Root/fs/namespace.c

Source at commit 9845c1745d3d531a5b9544f5322c62bfb4d4e9bc created 1 year 3 months ago.
By Xiangfu, rtc: jz4740 fix hwclock give time out
1/*
2 * linux/fs/namespace.c
3 *
4 * (C) Copyright Al Viro 2000, 2001
5 * Released under GPL v2.
6 *
7 * Based on code from fs/super.c, copyright Linus Torvalds and others.
8 * Heavily rewritten.
9 */
10
11#include <linux/syscalls.h>
12#include <linux/slab.h>
13#include <linux/sched.h>
14#include <linux/spinlock.h>
15#include <linux/percpu.h>
16#include <linux/init.h>
17#include <linux/kernel.h>
18#include <linux/acct.h>
19#include <linux/capability.h>
20#include <linux/cpumask.h>
21#include <linux/module.h>
22#include <linux/sysfs.h>
23#include <linux/seq_file.h>
24#include <linux/mnt_namespace.h>
25#include <linux/namei.h>
26#include <linux/nsproxy.h>
27#include <linux/security.h>
28#include <linux/mount.h>
29#include <linux/ramfs.h>
30#include <linux/log2.h>
31#include <linux/idr.h>
32#include <linux/fs_struct.h>
33#include <linux/fsnotify.h>
34#include <asm/uaccess.h>
35#include <asm/unistd.h>
36#include "pnode.h"
37#include "internal.h"
38
39#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
40#define HASH_SIZE (1UL << HASH_SHIFT)
41
42static int event;
43static DEFINE_IDA(mnt_id_ida);
44static DEFINE_IDA(mnt_group_ida);
45static DEFINE_SPINLOCK(mnt_id_lock);
46static int mnt_id_start = 0;
47static int mnt_group_start = 1;
48
49static struct list_head *mount_hashtable __read_mostly;
50static struct kmem_cache *mnt_cache __read_mostly;
51static struct rw_semaphore namespace_sem;
52
53/* /sys/fs */
54struct kobject *fs_kobj;
55EXPORT_SYMBOL_GPL(fs_kobj);
56
57/*
58 * vfsmount lock may be taken for read to prevent changes to the
59 * vfsmount hash, ie. during mountpoint lookups or walking back
60 * up the tree.
61 *
62 * It should be taken for write in all cases where the vfsmount
63 * tree or hash is modified or when a vfsmount structure is modified.
64 */
65DEFINE_BRLOCK(vfsmount_lock);
66
67static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
68{
69    unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
70    tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
71    tmp = tmp + (tmp >> HASH_SHIFT);
72    return tmp & (HASH_SIZE - 1);
73}
74
75#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
76
77/*
78 * allocation is serialized by namespace_sem, but we need the spinlock to
79 * serialize with freeing.
80 */
81static int mnt_alloc_id(struct vfsmount *mnt)
82{
83    int res;
84
85retry:
86    ida_pre_get(&mnt_id_ida, GFP_KERNEL);
87    spin_lock(&mnt_id_lock);
88    res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
89    if (!res)
90        mnt_id_start = mnt->mnt_id + 1;
91    spin_unlock(&mnt_id_lock);
92    if (res == -EAGAIN)
93        goto retry;
94
95    return res;
96}
97
98static void mnt_free_id(struct vfsmount *mnt)
99{
100    int id = mnt->mnt_id;
101    spin_lock(&mnt_id_lock);
102    ida_remove(&mnt_id_ida, id);
103    if (mnt_id_start > id)
104        mnt_id_start = id;
105    spin_unlock(&mnt_id_lock);
106}
107
108/*
109 * Allocate a new peer group ID
110 *
111 * mnt_group_ida is protected by namespace_sem
112 */
113static int mnt_alloc_group_id(struct vfsmount *mnt)
114{
115    int res;
116
117    if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
118        return -ENOMEM;
119
120    res = ida_get_new_above(&mnt_group_ida,
121                mnt_group_start,
122                &mnt->mnt_group_id);
123    if (!res)
124        mnt_group_start = mnt->mnt_group_id + 1;
125
126    return res;
127}
128
129/*
130 * Release a peer group ID
131 */
132void mnt_release_group_id(struct vfsmount *mnt)
133{
134    int id = mnt->mnt_group_id;
135    ida_remove(&mnt_group_ida, id);
136    if (mnt_group_start > id)
137        mnt_group_start = id;
138    mnt->mnt_group_id = 0;
139}
140
141/*
142 * vfsmount lock must be held for read
143 */
144static inline void mnt_add_count(struct vfsmount *mnt, int n)
145{
146#ifdef CONFIG_SMP
147    this_cpu_add(mnt->mnt_pcp->mnt_count, n);
148#else
149    preempt_disable();
150    mnt->mnt_count += n;
151    preempt_enable();
152#endif
153}
154
155static inline void mnt_set_count(struct vfsmount *mnt, int n)
156{
157#ifdef CONFIG_SMP
158    this_cpu_write(mnt->mnt_pcp->mnt_count, n);
159#else
160    mnt->mnt_count = n;
161#endif
162}
163
164/*
165 * vfsmount lock must be held for read
166 */
167static inline void mnt_inc_count(struct vfsmount *mnt)
168{
169    mnt_add_count(mnt, 1);
170}
171
172/*
173 * vfsmount lock must be held for read
174 */
175static inline void mnt_dec_count(struct vfsmount *mnt)
176{
177    mnt_add_count(mnt, -1);
178}
179
180/*
181 * vfsmount lock must be held for write
182 */
183unsigned int mnt_get_count(struct vfsmount *mnt)
184{
185#ifdef CONFIG_SMP
186    unsigned int count = 0;
187    int cpu;
188
189    for_each_possible_cpu(cpu) {
190        count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
191    }
192
193    return count;
194#else
195    return mnt->mnt_count;
196#endif
197}
198
199static struct vfsmount *alloc_vfsmnt(const char *name)
200{
201    struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
202    if (mnt) {
203        int err;
204
205        err = mnt_alloc_id(mnt);
206        if (err)
207            goto out_free_cache;
208
209        if (name) {
210            mnt->mnt_devname = kstrdup(name, GFP_KERNEL);
211            if (!mnt->mnt_devname)
212                goto out_free_id;
213        }
214
215#ifdef CONFIG_SMP
216        mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
217        if (!mnt->mnt_pcp)
218            goto out_free_devname;
219
220        this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
221#else
222        mnt->mnt_count = 1;
223        mnt->mnt_writers = 0;
224#endif
225
226        INIT_LIST_HEAD(&mnt->mnt_hash);
227        INIT_LIST_HEAD(&mnt->mnt_child);
228        INIT_LIST_HEAD(&mnt->mnt_mounts);
229        INIT_LIST_HEAD(&mnt->mnt_list);
230        INIT_LIST_HEAD(&mnt->mnt_expire);
231        INIT_LIST_HEAD(&mnt->mnt_share);
232        INIT_LIST_HEAD(&mnt->mnt_slave_list);
233        INIT_LIST_HEAD(&mnt->mnt_slave);
234#ifdef CONFIG_FSNOTIFY
235        INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
236#endif
237    }
238    return mnt;
239
240#ifdef CONFIG_SMP
241out_free_devname:
242    kfree(mnt->mnt_devname);
243#endif
244out_free_id:
245    mnt_free_id(mnt);
246out_free_cache:
247    kmem_cache_free(mnt_cache, mnt);
248    return NULL;
249}
250
251/*
252 * Most r/o checks on a fs are for operations that take
253 * discrete amounts of time, like a write() or unlink().
254 * We must keep track of when those operations start
255 * (for permission checks) and when they end, so that
256 * we can determine when writes are able to occur to
257 * a filesystem.
258 */
259/*
260 * __mnt_is_readonly: check whether a mount is read-only
261 * @mnt: the mount to check for its write status
262 *
263 * This shouldn't be used directly ouside of the VFS.
264 * It does not guarantee that the filesystem will stay
265 * r/w, just that it is right *now*. This can not and
266 * should not be used in place of IS_RDONLY(inode).
267 * mnt_want/drop_write() will _keep_ the filesystem
268 * r/w.
269 */
270int __mnt_is_readonly(struct vfsmount *mnt)
271{
272    if (mnt->mnt_flags & MNT_READONLY)
273        return 1;
274    if (mnt->mnt_sb->s_flags & MS_RDONLY)
275        return 1;
276    return 0;
277}
278EXPORT_SYMBOL_GPL(__mnt_is_readonly);
279
280static inline void mnt_inc_writers(struct vfsmount *mnt)
281{
282#ifdef CONFIG_SMP
283    this_cpu_inc(mnt->mnt_pcp->mnt_writers);
284#else
285    mnt->mnt_writers++;
286#endif
287}
288
289static inline void mnt_dec_writers(struct vfsmount *mnt)
290{
291#ifdef CONFIG_SMP
292    this_cpu_dec(mnt->mnt_pcp->mnt_writers);
293#else
294    mnt->mnt_writers--;
295#endif
296}
297
298static unsigned int mnt_get_writers(struct vfsmount *mnt)
299{
300#ifdef CONFIG_SMP
301    unsigned int count = 0;
302    int cpu;
303
304    for_each_possible_cpu(cpu) {
305        count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
306    }
307
308    return count;
309#else
310    return mnt->mnt_writers;
311#endif
312}
313
314/*
315 * Most r/o checks on a fs are for operations that take
316 * discrete amounts of time, like a write() or unlink().
317 * We must keep track of when those operations start
318 * (for permission checks) and when they end, so that
319 * we can determine when writes are able to occur to
320 * a filesystem.
321 */
322/**
323 * mnt_want_write - get write access to a mount
324 * @mnt: the mount on which to take a write
325 *
326 * This tells the low-level filesystem that a write is
327 * about to be performed to it, and makes sure that
328 * writes are allowed before returning success. When
329 * the write operation is finished, mnt_drop_write()
330 * must be called. This is effectively a refcount.
331 */
332int mnt_want_write(struct vfsmount *mnt)
333{
334    int ret = 0;
335
336    preempt_disable();
337    mnt_inc_writers(mnt);
338    /*
339     * The store to mnt_inc_writers must be visible before we pass
340     * MNT_WRITE_HOLD loop below, so that the slowpath can see our
341     * incremented count after it has set MNT_WRITE_HOLD.
342     */
343    smp_mb();
344    while (mnt->mnt_flags & MNT_WRITE_HOLD)
345        cpu_relax();
346    /*
347     * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
348     * be set to match its requirements. So we must not load that until
349     * MNT_WRITE_HOLD is cleared.
350     */
351    smp_rmb();
352    if (__mnt_is_readonly(mnt)) {
353        mnt_dec_writers(mnt);
354        ret = -EROFS;
355        goto out;
356    }
357out:
358    preempt_enable();
359    return ret;
360}
361EXPORT_SYMBOL_GPL(mnt_want_write);
362
363/**
364 * mnt_clone_write - get write access to a mount
365 * @mnt: the mount on which to take a write
366 *
367 * This is effectively like mnt_want_write, except
368 * it must only be used to take an extra write reference
369 * on a mountpoint that we already know has a write reference
370 * on it. This allows some optimisation.
371 *
372 * After finished, mnt_drop_write must be called as usual to
373 * drop the reference.
374 */
375int mnt_clone_write(struct vfsmount *mnt)
376{
377    /* superblock may be r/o */
378    if (__mnt_is_readonly(mnt))
379        return -EROFS;
380    preempt_disable();
381    mnt_inc_writers(mnt);
382    preempt_enable();
383    return 0;
384}
385EXPORT_SYMBOL_GPL(mnt_clone_write);
386
387/**
388 * mnt_want_write_file - get write access to a file's mount
389 * @file: the file who's mount on which to take a write
390 *
391 * This is like mnt_want_write, but it takes a file and can
392 * do some optimisations if the file is open for write already
393 */
394int mnt_want_write_file(struct file *file)
395{
396    struct inode *inode = file->f_dentry->d_inode;
397    if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
398        return mnt_want_write(file->f_path.mnt);
399    else
400        return mnt_clone_write(file->f_path.mnt);
401}
402EXPORT_SYMBOL_GPL(mnt_want_write_file);
403
404/**
405 * mnt_drop_write - give up write access to a mount
406 * @mnt: the mount on which to give up write access
407 *
408 * Tells the low-level filesystem that we are done
409 * performing writes to it. Must be matched with
410 * mnt_want_write() call above.
411 */
412void mnt_drop_write(struct vfsmount *mnt)
413{
414    preempt_disable();
415    mnt_dec_writers(mnt);
416    preempt_enable();
417}
418EXPORT_SYMBOL_GPL(mnt_drop_write);
419
420static int mnt_make_readonly(struct vfsmount *mnt)
421{
422    int ret = 0;
423
424    br_write_lock(vfsmount_lock);
425    mnt->mnt_flags |= MNT_WRITE_HOLD;
426    /*
427     * After storing MNT_WRITE_HOLD, we'll read the counters. This store
428     * should be visible before we do.
429     */
430    smp_mb();
431
432    /*
433     * With writers on hold, if this value is zero, then there are
434     * definitely no active writers (although held writers may subsequently
435     * increment the count, they'll have to wait, and decrement it after
436     * seeing MNT_READONLY).
437     *
438     * It is OK to have counter incremented on one CPU and decremented on
439     * another: the sum will add up correctly. The danger would be when we
440     * sum up each counter, if we read a counter before it is incremented,
441     * but then read another CPU's count which it has been subsequently
442     * decremented from -- we would see more decrements than we should.
443     * MNT_WRITE_HOLD protects against this scenario, because
444     * mnt_want_write first increments count, then smp_mb, then spins on
445     * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
446     * we're counting up here.
447     */
448    if (mnt_get_writers(mnt) > 0)
449        ret = -EBUSY;
450    else
451        mnt->mnt_flags |= MNT_READONLY;
452    /*
453     * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
454     * that become unheld will see MNT_READONLY.
455     */
456    smp_wmb();
457    mnt->mnt_flags &= ~MNT_WRITE_HOLD;
458    br_write_unlock(vfsmount_lock);
459    return ret;
460}
461
462static void __mnt_unmake_readonly(struct vfsmount *mnt)
463{
464    br_write_lock(vfsmount_lock);
465    mnt->mnt_flags &= ~MNT_READONLY;
466    br_write_unlock(vfsmount_lock);
467}
468
469static void free_vfsmnt(struct vfsmount *mnt)
470{
471    kfree(mnt->mnt_devname);
472    mnt_free_id(mnt);
473#ifdef CONFIG_SMP
474    free_percpu(mnt->mnt_pcp);
475#endif
476    kmem_cache_free(mnt_cache, mnt);
477}
478
479/*
480 * find the first or last mount at @dentry on vfsmount @mnt depending on
481 * @dir. If @dir is set return the first mount else return the last mount.
482 * vfsmount_lock must be held for read or write.
483 */
484struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
485                  int dir)
486{
487    struct list_head *head = mount_hashtable + hash(mnt, dentry);
488    struct list_head *tmp = head;
489    struct vfsmount *p, *found = NULL;
490
491    for (;;) {
492        tmp = dir ? tmp->next : tmp->prev;
493        p = NULL;
494        if (tmp == head)
495            break;
496        p = list_entry(tmp, struct vfsmount, mnt_hash);
497        if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
498            found = p;
499            break;
500        }
501    }
502    return found;
503}
504
505/*
506 * lookup_mnt increments the ref count before returning
507 * the vfsmount struct.
508 */
509struct vfsmount *lookup_mnt(struct path *path)
510{
511    struct vfsmount *child_mnt;
512
513    br_read_lock(vfsmount_lock);
514    if ((child_mnt = __lookup_mnt(path->mnt, path->dentry, 1)))
515        mntget(child_mnt);
516    br_read_unlock(vfsmount_lock);
517    return child_mnt;
518}
519
520static inline int check_mnt(struct vfsmount *mnt)
521{
522    return mnt->mnt_ns == current->nsproxy->mnt_ns;
523}
524
525/*
526 * vfsmount lock must be held for write
527 */
528static void touch_mnt_namespace(struct mnt_namespace *ns)
529{
530    if (ns) {
531        ns->event = ++event;
532        wake_up_interruptible(&ns->poll);
533    }
534}
535
536/*
537 * vfsmount lock must be held for write
538 */
539static void __touch_mnt_namespace(struct mnt_namespace *ns)
540{
541    if (ns && ns->event != event) {
542        ns->event = event;
543        wake_up_interruptible(&ns->poll);
544    }
545}
546
547/*
548 * Clear dentry's mounted state if it has no remaining mounts.
549 * vfsmount_lock must be held for write.
550 */
551static void dentry_reset_mounted(struct vfsmount *mnt, struct dentry *dentry)
552{
553    unsigned u;
554
555    for (u = 0; u < HASH_SIZE; u++) {
556        struct vfsmount *p;
557
558        list_for_each_entry(p, &mount_hashtable[u], mnt_hash) {
559            if (p->mnt_mountpoint == dentry)
560                return;
561        }
562    }
563    spin_lock(&dentry->d_lock);
564    dentry->d_flags &= ~DCACHE_MOUNTED;
565    spin_unlock(&dentry->d_lock);
566}
567
568/*
569 * vfsmount lock must be held for write
570 */
571static void detach_mnt(struct vfsmount *mnt, struct path *old_path)
572{
573    old_path->dentry = mnt->mnt_mountpoint;
574    old_path->mnt = mnt->mnt_parent;
575    mnt->mnt_parent = mnt;
576    mnt->mnt_mountpoint = mnt->mnt_root;
577    list_del_init(&mnt->mnt_child);
578    list_del_init(&mnt->mnt_hash);
579    dentry_reset_mounted(old_path->mnt, old_path->dentry);
580}
581
582/*
583 * vfsmount lock must be held for write
584 */
585void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
586            struct vfsmount *child_mnt)
587{
588    child_mnt->mnt_parent = mntget(mnt);
589    child_mnt->mnt_mountpoint = dget(dentry);
590    spin_lock(&dentry->d_lock);
591    dentry->d_flags |= DCACHE_MOUNTED;
592    spin_unlock(&dentry->d_lock);
593}
594
595/*
596 * vfsmount lock must be held for write
597 */
598static void attach_mnt(struct vfsmount *mnt, struct path *path)
599{
600    mnt_set_mountpoint(path->mnt, path->dentry, mnt);
601    list_add_tail(&mnt->mnt_hash, mount_hashtable +
602            hash(path->mnt, path->dentry));
603    list_add_tail(&mnt->mnt_child, &path->mnt->mnt_mounts);
604}
605
606static inline void __mnt_make_longterm(struct vfsmount *mnt)
607{
608#ifdef CONFIG_SMP
609    atomic_inc(&mnt->mnt_longterm);
610#endif
611}
612
613/* needs vfsmount lock for write */
614static inline void __mnt_make_shortterm(struct vfsmount *mnt)
615{
616#ifdef CONFIG_SMP
617    atomic_dec(&mnt->mnt_longterm);
618#endif
619}
620
621/*
622 * vfsmount lock must be held for write
623 */
624static void commit_tree(struct vfsmount *mnt)
625{
626    struct vfsmount *parent = mnt->mnt_parent;
627    struct vfsmount *m;
628    LIST_HEAD(head);
629    struct mnt_namespace *n = parent->mnt_ns;
630
631    BUG_ON(parent == mnt);
632
633    list_add_tail(&head, &mnt->mnt_list);
634    list_for_each_entry(m, &head, mnt_list) {
635        m->mnt_ns = n;
636        __mnt_make_longterm(m);
637    }
638
639    list_splice(&head, n->list.prev);
640
641    list_add_tail(&mnt->mnt_hash, mount_hashtable +
642                hash(parent, mnt->mnt_mountpoint));
643    list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
644    touch_mnt_namespace(n);
645}
646
647static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
648{
649    struct list_head *next = p->mnt_mounts.next;
650    if (next == &p->mnt_mounts) {
651        while (1) {
652            if (p == root)
653                return NULL;
654            next = p->mnt_child.next;
655            if (next != &p->mnt_parent->mnt_mounts)
656                break;
657            p = p->mnt_parent;
658        }
659    }
660    return list_entry(next, struct vfsmount, mnt_child);
661}
662
663static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
664{
665    struct list_head *prev = p->mnt_mounts.prev;
666    while (prev != &p->mnt_mounts) {
667        p = list_entry(prev, struct vfsmount, mnt_child);
668        prev = p->mnt_mounts.prev;
669    }
670    return p;
671}
672
673struct vfsmount *
674vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
675{
676    struct vfsmount *mnt;
677    struct dentry *root;
678
679    if (!type)
680        return ERR_PTR(-ENODEV);
681
682    mnt = alloc_vfsmnt(name);
683    if (!mnt)
684        return ERR_PTR(-ENOMEM);
685
686    if (flags & MS_KERNMOUNT)
687        mnt->mnt_flags = MNT_INTERNAL;
688
689    root = mount_fs(type, flags, name, data);
690    if (IS_ERR(root)) {
691        free_vfsmnt(mnt);
692        return ERR_CAST(root);
693    }
694
695    mnt->mnt_root = root;
696    mnt->mnt_sb = root->d_sb;
697    mnt->mnt_mountpoint = mnt->mnt_root;
698    mnt->mnt_parent = mnt;
699    return mnt;
700}
701EXPORT_SYMBOL_GPL(vfs_kern_mount);
702
703static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
704                    int flag)
705{
706    struct super_block *sb = old->mnt_sb;
707    struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
708
709    if (mnt) {
710        if (flag & (CL_SLAVE | CL_PRIVATE))
711            mnt->mnt_group_id = 0; /* not a peer of original */
712        else
713            mnt->mnt_group_id = old->mnt_group_id;
714
715        if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
716            int err = mnt_alloc_group_id(mnt);
717            if (err)
718                goto out_free;
719        }
720
721        mnt->mnt_flags = old->mnt_flags & ~MNT_WRITE_HOLD;
722        atomic_inc(&sb->s_active);
723        mnt->mnt_sb = sb;
724        mnt->mnt_root = dget(root);
725        mnt->mnt_mountpoint = mnt->mnt_root;
726        mnt->mnt_parent = mnt;
727
728        if (flag & CL_SLAVE) {
729            list_add(&mnt->mnt_slave, &old->mnt_slave_list);
730            mnt->mnt_master = old;
731            CLEAR_MNT_SHARED(mnt);
732        } else if (!(flag & CL_PRIVATE)) {
733            if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
734                list_add(&mnt->mnt_share, &old->mnt_share);
735            if (IS_MNT_SLAVE(old))
736                list_add(&mnt->mnt_slave, &old->mnt_slave);
737            mnt->mnt_master = old->mnt_master;
738        }
739        if (flag & CL_MAKE_SHARED)
740            set_mnt_shared(mnt);
741
742        /* stick the duplicate mount on the same expiry list
743         * as the original if that was on one */
744        if (flag & CL_EXPIRE) {
745            if (!list_empty(&old->mnt_expire))
746                list_add(&mnt->mnt_expire, &old->mnt_expire);
747        }
748    }
749    return mnt;
750
751 out_free:
752    free_vfsmnt(mnt);
753    return NULL;
754}
755
756static inline void mntfree(struct vfsmount *mnt)
757{
758    struct super_block *sb = mnt->mnt_sb;
759
760    /*
761     * This probably indicates that somebody messed
762     * up a mnt_want/drop_write() pair. If this
763     * happens, the filesystem was probably unable
764     * to make r/w->r/o transitions.
765     */
766    /*
767     * The locking used to deal with mnt_count decrement provides barriers,
768     * so mnt_get_writers() below is safe.
769     */
770    WARN_ON(mnt_get_writers(mnt));
771    fsnotify_vfsmount_delete(mnt);
772    dput(mnt->mnt_root);
773    free_vfsmnt(mnt);
774    deactivate_super(sb);
775}
776
777static void mntput_no_expire(struct vfsmount *mnt)
778{
779put_again:
780#ifdef CONFIG_SMP
781    br_read_lock(vfsmount_lock);
782    if (likely(atomic_read(&mnt->mnt_longterm))) {
783        mnt_dec_count(mnt);
784        br_read_unlock(vfsmount_lock);
785        return;
786    }
787    br_read_unlock(vfsmount_lock);
788
789    br_write_lock(vfsmount_lock);
790    mnt_dec_count(mnt);
791    if (mnt_get_count(mnt)) {
792        br_write_unlock(vfsmount_lock);
793        return;
794    }
795#else
796    mnt_dec_count(mnt);
797    if (likely(mnt_get_count(mnt)))
798        return;
799    br_write_lock(vfsmount_lock);
800#endif
801    if (unlikely(mnt->mnt_pinned)) {
802        mnt_add_count(mnt, mnt->mnt_pinned + 1);
803        mnt->mnt_pinned = 0;
804        br_write_unlock(vfsmount_lock);
805        acct_auto_close_mnt(mnt);
806        goto put_again;
807    }
808    br_write_unlock(vfsmount_lock);
809    mntfree(mnt);
810}
811
812void mntput(struct vfsmount *mnt)
813{
814    if (mnt) {
815        /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
816        if (unlikely(mnt->mnt_expiry_mark))
817            mnt->mnt_expiry_mark = 0;
818        mntput_no_expire(mnt);
819    }
820}
821EXPORT_SYMBOL(mntput);
822
823struct vfsmount *mntget(struct vfsmount *mnt)
824{
825    if (mnt)
826        mnt_inc_count(mnt);
827    return mnt;
828}
829EXPORT_SYMBOL(mntget);
830
831void mnt_pin(struct vfsmount *mnt)
832{
833    br_write_lock(vfsmount_lock);
834    mnt->mnt_pinned++;
835    br_write_unlock(vfsmount_lock);
836}
837EXPORT_SYMBOL(mnt_pin);
838
839void mnt_unpin(struct vfsmount *mnt)
840{
841    br_write_lock(vfsmount_lock);
842    if (mnt->mnt_pinned) {
843        mnt_inc_count(mnt);
844        mnt->mnt_pinned--;
845    }
846    br_write_unlock(vfsmount_lock);
847}
848EXPORT_SYMBOL(mnt_unpin);
849
850static inline void mangle(struct seq_file *m, const char *s)
851{
852    seq_escape(m, s, " \t\n\\");
853}
854
855/*
856 * Simple .show_options callback for filesystems which don't want to
857 * implement more complex mount option showing.
858 *
859 * See also save_mount_options().
860 */
861int generic_show_options(struct seq_file *m, struct vfsmount *mnt)
862{
863    const char *options;
864
865    rcu_read_lock();
866    options = rcu_dereference(mnt->mnt_sb->s_options);
867
868    if (options != NULL && options[0]) {
869        seq_putc(m, ',');
870        mangle(m, options);
871    }
872    rcu_read_unlock();
873
874    return 0;
875}
876EXPORT_SYMBOL(generic_show_options);
877
878/*
879 * If filesystem uses generic_show_options(), this function should be
880 * called from the fill_super() callback.
881 *
882 * The .remount_fs callback usually needs to be handled in a special
883 * way, to make sure, that previous options are not overwritten if the
884 * remount fails.
885 *
886 * Also note, that if the filesystem's .remount_fs function doesn't
887 * reset all options to their default value, but changes only newly
888 * given options, then the displayed options will not reflect reality
889 * any more.
890 */
891void save_mount_options(struct super_block *sb, char *options)
892{
893    BUG_ON(sb->s_options);
894    rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
895}
896EXPORT_SYMBOL(save_mount_options);
897
898void replace_mount_options(struct super_block *sb, char *options)
899{
900    char *old = sb->s_options;
901    rcu_assign_pointer(sb->s_options, options);
902    if (old) {
903        synchronize_rcu();
904        kfree(old);
905    }
906}
907EXPORT_SYMBOL(replace_mount_options);
908
909#ifdef CONFIG_PROC_FS
910/* iterator */
911static void *m_start(struct seq_file *m, loff_t *pos)
912{
913    struct proc_mounts *p = m->private;
914
915    down_read(&namespace_sem);
916    return seq_list_start(&p->ns->list, *pos);
917}
918
919static void *m_next(struct seq_file *m, void *v, loff_t *pos)
920{
921    struct proc_mounts *p = m->private;
922
923    return seq_list_next(v, &p->ns->list, pos);
924}
925
926static void m_stop(struct seq_file *m, void *v)
927{
928    up_read(&namespace_sem);
929}
930
931int mnt_had_events(struct proc_mounts *p)
932{
933    struct mnt_namespace *ns = p->ns;
934    int res = 0;
935
936    br_read_lock(vfsmount_lock);
937    if (p->m.poll_event != ns->event) {
938        p->m.poll_event = ns->event;
939        res = 1;
940    }
941    br_read_unlock(vfsmount_lock);
942
943    return res;
944}
945
946struct proc_fs_info {
947    int flag;
948    const char *str;
949};
950
951static int show_sb_opts(struct seq_file *m, struct super_block *sb)
952{
953    static const struct proc_fs_info fs_info[] = {
954        { MS_SYNCHRONOUS, ",sync" },
955        { MS_DIRSYNC, ",dirsync" },
956        { MS_MANDLOCK, ",mand" },
957        { 0, NULL }
958    };
959    const struct proc_fs_info *fs_infop;
960
961    for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
962        if (sb->s_flags & fs_infop->flag)
963            seq_puts(m, fs_infop->str);
964    }
965
966    return security_sb_show_options(m, sb);
967}
968
969static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
970{
971    static const struct proc_fs_info mnt_info[] = {
972        { MNT_NOSUID, ",nosuid" },
973        { MNT_NODEV, ",nodev" },
974        { MNT_NOEXEC, ",noexec" },
975        { MNT_NOATIME, ",noatime" },
976        { MNT_NODIRATIME, ",nodiratime" },
977        { MNT_RELATIME, ",relatime" },
978        { 0, NULL }
979    };
980    const struct proc_fs_info *fs_infop;
981
982    for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
983        if (mnt->mnt_flags & fs_infop->flag)
984            seq_puts(m, fs_infop->str);
985    }
986}
987
988static void show_type(struct seq_file *m, struct super_block *sb)
989{
990    mangle(m, sb->s_type->name);
991    if (sb->s_subtype && sb->s_subtype[0]) {
992        seq_putc(m, '.');
993        mangle(m, sb->s_subtype);
994    }
995}
996
997static int show_vfsmnt(struct seq_file *m, void *v)
998{
999    struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1000    int err = 0;
1001    struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1002
1003    if (mnt->mnt_sb->s_op->show_devname) {
1004        err = mnt->mnt_sb->s_op->show_devname(m, mnt);
1005        if (err)
1006            goto out;
1007    } else {
1008        mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
1009    }
1010    seq_putc(m, ' ');
1011    seq_path(m, &mnt_path, " \t\n\\");
1012    seq_putc(m, ' ');
1013    show_type(m, mnt->mnt_sb);
1014    seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
1015    err = show_sb_opts(m, mnt->mnt_sb);
1016    if (err)
1017        goto out;
1018    show_mnt_opts(m, mnt);
1019    if (mnt->mnt_sb->s_op->show_options)
1020        err = mnt->mnt_sb->s_op->show_options(m, mnt);
1021    seq_puts(m, " 0 0\n");
1022out:
1023    return err;
1024}
1025
1026const struct seq_operations mounts_op = {
1027    .start = m_start,
1028    .next = m_next,
1029    .stop = m_stop,
1030    .show = show_vfsmnt
1031};
1032
1033static int show_mountinfo(struct seq_file *m, void *v)
1034{
1035    struct proc_mounts *p = m->private;
1036    struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1037    struct super_block *sb = mnt->mnt_sb;
1038    struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1039    struct path root = p->root;
1040    int err = 0;
1041
1042    seq_printf(m, "%i %i %u:%u ", mnt->mnt_id, mnt->mnt_parent->mnt_id,
1043           MAJOR(sb->s_dev), MINOR(sb->s_dev));
1044    if (sb->s_op->show_path)
1045        err = sb->s_op->show_path(m, mnt);
1046    else
1047        seq_dentry(m, mnt->mnt_root, " \t\n\\");
1048    if (err)
1049        goto out;
1050    seq_putc(m, ' ');
1051
1052    /* mountpoints outside of chroot jail will give SEQ_SKIP on this */
1053    err = seq_path_root(m, &mnt_path, &root, " \t\n\\");
1054    if (err)
1055        goto out;
1056
1057    seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
1058    show_mnt_opts(m, mnt);
1059
1060    /* Tagged fields ("foo:X" or "bar") */
1061    if (IS_MNT_SHARED(mnt))
1062        seq_printf(m, " shared:%i", mnt->mnt_group_id);
1063    if (IS_MNT_SLAVE(mnt)) {
1064        int master = mnt->mnt_master->mnt_group_id;
1065        int dom = get_dominating_id(mnt, &p->root);
1066        seq_printf(m, " master:%i", master);
1067        if (dom && dom != master)
1068            seq_printf(m, " propagate_from:%i", dom);
1069    }
1070    if (IS_MNT_UNBINDABLE(mnt))
1071        seq_puts(m, " unbindable");
1072
1073    /* Filesystem specific data */
1074    seq_puts(m, " - ");
1075    show_type(m, sb);
1076    seq_putc(m, ' ');
1077    if (sb->s_op->show_devname)
1078        err = sb->s_op->show_devname(m, mnt);
1079    else
1080        mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
1081    if (err)
1082        goto out;
1083    seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
1084    err = show_sb_opts(m, sb);
1085    if (err)
1086        goto out;
1087    if (sb->s_op->show_options)
1088        err = sb->s_op->show_options(m, mnt);
1089    seq_putc(m, '\n');
1090out:
1091    return err;
1092}
1093
1094const struct seq_operations mountinfo_op = {
1095    .start = m_start,
1096    .next = m_next,
1097    .stop = m_stop,
1098    .show = show_mountinfo,
1099};
1100
1101static int show_vfsstat(struct seq_file *m, void *v)
1102{
1103    struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1104    struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1105    int err = 0;
1106
1107    /* device */
1108    if (mnt->mnt_sb->s_op->show_devname) {
1109        seq_puts(m, "device ");
1110        err = mnt->mnt_sb->s_op->show_devname(m, mnt);
1111    } else {
1112        if (mnt->mnt_devname) {
1113            seq_puts(m, "device ");
1114            mangle(m, mnt->mnt_devname);
1115        } else
1116            seq_puts(m, "no device");
1117    }
1118
1119    /* mount point */
1120    seq_puts(m, " mounted on ");
1121    seq_path(m, &mnt_path, " \t\n\\");
1122    seq_putc(m, ' ');
1123
1124    /* file system type */
1125    seq_puts(m, "with fstype ");
1126    show_type(m, mnt->mnt_sb);
1127
1128    /* optional statistics */
1129    if (mnt->mnt_sb->s_op->show_stats) {
1130        seq_putc(m, ' ');
1131        if (!err)
1132            err = mnt->mnt_sb->s_op->show_stats(m, mnt);
1133    }
1134
1135    seq_putc(m, '\n');
1136    return err;
1137}
1138
1139const struct seq_operations mountstats_op = {
1140    .start = m_start,
1141    .next = m_next,
1142    .stop = m_stop,
1143    .show = show_vfsstat,
1144};
1145#endif /* CONFIG_PROC_FS */
1146
1147/**
1148 * may_umount_tree - check if a mount tree is busy
1149 * @mnt: root of mount tree
1150 *
1151 * This is called to check if a tree of mounts has any
1152 * open files, pwds, chroots or sub mounts that are
1153 * busy.
1154 */
1155int may_umount_tree(struct vfsmount *mnt)
1156{
1157    int actual_refs = 0;
1158    int minimum_refs = 0;
1159    struct vfsmount *p;
1160
1161    /* write lock needed for mnt_get_count */
1162    br_write_lock(vfsmount_lock);
1163    for (p = mnt; p; p = next_mnt(p, mnt)) {
1164        actual_refs += mnt_get_count(p);
1165        minimum_refs += 2;
1166    }
1167    br_write_unlock(vfsmount_lock);
1168
1169    if (actual_refs > minimum_refs)
1170        return 0;
1171
1172    return 1;
1173}
1174
1175EXPORT_SYMBOL(may_umount_tree);
1176
1177/**
1178 * may_umount - check if a mount point is busy
1179 * @mnt: root of mount
1180 *
1181 * This is called to check if a mount point has any
1182 * open files, pwds, chroots or sub mounts. If the
1183 * mount has sub mounts this will return busy
1184 * regardless of whether the sub mounts are busy.
1185 *
1186 * Doesn't take quota and stuff into account. IOW, in some cases it will
1187 * give false negatives. The main reason why it's here is that we need
1188 * a non-destructive way to look for easily umountable filesystems.
1189 */
1190int may_umount(struct vfsmount *mnt)
1191{
1192    int ret = 1;
1193    down_read(&namespace_sem);
1194    br_write_lock(vfsmount_lock);
1195    if (propagate_mount_busy(mnt, 2))
1196        ret = 0;
1197    br_write_unlock(vfsmount_lock);
1198    up_read(&namespace_sem);
1199    return ret;
1200}
1201
1202EXPORT_SYMBOL(may_umount);
1203
1204void release_mounts(struct list_head *head)
1205{
1206    struct vfsmount *mnt;
1207    while (!list_empty(head)) {
1208        mnt = list_first_entry(head, struct vfsmount, mnt_hash);
1209        list_del_init(&mnt->mnt_hash);
1210        if (mnt->mnt_parent != mnt) {
1211            struct dentry *dentry;
1212            struct vfsmount *m;
1213
1214            br_write_lock(vfsmount_lock);
1215            dentry = mnt->mnt_mountpoint;
1216            m = mnt->mnt_parent;
1217            mnt->mnt_mountpoint = mnt->mnt_root;
1218            mnt->mnt_parent = mnt;
1219            m->mnt_ghosts--;
1220            br_write_unlock(vfsmount_lock);
1221            dput(dentry);
1222            mntput(m);
1223        }
1224        mntput(mnt);
1225    }
1226}
1227
1228/*
1229 * vfsmount lock must be held for write
1230 * namespace_sem must be held for write
1231 */
1232void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
1233{
1234    LIST_HEAD(tmp_list);
1235    struct vfsmount *p;
1236
1237    for (p = mnt; p; p = next_mnt(p, mnt))
1238        list_move(&p->mnt_hash, &tmp_list);
1239
1240    if (propagate)
1241        propagate_umount(&tmp_list);
1242
1243    list_for_each_entry(p, &tmp_list, mnt_hash) {
1244        list_del_init(&p->mnt_expire);
1245        list_del_init(&p->mnt_list);
1246        __touch_mnt_namespace(p->mnt_ns);
1247        p->mnt_ns = NULL;
1248        __mnt_make_shortterm(p);
1249        list_del_init(&p->mnt_child);
1250        if (p->mnt_parent != p) {
1251            p->mnt_parent->mnt_ghosts++;
1252            dentry_reset_mounted(p->mnt_parent, p->mnt_mountpoint);
1253        }
1254        change_mnt_propagation(p, MS_PRIVATE);
1255    }
1256    list_splice(&tmp_list, kill);
1257}
1258
1259static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts);
1260
1261static int do_umount(struct vfsmount *mnt, int flags)
1262{
1263    struct super_block *sb = mnt->mnt_sb;
1264    int retval;
1265    LIST_HEAD(umount_list);
1266
1267    retval = security_sb_umount(mnt, flags);
1268    if (retval)
1269        return retval;
1270
1271    /*
1272     * Allow userspace to request a mountpoint be expired rather than
1273     * unmounting unconditionally. Unmount only happens if:
1274     * (1) the mark is already set (the mark is cleared by mntput())
1275     * (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1276     */
1277    if (flags & MNT_EXPIRE) {
1278        if (mnt == current->fs->root.mnt ||
1279            flags & (MNT_FORCE | MNT_DETACH))
1280            return -EINVAL;
1281
1282        /*
1283         * probably don't strictly need the lock here if we examined
1284         * all race cases, but it's a slowpath.
1285         */
1286        br_write_lock(vfsmount_lock);
1287        if (mnt_get_count(mnt) != 2) {
1288            br_write_unlock(vfsmount_lock);
1289            return -EBUSY;
1290        }
1291        br_write_unlock(vfsmount_lock);
1292
1293        if (!xchg(&mnt->mnt_expiry_mark, 1))
1294            return -EAGAIN;
1295    }
1296
1297    /*
1298     * If we may have to abort operations to get out of this
1299     * mount, and they will themselves hold resources we must
1300     * allow the fs to do things. In the Unix tradition of
1301     * 'Gee thats tricky lets do it in userspace' the umount_begin
1302     * might fail to complete on the first run through as other tasks
1303     * must return, and the like. Thats for the mount program to worry
1304     * about for the moment.
1305     */
1306
1307    if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1308        sb->s_op->umount_begin(sb);
1309    }
1310
1311    /*
1312     * No sense to grab the lock for this test, but test itself looks
1313     * somewhat bogus. Suggestions for better replacement?
1314     * Ho-hum... In principle, we might treat that as umount + switch
1315     * to rootfs. GC would eventually take care of the old vfsmount.
1316     * Actually it makes sense, especially if rootfs would contain a
1317     * /reboot - static binary that would close all descriptors and
1318     * call reboot(9). Then init(8) could umount root and exec /reboot.
1319     */
1320    if (mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1321        /*
1322         * Special case for "unmounting" root ...
1323         * we just try to remount it readonly.
1324         */
1325        down_write(&sb->s_umount);
1326        if (!(sb->s_flags & MS_RDONLY))
1327            retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1328        up_write(&sb->s_umount);
1329        return retval;
1330    }
1331
1332    down_write(&namespace_sem);
1333    br_write_lock(vfsmount_lock);
1334    event++;
1335
1336    if (!(flags & MNT_DETACH))
1337        shrink_submounts(mnt, &umount_list);
1338
1339    retval = -EBUSY;
1340    if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
1341        if (!list_empty(&mnt->mnt_list))
1342            umount_tree(mnt, 1, &umount_list);
1343        retval = 0;
1344    }
1345    br_write_unlock(vfsmount_lock);
1346    up_write(&namespace_sem);
1347    release_mounts(&umount_list);
1348    return retval;
1349}
1350
1351/*
1352 * Now umount can handle mount points as well as block devices.
1353 * This is important for filesystems which use unnamed block devices.
1354 *
1355 * We now support a flag for forced unmount like the other 'big iron'
1356 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1357 */
1358
1359SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1360{
1361    struct path path;
1362    int retval;
1363    int lookup_flags = 0;
1364
1365    if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1366        return -EINVAL;
1367
1368    if (!(flags & UMOUNT_NOFOLLOW))
1369        lookup_flags |= LOOKUP_FOLLOW;
1370
1371    retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
1372    if (retval)
1373        goto out;
1374    retval = -EINVAL;
1375    if (path.dentry != path.mnt->mnt_root)
1376        goto dput_and_out;
1377    if (!check_mnt(path.mnt))
1378        goto dput_and_out;
1379
1380    retval = -EPERM;
1381    if (!capable(CAP_SYS_ADMIN))
1382        goto dput_and_out;
1383
1384    retval = do_umount(path.mnt, flags);
1385dput_and_out:
1386    /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1387    dput(path.dentry);
1388    mntput_no_expire(path.mnt);
1389out:
1390    return retval;
1391}
1392
1393#ifdef __ARCH_WANT_SYS_OLDUMOUNT
1394
1395/*
1396 * The 2.0 compatible umount. No flags.
1397 */
1398SYSCALL_DEFINE1(oldumount, char __user *, name)
1399{
1400    return sys_umount(name, 0);
1401}
1402
1403#endif
1404
1405static int mount_is_safe(struct path *path)
1406{
1407    if (capable(CAP_SYS_ADMIN))
1408        return 0;
1409    return -EPERM;
1410#ifdef notyet
1411    if (S_ISLNK(path->dentry->d_inode->i_mode))
1412        return -EPERM;
1413    if (path->dentry->d_inode->i_mode & S_ISVTX) {
1414        if (current_uid() != path->dentry->d_inode->i_uid)
1415            return -EPERM;
1416    }
1417    if (inode_permission(path->dentry->d_inode, MAY_WRITE))
1418        return -EPERM;
1419    return 0;
1420#endif
1421}
1422
1423struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
1424                    int flag)
1425{
1426    struct vfsmount *res, *p, *q, *r, *s;
1427    struct path path;
1428
1429    if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
1430        return NULL;
1431
1432    res = q = clone_mnt(mnt, dentry, flag);
1433    if (!q)
1434        goto Enomem;
1435    q->mnt_mountpoint = mnt->mnt_mountpoint;
1436
1437    p = mnt;
1438    list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1439        if (!is_subdir(r->mnt_mountpoint, dentry))
1440            continue;
1441
1442        for (s = r; s; s = next_mnt(s, r)) {
1443            if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
1444                s = skip_mnt_tree(s);
1445                continue;
1446            }
1447            while (p != s->mnt_parent) {
1448                p = p->mnt_parent;
1449                q = q->mnt_parent;
1450            }
1451            p = s;
1452            path.mnt = q;
1453            path.dentry = p->mnt_mountpoint;
1454            q = clone_mnt(p, p->mnt_root, flag);
1455            if (!q)
1456                goto Enomem;
1457            br_write_lock(vfsmount_lock);
1458            list_add_tail(&q->mnt_list, &res->mnt_list);
1459            attach_mnt(q, &path);
1460            br_write_unlock(vfsmount_lock);
1461        }
1462    }
1463    return res;
1464Enomem:
1465    if (res) {
1466        LIST_HEAD(umount_list);
1467        br_write_lock(vfsmount_lock);
1468        umount_tree(res, 0, &umount_list);
1469        br_write_unlock(vfsmount_lock);
1470        release_mounts(&umount_list);
1471    }
1472    return NULL;
1473}
1474
1475struct vfsmount *collect_mounts(struct path *path)
1476{
1477    struct vfsmount *tree;
1478    down_write(&namespace_sem);
1479    tree = copy_tree(path->mnt, path->dentry, CL_COPY_ALL | CL_PRIVATE);
1480    up_write(&namespace_sem);
1481    return tree;
1482}
1483
1484void drop_collected_mounts(struct vfsmount *mnt)
1485{
1486    LIST_HEAD(umount_list);
1487    down_write(&namespace_sem);
1488    br_write_lock(vfsmount_lock);
1489    umount_tree(mnt, 0, &umount_list);
1490    br_write_unlock(vfsmount_lock);
1491    up_write(&namespace_sem);
1492    release_mounts(&umount_list);
1493}
1494
1495int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1496           struct vfsmount *root)
1497{
1498    struct vfsmount *mnt;
1499    int res = f(root, arg);
1500    if (res)
1501        return res;
1502    list_for_each_entry(mnt, &root->mnt_list, mnt_list) {
1503        res = f(mnt, arg);
1504        if (res)
1505            return res;
1506    }
1507    return 0;
1508}
1509
1510static void cleanup_group_ids(struct vfsmount *mnt, struct vfsmount *end)
1511{
1512    struct vfsmount *p;
1513
1514    for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1515        if (p->mnt_group_id && !IS_MNT_SHARED(p))
1516            mnt_release_group_id(p);
1517    }
1518}
1519
1520static int invent_group_ids(struct vfsmount *mnt, bool recurse)
1521{
1522    struct vfsmount *p;
1523
1524    for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1525        if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1526            int err = mnt_alloc_group_id(p);
1527            if (err) {
1528                cleanup_group_ids(mnt, p);
1529                return err;
1530            }
1531        }
1532    }
1533
1534    return 0;
1535}
1536
1537/*
1538 * @source_mnt : mount tree to be attached
1539 * @nd : place the mount tree @source_mnt is attached
1540 * @parent_nd : if non-null, detach the source_mnt from its parent and
1541 * store the parent mount and mountpoint dentry.
1542 * (done when source_mnt is moved)
1543 *
1544 * NOTE: in the table below explains the semantics when a source mount
1545 * of a given type is attached to a destination mount of a given type.
1546 * ---------------------------------------------------------------------------
1547 * | BIND MOUNT OPERATION |
1548 * |**************************************************************************
1549 * | source-->| shared | private | slave | unbindable |
1550 * | dest | | | | |
1551 * | | | | | | |
1552 * | v | | | | |
1553 * |**************************************************************************
1554 * | shared | shared (++) | shared (+) | shared(+++)| invalid |
1555 * | | | | | |
1556 * |non-shared| shared (+) | private | slave (*) | invalid |
1557 * ***************************************************************************
1558 * A bind operation clones the source mount and mounts the clone on the
1559 * destination mount.
1560 *
1561 * (++) the cloned mount is propagated to all the mounts in the propagation
1562 * tree of the destination mount and the cloned mount is added to
1563 * the peer group of the source mount.
1564 * (+) the cloned mount is created under the destination mount and is marked
1565 * as shared. The cloned mount is added to the peer group of the source
1566 * mount.
1567 * (+++) the mount is propagated to all the mounts in the propagation tree
1568 * of the destination mount and the cloned mount is made slave
1569 * of the same master as that of the source mount. The cloned mount
1570 * is marked as 'shared and slave'.
1571 * (*) the cloned mount is made a slave of the same master as that of the
1572 * source mount.
1573 *
1574 * ---------------------------------------------------------------------------
1575 * | MOVE MOUNT OPERATION |
1576 * |**************************************************************************
1577 * | source-->| shared | private | slave | unbindable |
1578 * | dest | | | | |
1579 * | | | | | | |
1580 * | v | | | | |
1581 * |**************************************************************************
1582 * | shared | shared (+) | shared (+) | shared(+++) | invalid |
1583 * | | | | | |
1584 * |non-shared| shared (+*) | private | slave (*) | unbindable |
1585 * ***************************************************************************
1586 *
1587 * (+) the mount is moved to the destination. And is then propagated to
1588 * all the mounts in the propagation tree of the destination mount.
1589 * (+*) the mount is moved to the destination.
1590 * (+++) the mount is moved to the destination and is then propagated to
1591 * all the mounts belonging to the destination mount's propagation tree.
1592 * the mount is marked as 'shared and slave'.
1593 * (*) the mount continues to be a slave at the new location.
1594 *
1595 * if the source mount is a tree, the operations explained above is
1596 * applied to each mount in the tree.
1597 * Must be called without spinlocks held, since this function can sleep
1598 * in allocations.
1599 */
1600static int attach_recursive_mnt(struct vfsmount *source_mnt,
1601            struct path *path, struct path *parent_path)
1602{
1603    LIST_HEAD(tree_list);
1604    struct vfsmount *dest_mnt = path->mnt;
1605    struct dentry *dest_dentry = path->dentry;
1606    struct vfsmount *child, *p;
1607    int err;
1608
1609    if (IS_MNT_SHARED(dest_mnt)) {
1610        err = invent_group_ids(source_mnt, true);
1611        if (err)
1612            goto out;
1613    }
1614    err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list);
1615    if (err)
1616        goto out_cleanup_ids;
1617
1618    br_write_lock(vfsmount_lock);
1619
1620    if (IS_MNT_SHARED(dest_mnt)) {
1621        for (p = source_mnt; p; p = next_mnt(p, source_mnt))
1622            set_mnt_shared(p);
1623    }
1624    if (parent_path) {
1625        detach_mnt(source_mnt, parent_path);
1626        attach_mnt(source_mnt, path);
1627        touch_mnt_namespace(parent_path->mnt->mnt_ns);
1628    } else {
1629        mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
1630        commit_tree(source_mnt);
1631    }
1632
1633    list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
1634        list_del_init(&child->mnt_hash);
1635        commit_tree(child);
1636    }
1637    br_write_unlock(vfsmount_lock);
1638
1639    return 0;
1640
1641 out_cleanup_ids:
1642    if (IS_MNT_SHARED(dest_mnt))
1643        cleanup_group_ids(source_mnt, NULL);
1644 out:
1645    return err;
1646}
1647
1648static int lock_mount(struct path *path)
1649{
1650    struct vfsmount *mnt;
1651retry:
1652    mutex_lock(&path->dentry->d_inode->i_mutex);
1653    if (unlikely(cant_mount(path->dentry))) {
1654        mutex_unlock(&path->dentry->d_inode->i_mutex);
1655        return -ENOENT;
1656    }
1657    down_write(&namespace_sem);
1658    mnt = lookup_mnt(path);
1659    if (likely(!mnt))
1660        return 0;
1661    up_write(&namespace_sem);
1662    mutex_unlock(&path->dentry->d_inode->i_mutex);
1663    path_put(path);
1664    path->mnt = mnt;
1665    path->dentry = dget(mnt->mnt_root);
1666    goto retry;
1667}
1668
1669static void unlock_mount(struct path *path)
1670{
1671    up_write(&namespace_sem);
1672    mutex_unlock(&path->dentry->d_inode->i_mutex);
1673}
1674
1675static int graft_tree(struct vfsmount *mnt, struct path *path)
1676{
1677    if (mnt->mnt_sb->s_flags & MS_NOUSER)
1678        return -EINVAL;
1679
1680    if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1681          S_ISDIR(mnt->mnt_root->d_inode->i_mode))
1682        return -ENOTDIR;
1683
1684    if (d_unlinked(path->dentry))
1685        return -ENOENT;
1686
1687    return attach_recursive_mnt(mnt, path, NULL);
1688}
1689
1690/*
1691 * Sanity check the flags to change_mnt_propagation.
1692 */
1693
1694static int flags_to_propagation_type(int flags)
1695{
1696    int type = flags & ~(MS_REC | MS_SILENT);
1697
1698    /* Fail if any non-propagation flags are set */
1699    if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1700        return 0;
1701    /* Only one propagation flag should be set */
1702    if (!is_power_of_2(type))
1703        return 0;
1704    return type;
1705}
1706
1707/*
1708 * recursively change the type of the mountpoint.
1709 */
1710static int do_change_type(struct path *path, int flag)
1711{
1712    struct vfsmount *m, *mnt = path->mnt;
1713    int recurse = flag & MS_REC;
1714    int type;
1715    int err = 0;
1716
1717    if (!capable(CAP_SYS_ADMIN))
1718        return -EPERM;
1719
1720    if (path->dentry != path->mnt->mnt_root)
1721        return -EINVAL;
1722
1723    type = flags_to_propagation_type(flag);
1724    if (!type)
1725        return -EINVAL;
1726
1727    down_write(&namespace_sem);
1728    if (type == MS_SHARED) {
1729        err = invent_group_ids(mnt, recurse);
1730        if (err)
1731            goto out_unlock;
1732    }
1733
1734    br_write_lock(vfsmount_lock);
1735    for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
1736        change_mnt_propagation(m, type);
1737    br_write_unlock(vfsmount_lock);
1738
1739 out_unlock:
1740    up_write(&namespace_sem);
1741    return err;
1742}
1743
1744/*
1745 * do loopback mount.
1746 */
1747static int do_loopback(struct path *path, char *old_name,
1748                int recurse)
1749{
1750    LIST_HEAD(umount_list);
1751    struct path old_path;
1752    struct vfsmount *mnt = NULL;
1753    int err = mount_is_safe(path);
1754    if (err)
1755        return err;
1756    if (!old_name || !*old_name)
1757        return -EINVAL;
1758    err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
1759    if (err)
1760        return err;
1761
1762    err = lock_mount(path);
1763    if (err)
1764        goto out;
1765
1766    err = -EINVAL;
1767    if (IS_MNT_UNBINDABLE(old_path.mnt))
1768        goto out2;
1769
1770    if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
1771        goto out2;
1772
1773    err = -ENOMEM;
1774    if (recurse)
1775        mnt = copy_tree(old_path.mnt, old_path.dentry, 0);
1776    else
1777        mnt = clone_mnt(old_path.mnt, old_path.dentry, 0);
1778
1779    if (!mnt)
1780        goto out2;
1781
1782    err = graft_tree(mnt, path);
1783    if (err) {
1784        br_write_lock(vfsmount_lock);
1785        umount_tree(mnt, 0, &umount_list);
1786        br_write_unlock(vfsmount_lock);
1787    }
1788out2:
1789    unlock_mount(path);
1790    release_mounts(&umount_list);
1791out:
1792    path_put(&old_path);
1793    return err;
1794}
1795
1796static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
1797{
1798    int error = 0;
1799    int readonly_request = 0;
1800
1801    if (ms_flags & MS_RDONLY)
1802        readonly_request = 1;
1803    if (readonly_request == __mnt_is_readonly(mnt))
1804        return 0;
1805
1806    if (readonly_request)
1807        error = mnt_make_readonly(mnt);
1808    else
1809        __mnt_unmake_readonly(mnt);
1810    return error;
1811}
1812
1813/*
1814 * change filesystem flags. dir should be a physical root of filesystem.
1815 * If you've mounted a non-root directory somewhere and want to do remount
1816 * on it - tough luck.
1817 */
1818static int do_remount(struct path *path, int flags, int mnt_flags,
1819              void *data)
1820{
1821    int err;
1822    struct super_block *sb = path->mnt->mnt_sb;
1823
1824    if (!capable(CAP_SYS_ADMIN))
1825        return -EPERM;
1826
1827    if (!check_mnt(path->mnt))
1828        return -EINVAL;
1829
1830    if (path->dentry != path->mnt->mnt_root)
1831        return -EINVAL;
1832
1833    err = security_sb_remount(sb, data);
1834    if (err)
1835        return err;
1836
1837    down_write(&sb->s_umount);
1838    if (flags & MS_BIND)
1839        err = change_mount_flags(path->mnt, flags);
1840    else
1841        err = do_remount_sb(sb, flags, data, 0);
1842    if (!err) {
1843        br_write_lock(vfsmount_lock);
1844        mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK;
1845        path->mnt->mnt_flags = mnt_flags;
1846        br_write_unlock(vfsmount_lock);
1847    }
1848    up_write(&sb->s_umount);
1849    if (!err) {
1850        br_write_lock(vfsmount_lock);
1851        touch_mnt_namespace(path->mnt->mnt_ns);
1852        br_write_unlock(vfsmount_lock);
1853    }
1854    return err;
1855}
1856
1857static inline int tree_contains_unbindable(struct vfsmount *mnt)
1858{
1859    struct vfsmount *p;
1860    for (p = mnt; p; p = next_mnt(p, mnt)) {
1861        if (IS_MNT_UNBINDABLE(p))
1862            return 1;
1863    }
1864    return 0;
1865}
1866
1867static int do_move_mount(struct path *path, char *old_name)
1868{
1869    struct path old_path, parent_path;
1870    struct vfsmount *p;
1871    int err = 0;
1872    if (!capable(CAP_SYS_ADMIN))
1873        return -EPERM;
1874    if (!old_name || !*old_name)
1875        return -EINVAL;
1876    err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
1877    if (err)
1878        return err;
1879
1880    err = lock_mount(path);
1881    if (err < 0)
1882        goto out;
1883
1884    err = -EINVAL;
1885    if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
1886        goto out1;
1887
1888    if (d_unlinked(path->dentry))
1889        goto out1;
1890
1891    err = -EINVAL;
1892    if (old_path.dentry != old_path.mnt->mnt_root)
1893        goto out1;
1894
1895    if (old_path.mnt == old_path.mnt->mnt_parent)
1896        goto out1;
1897
1898    if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1899          S_ISDIR(old_path.dentry->d_inode->i_mode))
1900        goto out1;
1901    /*
1902     * Don't move a mount residing in a shared parent.
1903     */
1904    if (old_path.mnt->mnt_parent &&
1905        IS_MNT_SHARED(old_path.mnt->mnt_parent))
1906        goto out1;
1907    /*
1908     * Don't move a mount tree containing unbindable mounts to a destination
1909     * mount which is shared.
1910     */
1911    if (IS_MNT_SHARED(path->mnt) &&
1912        tree_contains_unbindable(old_path.mnt))
1913        goto out1;
1914    err = -ELOOP;
1915    for (p = path->mnt; p->mnt_parent != p; p = p->mnt_parent)
1916        if (p == old_path.mnt)
1917            goto out1;
1918
1919    err = attach_recursive_mnt(old_path.mnt, path, &parent_path);
1920    if (err)
1921        goto out1;
1922
1923    /* if the mount is moved, it should no longer be expire
1924     * automatically */
1925    list_del_init(&old_path.mnt->mnt_expire);
1926out1:
1927    unlock_mount(path);
1928out:
1929    if (!err)
1930        path_put(&parent_path);
1931    path_put(&old_path);
1932    return err;
1933}
1934
1935static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
1936{
1937    int err;
1938    const char *subtype = strchr(fstype, '.');
1939    if (subtype) {
1940        subtype++;
1941        err = -EINVAL;
1942        if (!subtype[0])
1943            goto err;
1944    } else
1945        subtype = "";
1946
1947    mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
1948    err = -ENOMEM;
1949    if (!mnt->mnt_sb->s_subtype)
1950        goto err;
1951    return mnt;
1952
1953 err:
1954    mntput(mnt);
1955    return ERR_PTR(err);
1956}
1957
1958struct vfsmount *
1959do_kern_mount(const char *fstype, int flags, const char *name, void *data)
1960{
1961    struct file_system_type *type = get_fs_type(fstype);
1962    struct vfsmount *mnt;
1963    if (!type)
1964        return ERR_PTR(-ENODEV);
1965    mnt = vfs_kern_mount(type, flags, name, data);
1966    if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
1967        !mnt->mnt_sb->s_subtype)
1968        mnt = fs_set_subtype(mnt, fstype);
1969    put_filesystem(type);
1970    return mnt;
1971}
1972EXPORT_SYMBOL_GPL(do_kern_mount);
1973
1974/*
1975 * add a mount into a namespace's mount tree
1976 */
1977static int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
1978{
1979    int err;
1980
1981    mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
1982
1983    err = lock_mount(path);
1984    if (err)
1985        return err;
1986
1987    err = -EINVAL;
1988    if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(path->mnt))
1989        goto unlock;
1990
1991    /* Refuse the same filesystem on the same mount point */
1992    err = -EBUSY;
1993    if (path->mnt->mnt_sb == newmnt->mnt_sb &&
1994        path->mnt->mnt_root == path->dentry)
1995        goto unlock;
1996
1997    err = -EINVAL;
1998    if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
1999        goto unlock;
2000
2001    newmnt->mnt_flags = mnt_flags;
2002    err = graft_tree(newmnt, path);
2003
2004unlock:
2005    unlock_mount(path);
2006    return err;
2007}
2008
2009/*
2010 * create a new mount for userspace and request it to be added into the
2011 * namespace's tree
2012 */
2013static int do_new_mount(struct path *path, char *type, int flags,
2014            int mnt_flags, char *name, void *data)
2015{
2016    struct vfsmount *mnt;
2017    int err;
2018
2019    if (!type)
2020        return -EINVAL;
2021
2022    /* we need capabilities... */
2023    if (!capable(CAP_SYS_ADMIN))
2024        return -EPERM;
2025
2026    mnt = do_kern_mount(type, flags, name, data);
2027    if (IS_ERR(mnt))
2028        return PTR_ERR(mnt);
2029
2030    err = do_add_mount(mnt, path, mnt_flags);
2031    if (err)
2032        mntput(mnt);
2033    return err;
2034}
2035
2036int finish_automount(struct vfsmount *m, struct path *path)
2037{
2038    int err;
2039    /* The new mount record should have at least 2 refs to prevent it being
2040     * expired before we get a chance to add it
2041     */
2042    BUG_ON(mnt_get_count(m) < 2);
2043
2044    if (m->mnt_sb == path->mnt->mnt_sb &&
2045        m->mnt_root == path->dentry) {
2046        err = -ELOOP;
2047        goto fail;
2048    }
2049
2050    err = do_add_mount(m, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2051    if (!err)
2052        return 0;
2053fail:
2054    /* remove m from any expiration list it may be on */
2055    if (!list_empty(&m->mnt_expire)) {
2056        down_write(&namespace_sem);
2057        br_write_lock(vfsmount_lock);
2058        list_del_init(&m->mnt_expire);
2059        br_write_unlock(vfsmount_lock);
2060        up_write(&namespace_sem);
2061    }
2062    mntput(m);
2063    mntput(m);
2064    return err;
2065}
2066
2067/**
2068 * mnt_set_expiry - Put a mount on an expiration list
2069 * @mnt: The mount to list.
2070 * @expiry_list: The list to add the mount to.
2071 */
2072void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2073{
2074    down_write(&namespace_sem);
2075    br_write_lock(vfsmount_lock);
2076
2077    list_add_tail(&mnt->mnt_expire, expiry_list);
2078
2079    br_write_unlock(vfsmount_lock);
2080    up_write(&namespace_sem);
2081}
2082EXPORT_SYMBOL(mnt_set_expiry);
2083
2084/*
2085 * process a list of expirable mountpoints with the intent of discarding any
2086 * mountpoints that aren't in use and haven't been touched since last we came
2087 * here
2088 */
2089void mark_mounts_for_expiry(struct list_head *mounts)
2090{
2091    struct vfsmount *mnt, *next;
2092    LIST_HEAD(graveyard);
2093    LIST_HEAD(umounts);
2094
2095    if (list_empty(mounts))
2096        return;
2097
2098    down_write(&namespace_sem);
2099    br_write_lock(vfsmount_lock);
2100
2101    /* extract from the expiration list every vfsmount that matches the
2102     * following criteria:
2103     * - only referenced by its parent vfsmount
2104     * - still marked for expiry (marked on the last call here; marks are
2105     * cleared by mntput())
2106     */
2107    list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2108        if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2109            propagate_mount_busy(mnt, 1))
2110            continue;
2111        list_move(&mnt->mnt_expire, &graveyard);
2112    }
2113    while (!list_empty(&graveyard)) {
2114        mnt = list_first_entry(&graveyard, struct vfsmount, mnt_expire);
2115        touch_mnt_namespace(mnt->mnt_ns);
2116        umount_tree(mnt, 1, &umounts);
2117    }
2118    br_write_unlock(vfsmount_lock);
2119    up_write(&namespace_sem);
2120
2121    release_mounts(&umounts);
2122}
2123
2124EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2125
2126/*
2127 * Ripoff of 'select_parent()'
2128 *
2129 * search the list of submounts for a given mountpoint, and move any
2130 * shrinkable submounts to the 'graveyard' list.
2131 */
2132static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
2133{
2134    struct vfsmount *this_parent = parent;
2135    struct list_head *next;
2136    int found = 0;
2137
2138repeat:
2139    next = this_parent->mnt_mounts.next;
2140resume:
2141    while (next != &this_parent->mnt_mounts) {
2142        struct list_head *tmp = next;
2143        struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
2144
2145        next = tmp->next;
2146        if (!(mnt->mnt_flags & MNT_SHRINKABLE))
2147            continue;
2148        /*
2149         * Descend a level if the d_mounts list is non-empty.
2150         */
2151        if (!list_empty(&mnt->mnt_mounts)) {
2152            this_parent = mnt;
2153            goto repeat;
2154        }
2155
2156        if (!propagate_mount_busy(mnt, 1)) {
2157            list_move_tail(&mnt->mnt_expire, graveyard);
2158            found++;
2159        }
2160    }
2161    /*
2162     * All done at this level ... ascend and resume the search
2163     */
2164    if (this_parent != parent) {
2165        next = this_parent->mnt_child.next;
2166        this_parent = this_parent->mnt_parent;
2167        goto resume;
2168    }
2169    return found;
2170}
2171
2172/*
2173 * process a list of expirable mountpoints with the intent of discarding any
2174 * submounts of a specific parent mountpoint
2175 *
2176 * vfsmount_lock must be held for write
2177 */
2178static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts)
2179{
2180    LIST_HEAD(graveyard);
2181    struct vfsmount *m;
2182
2183    /* extract submounts of 'mountpoint' from the expiration list */
2184    while (select_submounts(mnt, &graveyard)) {
2185        while (!list_empty(&graveyard)) {
2186            m = list_first_entry(&graveyard, struct vfsmount,
2187                        mnt_expire);
2188            touch_mnt_namespace(m->mnt_ns);
2189            umount_tree(m, 1, umounts);
2190        }
2191    }
2192}
2193
2194/*
2195 * Some copy_from_user() implementations do not return the exact number of
2196 * bytes remaining to copy on a fault. But copy_mount_options() requires that.
2197 * Note that this function differs from copy_from_user() in that it will oops
2198 * on bad values of `to', rather than returning a short copy.
2199 */
2200static long exact_copy_from_user(void *to, const void __user * from,
2201                 unsigned long n)
2202{
2203    char *t = to;
2204    const char __user *f = from;
2205    char c;
2206
2207    if (!access_ok(VERIFY_READ, from, n))
2208        return n;
2209
2210    while (n) {
2211        if (__get_user(c, f)) {
2212            memset(t, 0, n);
2213            break;
2214        }
2215        *t++ = c;
2216        f++;
2217        n--;
2218    }
2219    return n;
2220}
2221
2222int copy_mount_options(const void __user * data, unsigned long *where)
2223{
2224    int i;
2225    unsigned long page;
2226    unsigned long size;
2227
2228    *where = 0;
2229    if (!data)
2230        return 0;
2231
2232    if (!(page = __get_free_page(GFP_KERNEL)))
2233        return -ENOMEM;
2234
2235    /* We only care that *some* data at the address the user
2236     * gave us is valid. Just in case, we'll zero
2237     * the remainder of the page.
2238     */
2239    /* copy_from_user cannot cross TASK_SIZE ! */
2240    size = TASK_SIZE - (unsigned long)data;
2241    if (size > PAGE_SIZE)
2242        size = PAGE_SIZE;
2243
2244    i = size - exact_copy_from_user((void *)page, data, size);
2245    if (!i) {
2246        free_page(page);
2247        return -EFAULT;
2248    }
2249    if (i != PAGE_SIZE)
2250        memset((char *)page + i, 0, PAGE_SIZE - i);
2251    *where = page;
2252    return 0;
2253}
2254
2255int copy_mount_string(const void __user *data, char **where)
2256{
2257    char *tmp;
2258
2259    if (!data) {
2260        *where = NULL;
2261        return 0;
2262    }
2263
2264    tmp = strndup_user(data, PAGE_SIZE);
2265    if (IS_ERR(tmp))
2266        return PTR_ERR(tmp);
2267
2268    *where = tmp;
2269    return 0;
2270}
2271
2272/*
2273 * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2274 * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2275 *
2276 * data is a (void *) that can point to any structure up to
2277 * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2278 * information (or be NULL).
2279 *
2280 * Pre-0.97 versions of mount() didn't have a flags word.
2281 * When the flags word was introduced its top half was required
2282 * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2283 * Therefore, if this magic number is present, it carries no information
2284 * and must be discarded.
2285 */
2286long do_mount(char *dev_name, char *dir_name, char *type_page,
2287          unsigned long flags, void *data_page)
2288{
2289    struct path path;
2290    int retval = 0;
2291    int mnt_flags = 0;
2292
2293    /* Discard magic */
2294    if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2295        flags &= ~MS_MGC_MSK;
2296
2297    /* Basic sanity checks */
2298
2299    if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
2300        return -EINVAL;
2301
2302    if (data_page)
2303        ((char *)data_page)[PAGE_SIZE - 1] = 0;
2304
2305    /* ... and get the mountpoint */
2306    retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
2307    if (retval)
2308        return retval;
2309
2310    retval = security_sb_mount(dev_name, &path,
2311                   type_page, flags, data_page);
2312    if (retval)
2313        goto dput_out;
2314
2315    /* Default to relatime unless overriden */
2316    if (!(flags & MS_NOATIME))
2317        mnt_flags |= MNT_RELATIME;
2318
2319    /* Separate the per-mountpoint flags */
2320    if (flags & MS_NOSUID)
2321        mnt_flags |= MNT_NOSUID;
2322    if (flags & MS_NODEV)
2323        mnt_flags |= MNT_NODEV;
2324    if (flags & MS_NOEXEC)
2325        mnt_flags |= MNT_NOEXEC;
2326    if (flags & MS_NOATIME)
2327        mnt_flags |= MNT_NOATIME;
2328    if (flags & MS_NODIRATIME)
2329        mnt_flags |= MNT_NODIRATIME;
2330    if (flags & MS_STRICTATIME)
2331        mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2332    if (flags & MS_RDONLY)
2333        mnt_flags |= MNT_READONLY;
2334
2335    flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2336           MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2337           MS_STRICTATIME);
2338
2339    if (flags & MS_REMOUNT)
2340        retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2341                    data_page);
2342    else if (flags & MS_BIND)
2343        retval = do_loopback(&path, dev_name, flags & MS_REC);
2344    else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2345        retval = do_change_type(&path, flags);
2346    else if (flags & MS_MOVE)
2347        retval = do_move_mount(&path, dev_name);
2348    else
2349        retval = do_new_mount(&path, type_page, flags, mnt_flags,
2350                      dev_name, data_page);
2351dput_out:
2352    path_put(&path);
2353    return retval;
2354}
2355
2356static struct mnt_namespace *alloc_mnt_ns(void)
2357{
2358    struct mnt_namespace *new_ns;
2359
2360    new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2361    if (!new_ns)
2362        return ERR_PTR(-ENOMEM);
2363    atomic_set(&new_ns->count, 1);
2364    new_ns->root = NULL;
2365    INIT_LIST_HEAD(&new_ns->list);
2366    init_waitqueue_head(&new_ns->poll);
2367    new_ns->event = 0;
2368    return new_ns;
2369}
2370
2371void mnt_make_longterm(struct vfsmount *mnt)
2372{
2373    __mnt_make_longterm(mnt);
2374}
2375
2376void mnt_make_shortterm(struct vfsmount *mnt)
2377{
2378#ifdef CONFIG_SMP
2379    if (atomic_add_unless(&mnt->mnt_longterm, -1, 1))
2380        return;
2381    br_write_lock(vfsmount_lock);
2382    atomic_dec(&mnt->mnt_longterm);
2383    br_write_unlock(vfsmount_lock);
2384#endif
2385}
2386
2387/*
2388 * Allocate a new namespace structure and populate it with contents
2389 * copied from the namespace of the passed in task structure.
2390 */
2391static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
2392        struct fs_struct *fs)
2393{
2394    struct mnt_namespace *new_ns;
2395    struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2396    struct vfsmount *p, *q;
2397
2398    new_ns = alloc_mnt_ns();
2399    if (IS_ERR(new_ns))
2400        return new_ns;
2401
2402    down_write(&namespace_sem);
2403    /* First pass: copy the tree topology */
2404    new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
2405                    CL_COPY_ALL | CL_EXPIRE);
2406    if (!new_ns->root) {
2407        up_write(&namespace_sem);
2408        kfree(new_ns);
2409        return ERR_PTR(-ENOMEM);
2410    }
2411    br_write_lock(vfsmount_lock);
2412    list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
2413    br_write_unlock(vfsmount_lock);
2414
2415    /*
2416     * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2417     * as belonging to new namespace. We have already acquired a private
2418     * fs_struct, so tsk->fs->lock is not needed.
2419     */
2420    p = mnt_ns->root;
2421    q = new_ns->root;
2422    while (p) {
2423        q->mnt_ns = new_ns;
2424        __mnt_make_longterm(q);
2425        if (fs) {
2426            if (p == fs->root.mnt) {
2427                fs->root.mnt = mntget(q);
2428                __mnt_make_longterm(q);
2429                mnt_make_shortterm(p);
2430                rootmnt = p;
2431            }
2432            if (p == fs->pwd.mnt) {
2433                fs->pwd.mnt = mntget(q);
2434                __mnt_make_longterm(q);
2435                mnt_make_shortterm(p);
2436                pwdmnt = p;
2437            }
2438        }
2439        p = next_mnt(p, mnt_ns->root);
2440        q = next_mnt(q, new_ns->root);
2441    }
2442    up_write(&namespace_sem);
2443
2444    if (rootmnt)
2445        mntput(rootmnt);
2446    if (pwdmnt)
2447        mntput(pwdmnt);
2448
2449    return new_ns;
2450}
2451
2452struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2453        struct fs_struct *new_fs)
2454{
2455    struct mnt_namespace *new_ns;
2456
2457    BUG_ON(!ns);
2458    get_mnt_ns(ns);
2459
2460    if (!(flags & CLONE_NEWNS))
2461        return ns;
2462
2463    new_ns = dup_mnt_ns(ns, new_fs);
2464
2465    put_mnt_ns(ns);
2466    return new_ns;
2467}
2468
2469/**
2470 * create_mnt_ns - creates a private namespace and adds a root filesystem
2471 * @mnt: pointer to the new root filesystem mountpoint
2472 */
2473struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
2474{
2475    struct mnt_namespace *new_ns;
2476
2477    new_ns = alloc_mnt_ns();
2478    if (!IS_ERR(new_ns)) {
2479        mnt->mnt_ns = new_ns;
2480        __mnt_make_longterm(mnt);
2481        new_ns->root = mnt;
2482        list_add(&new_ns->list, &new_ns->root->mnt_list);
2483    } else {
2484        mntput(mnt);
2485    }
2486    return new_ns;
2487}
2488EXPORT_SYMBOL(create_mnt_ns);
2489
2490struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
2491{
2492    struct mnt_namespace *ns;
2493    struct super_block *s;
2494    struct path path;
2495    int err;
2496
2497    ns = create_mnt_ns(mnt);
2498    if (IS_ERR(ns))
2499        return ERR_CAST(ns);
2500
2501    err = vfs_path_lookup(mnt->mnt_root, mnt,
2502            name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
2503
2504    put_mnt_ns(ns);
2505
2506    if (err)
2507        return ERR_PTR(err);
2508
2509    /* trade a vfsmount reference for active sb one */
2510    s = path.mnt->mnt_sb;
2511    atomic_inc(&s->s_active);
2512    mntput(path.mnt);
2513    /* lock the sucker */
2514    down_write(&s->s_umount);
2515    /* ... and return the root of (sub)tree on it */
2516    return path.dentry;
2517}
2518EXPORT_SYMBOL(mount_subtree);
2519
2520SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
2521        char __user *, type, unsigned long, flags, void __user *, data)
2522{
2523    int ret;
2524    char *kernel_type;
2525    char *kernel_dir;
2526    char *kernel_dev;
2527    unsigned long data_page;
2528
2529    ret = copy_mount_string(type, &kernel_type);
2530    if (ret < 0)
2531        goto out_type;
2532
2533    kernel_dir = getname(dir_name);
2534    if (IS_ERR(kernel_dir)) {
2535        ret = PTR_ERR(kernel_dir);
2536        goto out_dir;
2537    }
2538
2539    ret = copy_mount_string(dev_name, &kernel_dev);
2540    if (ret < 0)
2541        goto out_dev;
2542
2543    ret = copy_mount_options(data, &data_page);
2544    if (ret < 0)
2545        goto out_data;
2546
2547    ret = do_mount(kernel_dev, kernel_dir, kernel_type, flags,
2548        (void *) data_page);
2549
2550    free_page(data_page);
2551out_data:
2552    kfree(kernel_dev);
2553out_dev:
2554    putname(kernel_dir);
2555out_dir:
2556    kfree(kernel_type);
2557out_type:
2558    return ret;
2559}
2560
2561/*
2562 * pivot_root Semantics:
2563 * Moves the root file system of the current process to the directory put_old,
2564 * makes new_root as the new root file system of the current process, and sets
2565 * root/cwd of all processes which had them on the current root to new_root.
2566 *
2567 * Restrictions:
2568 * The new_root and put_old must be directories, and must not be on the
2569 * same file system as the current process root. The put_old must be
2570 * underneath new_root, i.e. adding a non-zero number of /.. to the string
2571 * pointed to by put_old must yield the same directory as new_root. No other
2572 * file system may be mounted on put_old. After all, new_root is a mountpoint.
2573 *
2574 * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
2575 * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
2576 * in this situation.
2577 *
2578 * Notes:
2579 * - we don't move root/cwd if they are not at the root (reason: if something
2580 * cared enough to change them, it's probably wrong to force them elsewhere)
2581 * - it's okay to pick a root that isn't the root of a file system, e.g.
2582 * /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
2583 * though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
2584 * first.
2585 */
2586SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
2587        const char __user *, put_old)
2588{
2589    struct vfsmount *tmp;
2590    struct path new, old, parent_path, root_parent, root;
2591    int error;
2592
2593    if (!capable(CAP_SYS_ADMIN))
2594        return -EPERM;
2595
2596    error = user_path_dir(new_root, &new);
2597    if (error)
2598        goto out0;
2599
2600    error = user_path_dir(put_old, &old);
2601    if (error)
2602        goto out1;
2603
2604    error = security_sb_pivotroot(&old, &new);
2605    if (error)
2606        goto out2;
2607
2608    get_fs_root(current->fs, &root);
2609    error = lock_mount(&old);
2610    if (error)
2611        goto out3;
2612
2613    error = -EINVAL;
2614    if (IS_MNT_SHARED(old.mnt) ||
2615        IS_MNT_SHARED(new.mnt->mnt_parent) ||
2616        IS_MNT_SHARED(root.mnt->mnt_parent))
2617        goto out4;
2618    if (!check_mnt(root.mnt) || !check_mnt(new.mnt))
2619        goto out4;
2620    error = -ENOENT;
2621    if (d_unlinked(new.dentry))
2622        goto out4;
2623    if (d_unlinked(old.dentry))
2624        goto out4;
2625    error = -EBUSY;
2626    if (new.mnt == root.mnt ||
2627        old.mnt == root.mnt)
2628        goto out4; /* loop, on the same file system */
2629    error = -EINVAL;
2630    if (root.mnt->mnt_root != root.dentry)
2631        goto out4; /* not a mountpoint */
2632    if (root.mnt->mnt_parent == root.mnt)
2633        goto out4; /* not attached */
2634    if (new.mnt->mnt_root != new.dentry)
2635        goto out4; /* not a mountpoint */
2636    if (new.mnt->mnt_parent == new.mnt)
2637        goto out4; /* not attached */
2638    /* make sure we can reach put_old from new_root */
2639    tmp = old.mnt;
2640    if (tmp != new.mnt) {
2641        for (;;) {
2642            if (tmp->mnt_parent == tmp)
2643                goto out4; /* already mounted on put_old */
2644            if (tmp->mnt_parent == new.mnt)
2645                break;
2646            tmp = tmp->mnt_parent;
2647        }
2648        if (!is_subdir(tmp->mnt_mountpoint, new.dentry))
2649            goto out4;
2650    } else if (!is_subdir(old.dentry, new.dentry))
2651        goto out4;
2652    br_write_lock(vfsmount_lock);
2653    detach_mnt(new.mnt, &parent_path);
2654    detach_mnt(root.mnt, &root_parent);
2655    /* mount old root on put_old */
2656    attach_mnt(root.mnt, &old);
2657    /* mount new_root on / */
2658    attach_mnt(new.mnt, &root_parent);
2659    touch_mnt_namespace(current->nsproxy->mnt_ns);
2660    br_write_unlock(vfsmount_lock);
2661    chroot_fs_refs(&root, &new);
2662    error = 0;
2663out4:
2664    unlock_mount(&old);
2665    if (!error) {
2666        path_put(&root_parent);
2667        path_put(&parent_path);
2668    }
2669out3:
2670    path_put(&root);
2671out2:
2672    path_put(&old);
2673out1:
2674    path_put(&new);
2675out0:
2676    return error;
2677}
2678
2679static void __init init_mount_tree(void)
2680{
2681    struct vfsmount *mnt;
2682    struct mnt_namespace *ns;
2683    struct path root;
2684
2685    mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
2686    if (IS_ERR(mnt))
2687        panic("Can't create rootfs");
2688
2689    ns = create_mnt_ns(mnt);
2690    if (IS_ERR(ns))
2691        panic("Can't allocate initial namespace");
2692
2693    init_task.nsproxy->mnt_ns = ns;
2694    get_mnt_ns(ns);
2695
2696    root.mnt = ns->root;
2697    root.dentry = ns->root->mnt_root;
2698
2699    set_fs_pwd(current->fs, &root);
2700    set_fs_root(current->fs, &root);
2701}
2702
2703void __init mnt_init(void)
2704{
2705    unsigned u;
2706    int err;
2707
2708    init_rwsem(&namespace_sem);
2709
2710    mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
2711            0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2712
2713    mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2714
2715    if (!mount_hashtable)
2716        panic("Failed to allocate mount hash table\n");
2717
2718    printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
2719
2720    for (u = 0; u < HASH_SIZE; u++)
2721        INIT_LIST_HEAD(&mount_hashtable[u]);
2722
2723    br_lock_init(vfsmount_lock);
2724
2725    err = sysfs_init();
2726    if (err)
2727        printk(KERN_WARNING "%s: sysfs_init error: %d\n",
2728            __func__, err);
2729    fs_kobj = kobject_create_and_add("fs", NULL);
2730    if (!fs_kobj)
2731        printk(KERN_WARNING "%s: kobj create error\n", __func__);
2732    init_rootfs();
2733    init_mount_tree();
2734}
2735
2736void put_mnt_ns(struct mnt_namespace *ns)
2737{
2738    LIST_HEAD(umount_list);
2739
2740    if (!atomic_dec_and_test(&ns->count))
2741        return;
2742    down_write(&namespace_sem);
2743    br_write_lock(vfsmount_lock);
2744    umount_tree(ns->root, 0, &umount_list);
2745    br_write_unlock(vfsmount_lock);
2746    up_write(&namespace_sem);
2747    release_mounts(&umount_list);
2748    kfree(ns);
2749}
2750EXPORT_SYMBOL(put_mnt_ns);
2751
2752struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
2753{
2754    struct vfsmount *mnt;
2755    mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
2756    if (!IS_ERR(mnt)) {
2757        /*
2758         * it is a longterm mount, don't release mnt until
2759         * we unmount before file sys is unregistered
2760        */
2761        mnt_make_longterm(mnt);
2762    }
2763    return mnt;
2764}
2765EXPORT_SYMBOL_GPL(kern_mount_data);
2766
2767void kern_unmount(struct vfsmount *mnt)
2768{
2769    /* release long term mount so mount point can be released */
2770    if (!IS_ERR_OR_NULL(mnt)) {
2771        mnt_make_shortterm(mnt);
2772        mntput(mnt);
2773    }
2774}
2775EXPORT_SYMBOL(kern_unmount);
2776
2777bool our_mnt(struct vfsmount *mnt)
2778{
2779    return check_mnt(mnt);
2780}
2781

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