncate can take a long time if there is a lot of
2703 * writeout happening, and we don't want to prevent access to the directory
2704 * while waiting on the I/O.
2705 */
2706static long do_unlinkat(int dfd, const char __user *pathname)
2707{
2708    int error;
2709    char *name;
2710    struct dentry *dentry;
2711    struct nameidata nd;
2712    struct inode *inode = NULL;
2713
2714    error = user_path_parent(dfd, pathname, &nd, &name);
2715    if (error)
2716        return error;
2717
2718    error = -EISDIR;
2719    if (nd.last_type != LAST_NORM)
2720        goto exit1;
2721
2722    nd.flags &= ~LOOKUP_PARENT;
2723
2724    mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
2725    dentry = lookup_hash(&nd);
2726    error = PTR_ERR(dentry);
2727    if (!IS_ERR(dentry)) {
2728        /* Why not before? Because we want correct error value */
2729        if (nd.last.name[nd.last.len])
2730            goto slashes;
2731        inode = dentry->d_inode;
2732        if (!inode)
2733            goto slashes;
2734        ihold(inode);
2735        error = mnt_want_write(nd.path.mnt);
2736        if (error)
2737            goto exit2;
2738        error = security_path_unlink(&nd.path, dentry);
2739        if (error)
2740            goto exit3;
2741        error = vfs_unlink(nd.path.dentry->d_inode, dentry);
2742exit3:
2743        mnt_drop_write(nd.path.mnt);
2744    exit2:
2745        dput(dentry);
2746    }
2747    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2748    if (inode)
2749        iput(inode); /* truncate the inode here */
2750exit1:
2751    path_put(&nd.path);
2752    putname(name);
2753    return error;
2754
2755slashes:
2756    error = !dentry->d_inode ? -ENOENT :
2757        S_ISDIR(dentry->d_inode->i_mode) ? -EISDIR : -ENOTDIR;
2758    goto exit2;
2759}
2760
2761SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
2762{
2763    if ((flag & ~AT_REMOVEDIR) != 0)
2764        return -EINVAL;
2765
2766    if (flag & AT_REMOVEDIR)
2767        return do_rmdir(dfd, pathname);
2768
2769    return do_unlinkat(dfd, pathname);
2770}
2771
2772SYSCALL_DEFINE1(unlink, const char __user *, pathname)
2773{
2774    return do_unlinkat(AT_FDCWD, pathname);
2775}
2776
2777int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
2778{
2779    int error = may_create(dir, dentry);
2780
2781    if (error)
2782        return error;
2783
2784    if (!dir->i_op->symlink)
2785        return -EPERM;
2786
2787    error = security_inode_symlink(dir, dentry, oldname);
2788    if (error)
2789        return error;
2790
2791    error = dir->i_op->symlink(dir, dentry, oldname);
2792    if (!error)
2793        fsnotify_create(dir, dentry);
2794    return error;
2795}
2796
2797SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
2798        int, newdfd, const char __user *, newname)
2799{
2800    int error;
2801    char *from;
2802    char *to;
2803    struct dentry *dentry;
2804    struct nameidata nd;
2805
2806    from = getname(oldname);
2807    if (IS_ERR(from))
2808        return PTR_ERR(from);
2809
2810    error = user_path_parent(newdfd, newname, &nd, &to);
2811    if (error)
2812        goto out_putname;
2813
2814    dentry = lookup_create(&nd, 0);
2815    error = PTR_ERR(dentry);
2816    if (IS_ERR(dentry))
2817        goto out_unlock;
2818
2819    error = mnt_want_write(nd.path.mnt);
2820    if (error)
2821        goto out_dput;
2822    error = security_path_symlink(&nd.path, dentry, from);
2823    if (error)
2824        goto out_drop_write;
2825    error = vfs_symlink(nd.path.dentry->d_inode, dentry, from);
2826out_drop_write:
2827    mnt_drop_write(nd.path.mnt);
2828out_dput:
2829    dput(dentry);
2830out_unlock:
2831    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2832    path_put(&nd.path);
2833    putname(to);
2834out_putname:
2835    putname(from);
2836    return error;
2837}
2838
2839SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
2840{
2841    return sys_symlinkat(oldname, AT_FDCWD, newname);
2842}
2843
2844int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry)
2845{
2846    struct inode *inode = old_dentry->d_inode;
2847    int error;
2848
2849    if (!inode)
2850        return -ENOENT;
2851
2852    error = may_create(dir, new_dentry);
2853    if (error)
2854        return error;
2855
2856    if (dir->i_sb != inode->i_sb)
2857        return -EXDEV;
2858
2859    /*
2860     * A link to an append-only or immutable file cannot be created.
2861     */
2862    if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
2863        return -EPERM;
2864    if (!dir->i_op->link)
2865        return -EPERM;
2866    if (S_ISDIR(inode->i_mode))
2867        return -EPERM;
2868
2869    error = security_inode_link(old_dentry, dir, new_dentry);
2870    if (error)
2871        return error;
2872
2873    mutex_lock(&inode->i_mutex);
2874    /* Make sure we don't allow creating hardlink to an unlinked file */
2875    if (inode->i_nlink == 0)
2876        error = -ENOENT;
2877    else
2878        error = dir->i_op->link(old_dentry, dir, new_dentry);
2879    mutex_unlock(&inode->i_mutex);
2880    if (!error)
2881        fsnotify_link(dir, inode, new_dentry);
2882    return error;
2883}
2884
2885/*
2886 * Hardlinks are often used in delicate situations. We avoid
2887 * security-related surprises by not following symlinks on the
2888 * newname. --KAB
2889 *
2890 * We don't follow them on the oldname either to be compatible
2891 * with linux 2.0, and to avoid hard-linking to directories
2892 * and other special files. --ADM
2893 */
2894SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
2895        int, newdfd, const char __user *, newname, int, flags)
2896{
2897    struct dentry *new_dentry;
2898    struct nameidata nd;
2899    struct path old_path;
2900    int how = 0;
2901    int error;
2902    char *to;
2903
2904    if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
2905        return -EINVAL;
2906    /*
2907     * To use null names we require CAP_DAC_READ_SEARCH
2908     * This ensures that not everyone will be able to create
2909     * handlink using the passed filedescriptor.
2910     */
2911    if (flags & AT_EMPTY_PATH) {
2912        if (!capable(CAP_DAC_READ_SEARCH))
2913            return -ENOENT;
2914        how = LOOKUP_EMPTY;
2915    }
2916
2917    if (flags & AT_SYMLINK_FOLLOW)
2918        how |= LOOKUP_FOLLOW;
2919
2920    error = user_path_at(olddfd, oldname, how, &old_path);
2921    if (error)
2922        return error;
2923
2924    error = user_path_parent(newdfd, newname, &nd, &to);
2925    if (error)
2926        goto out;
2927    error = -EXDEV;
2928    if (old_path.mnt != nd.path.mnt)
2929        goto out_release;
2930    new_dentry = lookup_create(&nd, 0);
2931    error = PTR_ERR(new_dentry);
2932    if (IS_ERR(new_dentry))
2933        goto out_unlock;
2934    error = mnt_want_write(nd.path.mnt);
2935    if (error)
2936        goto out_dput;
2937    error = security_path_link(old_path.dentry, &nd.path, new_dentry);
2938    if (error)
2939        goto out_drop_write;
2940    error = vfs_link(old_path.dentry, nd.path.dentry->d_inode, new_dentry);
2941out_drop_write:
2942    mnt_drop_write(nd.path.mnt);
2943out_dput:
2944    dput(new_dentry);
2945out_unlock:
2946    mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
2947out_release:
2948    path_put(&nd.path);
2949    putname(to);
2950out:
2951    path_put(&old_path);
2952
2953    return error;
2954}
2955
2956SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
2957{
2958    return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
2959}
2960
2961/*
2962 * The worst of all namespace operations - renaming directory. "Perverted"
2963 * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
2964 * Problems:
2965 * a) we can get into loop creation. Check is done in is_subdir().
2966 * b) race potential - two innocent renames can create a loop together.
2967 * That's where 4.4 screws up. Current fix: serialization on
2968 * sb->s_vfs_rename_mutex. We might be more accurate, but that's another
2969 * story.
2970 * c) we have to lock _three_ objects - parents and victim (if it exists).
2971 * And that - after we got ->i_mutex on parents (until then we don't know
2972 * whether the target exists). Solution: try to be smart with locking
2973 * order for inodes. We rely on the fact that tree topology may change
2974 * only under ->s_vfs_rename_mutex _and_ that parent of the object we
2975 * move will be locked. Thus we can rank directories by the tree
2976 * (ancestors first) and rank all non-directories after them.
2977 * That works since everybody except rename does "lock parent, lookup,
2978 * lock child" and rename is under ->s_vfs_rename_mutex.
2979 * HOWEVER, it relies on the assumption that any object with ->lookup()
2980 * has no more than 1 dentry. If "hybrid" objects will ever appear,
2981 * we'd better make sure that there's no link(2) for them.
2982 * d) conversion from fhandle to dentry may come in the wrong moment - when
2983 * we are removing the target. Solution: we will have to grab ->i_mutex
2984 * in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
2985 * ->i_mutex on parents, which works but leads to some truly excessive
2986 * locking].
2987 */
2988static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
2989              struct inode *new_dir, struct dentry *new_dentry)
2990{
2991    int error = 0;
2992    struct inode *target = new_dentry->d_inode;
2993
2994    /*
2995     * If we are going to change the parent - check write permissions,
2996     * we'll need to flip '..'.
2997     */
2998    if (new_dir != old_dir) {
2999        error = inode_permission(old_dentry->d_inode, MAY_WRITE);
3000        if (error)
3001            return error;
3002    }
3003
3004    error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
3005    if (error)
3006        return error;
3007
3008    if (target)
3009        mutex_lock(&target->i_mutex);
3010
3011    error = -EBUSY;
3012    if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
3013        goto out;
3014
3015    if (target)
3016        shrink_dcache_parent(new_dentry);
3017    error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
3018    if (error)
3019        goto out;
3020
3021    if (target) {
3022        target->i_flags |= S_DEAD;
3023        dont_mount(new_dentry);
3024    }
3025out:
3026    if (target)
3027        mutex_unlock(&target->i_mutex);
3028    if (!error)
3029        if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
3030            d_move(old_dentry,new_dentry);
3031    return error;
3032}
3033
3034static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
3035                struct inode *new_dir, struct dentry *new_dentry)
3036{
3037    struct inode *target = new_dentry->d_inode;
3038    int error;
3039
3040    error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
3041    if (error)
3042        return error;
3043
3044    dget(new_dentry);
3045    if (target)
3046        mutex_lock(&target->i_mutex);
3047
3048    error = -EBUSY;
3049    if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry))
3050        goto out;
3051
3052    error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
3053    if (error)
3054        goto out;
3055
3056    if (target)
3057        dont_mount(new_dentry);
3058    if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
3059        d_move(old_dentry, new_dentry);
3060out:
3061    if (target)
3062        mutex_unlock(&target->i_mutex);
3063    dput(new_dentry);
3064    return error;
3065}
3066
3067int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
3068           struct inode *new_dir, struct dentry *new_dentry)
3069{
3070    int error;
3071    int is_dir = S_ISDIR(old_dentry->d_inode->i_mode);
3072    const unsigned char *old_name;
3073
3074    if (old_dentry->d_inode == new_dentry->d_inode)
3075         return 0;
3076 
3077    error = may_delete(old_dir, old_dentry, is_dir);
3078    if (error)
3079        return error;
3080
3081    if (!new_dentry->d_inode)
3082        error = may_create(new_dir, new_dentry);
3083    else
3084        error = may_delete(new_dir, new_dentry, is_dir);
3085    if (error)
3086        return error;
3087
3088    if (!old_dir->i_op->rename)
3089        return -EPERM;
3090
3091    old_name = fsnotify_oldname_init(old_dentry->d_name.name);
3092
3093    if (is_dir)
3094        error = vfs_rename_dir(old_dir,old_dentry,new_dir,new_dentry);
3095    else
3096        error = vfs_rename_other(old_dir,old_dentry,new_dir,new_dentry);
3097    if (!error)
3098        fsnotify_move(old_dir, new_dir, old_name, is_dir,
3099                  new_dentry->d_inode, old_dentry);
3100    fsnotify_oldname_free(old_name);
3101
3102    return error;
3103}
3104
3105SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
3106        int, newdfd, const char __user *, newname)
3107{
3108    struct dentry *old_dir, *new_dir;
3109    struct dentry *old_dentry, *new_dentry;
3110    struct dentry *trap;
3111    struct nameidata oldnd, newnd;
3112    char *from;
3113    char *to;
3114    int error;
3115
3116    error = user_path_parent(olddfd, oldname, &oldnd, &from);
3117    if (error)
3118        goto exit;
3119
3120    error = user_path_parent(newdfd, newname, &newnd, &to);
3121    if (error)
3122        goto exit1;
3123
3124    error = -EXDEV;
3125    if (oldnd.path.mnt != newnd.path.mnt)
3126        goto exit2;
3127
3128    old_dir = oldnd.path.dentry;
3129    error = -EBUSY;
3130    if (oldnd.last_type != LAST_NORM)
3131        goto exit2;
3132
3133    new_dir = newnd.path.dentry;
3134    if (newnd.last_type != LAST_NORM)
3135        goto exit2;
3136
3137    oldnd.flags &= ~LOOKUP_PARENT;
3138    newnd.flags &= ~LOOKUP_PARENT;
3139    newnd.flags |= LOOKUP_RENAME_TARGET;
3140
3141    trap = lock_rename(new_dir, old_dir);
3142
3143    old_dentry = lookup_hash(&oldnd);
3144    error = PTR_ERR(old_dentry);
3145    if (IS_ERR(old_dentry))
3146        goto exit3;
3147    /* source must exist */
3148    error = -ENOENT;
3149    if (!old_dentry->d_inode)
3150        goto exit4;
3151    /* unless the source is a directory trailing slashes give -ENOTDIR */
3152    if (!S_ISDIR(old_dentry->d_inode->i_mode)) {
3153        error = -ENOTDIR;
3154        if (oldnd.last.name[oldnd.last.len])
3155            goto exit4;
3156        if (newnd.last.name[newnd.last.len])
3157            goto exit4;
3158    }
3159    /* source should not be ancestor of target */
3160    error = -EINVAL;
3161    if (old_dentry == trap)
3162        goto exit4;
3163    new_dentry = lookup_hash(&newnd);
3164    error = PTR_ERR(new_dentry);
3165    if (IS_ERR(new_dentry))
3166        goto exit4;
3167    /* target should not be an ancestor of source */
3168    error = -ENOTEMPTY;
3169    if (new_dentry == trap)
3170        goto exit5;
3171
3172    error = mnt_want_write(oldnd.path.mnt);
3173    if (error)
3174        goto exit5;
3175    error = security_path_rename(&oldnd.path, old_dentry,
3176                     &newnd.path, new_dentry);
3177    if (error)
3178        goto exit6;
3179    error = vfs_rename(old_dir->d_inode, old_dentry,
3180                   new_dir->d_inode, new_dentry);
3181exit6:
3182    mnt_drop_write(oldnd.path.mnt);
3183exit5:
3184    dput(new_dentry);
3185exit4:
3186    dput(old_dentry);
3187exit3:
3188    unlock_rename(new_dir, old_dir);
3189exit2:
3190    path_put(&newnd.path);
3191    putname(to);
3192exit1:
3193    path_put(&oldnd.path);
3194    putname(from);
3195exit:
3196    return error;
3197}
3198
3199SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
3200{
3201    return sys_renameat(AT_FDCWD, oldname, AT_FDCWD, newname);
3202}
3203
3204int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen, const char *link)
3205{
3206    int len;
3207
3208    len = PTR_ERR(link);
3209    if (IS_ERR(link))
3210        goto out;
3211
3212    len = strlen(link);
3213    if (len > (unsigned) buflen)
3214        len = buflen;
3215    if (copy_to_user(buffer, link, len))
3216        len = -EFAULT;
3217out:
3218    return len;
3219}
3220
3221/*
3222 * A helper for ->readlink(). This should be used *ONLY* for symlinks that
3223 * have ->follow_link() touching nd only in nd_set_link(). Using (or not
3224 * using) it for any given inode is up to filesystem.
3225 */
3226int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
3227{
3228    struct nameidata nd;
3229    void *cookie;
3230    int res;
3231
3232    nd.depth = 0;
3233    cookie = dentry->d_inode->i_op->follow_link(dentry, &nd);
3234    if (IS_ERR(cookie))
3235        return PTR_ERR(cookie);
3236
3237    res = vfs_readlink(dentry, buffer, buflen, nd_get_link(&nd));
3238    if (dentry->d_inode->i_op->put_link)
3239        dentry->d_inode->i_op->put_link(dentry, &nd, cookie);
3240    return res;
3241}
3242
3243int vfs_follow_link(struct nameidata *nd, const char *link)
3244{
3245    return __vfs_follow_link(nd, link);
3246}
3247
3248/* get the link contents into pagecache */
3249static char *page_getlink(struct dentry * dentry, struct page **ppage)
3250{
3251    char *kaddr;
3252    struct page *page;
3253    struct address_space *mapping = dentry->d_inode->i_mapping;
3254    page = read_mapping_page(mapping, 0, NULL);
3255    if (IS_ERR(page))
3256        return (char*)page;
3257    *ppage = page;
3258    kaddr = kmap(page);
3259    nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
3260    return kaddr;
3261}
3262
3263int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
3264{
3265    struct page *page = NULL;
3266    char *s = page_getlink(dentry, &page);
3267    int res = vfs_readlink(dentry,buffer,buflen,s);
3268    if (page) {
3269        kunmap(page);
3270        page_cache_release(page);
3271    }
3272    return res;
3273}
3274
3275void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd)
3276{
3277    struct page *page = NULL;
3278    nd_set_link(nd, page_getlink(dentry, &page));
3279    return page;
3280}
3281
3282void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
3283{
3284    struct page *page = cookie;
3285
3286    if (page) {
3287        kunmap(page);
3288        page_cache_release(page);
3289    }
3290}
3291
3292/*
3293 * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
3294 */
3295int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
3296{
3297    struct address_space *mapping = inode->i_mapping;
3298    struct page *page;
3299    void *fsdata;
3300    int err;
3301    char *kaddr;
3302    unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE;
3303    if (nofs)
3304        flags |= AOP_FLAG_NOFS;
3305
3306retry:
3307    err = pagecache_write_begin(NULL, mapping, 0, len-1,
3308                flags, &page, &fsdata);
3309    if (err)
3310        goto fail;
3311
3312    kaddr = kmap_atomic(page, KM_USER0);
3313    memcpy(kaddr, symname, len-1);
3314    kunmap_atomic(kaddr, KM_USER0);
3315
3316    err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
3317                            page, fsdata);
3318    if (err < 0)
3319        goto fail;
3320    if (err < len-1)
3321        goto retry;
3322
3323    mark_inode_dirty(inode);
3324    return 0;
3325fail:
3326    return err;
3327}
3328
3329int page_symlink(struct inode *inode, const char *symname, int len)
3330{
3331    return __page_symlink(inode, symname, len,
3332            !(mapping_gfp_mask(inode->i_mapping) & __GFP_FS));
3333}
3334
3335const struct inode_operations page_symlink_inode_operations = {
3336    .readlink = generic_readlink,
3337    .follow_link = page_follow_link_light,
3338    .put_link = page_put_link,
3339};
3340
3341EXPORT_SYMBOL(user_path_at);
3342EXPORT_SYMBOL(follow_down_one);
3343EXPORT_SYMBOL(follow_down);
3344EXPORT_SYMBOL(follow_up);
3345EXPORT_SYMBOL(get_write_access); /* binfmt_aout */
3346EXPORT_SYMBOL(getname);
3347EXPORT_SYMBOL(lock_rename);
3348EXPORT_SYMBOL(lookup_one_len);
3349EXPORT_SYMBOL(page_follow_link_light);
3350EXPORT_SYMBOL(page_put_link);
3351EXPORT_SYMBOL(page_readlink);
3352EXPORT_SYMBOL(__page_symlink);
3353EXPORT_SYMBOL(page_symlink);
3354EXPORT_SYMBOL(page_symlink_inode_operations);
3355EXPORT_SYMBOL(kern_path_parent);
3356EXPORT_SYMBOL(kern_path);
3357EXPORT_SYMBOL(vfs_path_lookup);
3358EXPORT_SYMBOL(inode_permission);
3359EXPORT_SYMBOL(file_permission);
3360EXPORT_SYMBOL(unlock_rename);
3361EXPORT_SYMBOL(vfs_create);
3362EXPORT_SYMBOL(vfs_follow_link);
3363EXPORT_SYMBOL(vfs_link);
3364EXPORT_SYMBOL(vfs_mkdir);
3365EXPORT_SYMBOL(vfs_mknod);
3366EXPORT_SYMBOL(generic_permission);
3367EXPORT_SYMBOL(vfs_readlink);
3368EXPORT_SYMBOL(vfs_rename);
3369EXPORT_SYMBOL(vfs_rmdir);
3370EXPORT_SYMBOL(vfs_symlink);
3371EXPORT_SYMBOL(vfs_unlink);
3372EXPORT_SYMBOL(dentry_unhash);
3373EXPORT_SYMBOL(generic_readlink);
3374

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