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TOMOYO Linux Cross Reference
Linux/fs/namespace.c

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  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/export.h>
 13 #include <linux/capability.h>
 14 #include <linux/mnt_namespace.h>
 15 #include <linux/user_namespace.h>
 16 #include <linux/namei.h>
 17 #include <linux/security.h>
 18 #include <linux/idr.h>
 19 #include <linux/init.h>         /* init_rootfs */
 20 #include <linux/fs_struct.h>    /* get_fs_root et.al. */
 21 #include <linux/fsnotify.h>     /* fsnotify_vfsmount_delete */
 22 #include <linux/uaccess.h>
 23 #include <linux/proc_ns.h>
 24 #include <linux/magic.h>
 25 #include <linux/bootmem.h>
 26 #include <linux/task_work.h>
 27 #include "pnode.h"
 28 #include "internal.h"
 29 
 30 static unsigned int m_hash_mask __read_mostly;
 31 static unsigned int m_hash_shift __read_mostly;
 32 static unsigned int mp_hash_mask __read_mostly;
 33 static unsigned int mp_hash_shift __read_mostly;
 34 
 35 static __initdata unsigned long mhash_entries;
 36 static int __init set_mhash_entries(char *str)
 37 {
 38         if (!str)
 39                 return 0;
 40         mhash_entries = simple_strtoul(str, &str, 0);
 41         return 1;
 42 }
 43 __setup("mhash_entries=", set_mhash_entries);
 44 
 45 static __initdata unsigned long mphash_entries;
 46 static int __init set_mphash_entries(char *str)
 47 {
 48         if (!str)
 49                 return 0;
 50         mphash_entries = simple_strtoul(str, &str, 0);
 51         return 1;
 52 }
 53 __setup("mphash_entries=", set_mphash_entries);
 54 
 55 static u64 event;
 56 static DEFINE_IDA(mnt_id_ida);
 57 static DEFINE_IDA(mnt_group_ida);
 58 static DEFINE_SPINLOCK(mnt_id_lock);
 59 static int mnt_id_start = 0;
 60 static int mnt_group_start = 1;
 61 
 62 static struct hlist_head *mount_hashtable __read_mostly;
 63 static struct hlist_head *mountpoint_hashtable __read_mostly;
 64 static struct kmem_cache *mnt_cache __read_mostly;
 65 static DECLARE_RWSEM(namespace_sem);
 66 
 67 /* /sys/fs */
 68 struct kobject *fs_kobj;
 69 EXPORT_SYMBOL_GPL(fs_kobj);
 70 
 71 /*
 72  * vfsmount lock may be taken for read to prevent changes to the
 73  * vfsmount hash, ie. during mountpoint lookups or walking back
 74  * up the tree.
 75  *
 76  * It should be taken for write in all cases where the vfsmount
 77  * tree or hash is modified or when a vfsmount structure is modified.
 78  */
 79 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
 80 
 81 static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
 82 {
 83         unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
 84         tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
 85         tmp = tmp + (tmp >> m_hash_shift);
 86         return &mount_hashtable[tmp & m_hash_mask];
 87 }
 88 
 89 static inline struct hlist_head *mp_hash(struct dentry *dentry)
 90 {
 91         unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
 92         tmp = tmp + (tmp >> mp_hash_shift);
 93         return &mountpoint_hashtable[tmp & mp_hash_mask];
 94 }
 95 
 96 /*
 97  * allocation is serialized by namespace_sem, but we need the spinlock to
 98  * serialize with freeing.
 99  */
100 static int mnt_alloc_id(struct mount *mnt)
101 {
102         int res;
103 
104 retry:
105         ida_pre_get(&mnt_id_ida, GFP_KERNEL);
106         spin_lock(&mnt_id_lock);
107         res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
108         if (!res)
109                 mnt_id_start = mnt->mnt_id + 1;
110         spin_unlock(&mnt_id_lock);
111         if (res == -EAGAIN)
112                 goto retry;
113 
114         return res;
115 }
116 
117 static void mnt_free_id(struct mount *mnt)
118 {
119         int id = mnt->mnt_id;
120         spin_lock(&mnt_id_lock);
121         ida_remove(&mnt_id_ida, id);
122         if (mnt_id_start > id)
123                 mnt_id_start = id;
124         spin_unlock(&mnt_id_lock);
125 }
126 
127 /*
128  * Allocate a new peer group ID
129  *
130  * mnt_group_ida is protected by namespace_sem
131  */
132 static int mnt_alloc_group_id(struct mount *mnt)
133 {
134         int res;
135 
136         if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
137                 return -ENOMEM;
138 
139         res = ida_get_new_above(&mnt_group_ida,
140                                 mnt_group_start,
141                                 &mnt->mnt_group_id);
142         if (!res)
143                 mnt_group_start = mnt->mnt_group_id + 1;
144 
145         return res;
146 }
147 
148 /*
149  * Release a peer group ID
150  */
151 void mnt_release_group_id(struct mount *mnt)
152 {
153         int id = mnt->mnt_group_id;
154         ida_remove(&mnt_group_ida, id);
155         if (mnt_group_start > id)
156                 mnt_group_start = id;
157         mnt->mnt_group_id = 0;
158 }
159 
160 /*
161  * vfsmount lock must be held for read
162  */
163 static inline void mnt_add_count(struct mount *mnt, int n)
164 {
165 #ifdef CONFIG_SMP
166         this_cpu_add(mnt->mnt_pcp->mnt_count, n);
167 #else
168         preempt_disable();
169         mnt->mnt_count += n;
170         preempt_enable();
171 #endif
172 }
173 
174 /*
175  * vfsmount lock must be held for write
176  */
177 unsigned int mnt_get_count(struct mount *mnt)
178 {
179 #ifdef CONFIG_SMP
180         unsigned int count = 0;
181         int cpu;
182 
183         for_each_possible_cpu(cpu) {
184                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
185         }
186 
187         return count;
188 #else
189         return mnt->mnt_count;
190 #endif
191 }
192 
193 static void drop_mountpoint(struct fs_pin *p)
194 {
195         struct mount *m = container_of(p, struct mount, mnt_umount);
196         dput(m->mnt_ex_mountpoint);
197         pin_remove(p);
198         mntput(&m->mnt);
199 }
200 
201 static struct mount *alloc_vfsmnt(const char *name)
202 {
203         struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
204         if (mnt) {
205                 int err;
206 
207                 err = mnt_alloc_id(mnt);
208                 if (err)
209                         goto out_free_cache;
210 
211                 if (name) {
212                         mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
213                         if (!mnt->mnt_devname)
214                                 goto out_free_id;
215                 }
216 
217 #ifdef CONFIG_SMP
218                 mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
219                 if (!mnt->mnt_pcp)
220                         goto out_free_devname;
221 
222                 this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
223 #else
224                 mnt->mnt_count = 1;
225                 mnt->mnt_writers = 0;
226 #endif
227 
228                 INIT_HLIST_NODE(&mnt->mnt_hash);
229                 INIT_LIST_HEAD(&mnt->mnt_child);
230                 INIT_LIST_HEAD(&mnt->mnt_mounts);
231                 INIT_LIST_HEAD(&mnt->mnt_list);
232                 INIT_LIST_HEAD(&mnt->mnt_expire);
233                 INIT_LIST_HEAD(&mnt->mnt_share);
234                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
235                 INIT_LIST_HEAD(&mnt->mnt_slave);
236                 INIT_HLIST_NODE(&mnt->mnt_mp_list);
237 #ifdef CONFIG_FSNOTIFY
238                 INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
239 #endif
240                 init_fs_pin(&mnt->mnt_umount, drop_mountpoint);
241         }
242         return mnt;
243 
244 #ifdef CONFIG_SMP
245 out_free_devname:
246         kfree_const(mnt->mnt_devname);
247 #endif
248 out_free_id:
249         mnt_free_id(mnt);
250 out_free_cache:
251         kmem_cache_free(mnt_cache, mnt);
252         return NULL;
253 }
254 
255 /*
256  * Most r/o checks on a fs are for operations that take
257  * discrete amounts of time, like a write() or unlink().
258  * We must keep track of when those operations start
259  * (for permission checks) and when they end, so that
260  * we can determine when writes are able to occur to
261  * a filesystem.
262  */
263 /*
264  * __mnt_is_readonly: check whether a mount is read-only
265  * @mnt: the mount to check for its write status
266  *
267  * This shouldn't be used directly ouside of the VFS.
268  * It does not guarantee that the filesystem will stay
269  * r/w, just that it is right *now*.  This can not and
270  * should not be used in place of IS_RDONLY(inode).
271  * mnt_want/drop_write() will _keep_ the filesystem
272  * r/w.
273  */
274 int __mnt_is_readonly(struct vfsmount *mnt)
275 {
276         if (mnt->mnt_flags & MNT_READONLY)
277                 return 1;
278         if (mnt->mnt_sb->s_flags & MS_RDONLY)
279                 return 1;
280         return 0;
281 }
282 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
283 
284 static inline void mnt_inc_writers(struct mount *mnt)
285 {
286 #ifdef CONFIG_SMP
287         this_cpu_inc(mnt->mnt_pcp->mnt_writers);
288 #else
289         mnt->mnt_writers++;
290 #endif
291 }
292 
293 static inline void mnt_dec_writers(struct mount *mnt)
294 {
295 #ifdef CONFIG_SMP
296         this_cpu_dec(mnt->mnt_pcp->mnt_writers);
297 #else
298         mnt->mnt_writers--;
299 #endif
300 }
301 
302 static unsigned int mnt_get_writers(struct mount *mnt)
303 {
304 #ifdef CONFIG_SMP
305         unsigned int count = 0;
306         int cpu;
307 
308         for_each_possible_cpu(cpu) {
309                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
310         }
311 
312         return count;
313 #else
314         return mnt->mnt_writers;
315 #endif
316 }
317 
318 static int mnt_is_readonly(struct vfsmount *mnt)
319 {
320         if (mnt->mnt_sb->s_readonly_remount)
321                 return 1;
322         /* Order wrt setting s_flags/s_readonly_remount in do_remount() */
323         smp_rmb();
324         return __mnt_is_readonly(mnt);
325 }
326 
327 /*
328  * Most r/o & frozen checks on a fs are for operations that take discrete
329  * amounts of time, like a write() or unlink().  We must keep track of when
330  * those operations start (for permission checks) and when they end, so that we
331  * can determine when writes are able to occur to a filesystem.
332  */
333 /**
334  * __mnt_want_write - get write access to a mount without freeze protection
335  * @m: the mount on which to take a write
336  *
337  * This tells the low-level filesystem that a write is about to be performed to
338  * it, and makes sure that writes are allowed (mnt it read-write) before
339  * returning success. This operation does not protect against filesystem being
340  * frozen. When the write operation is finished, __mnt_drop_write() must be
341  * called. This is effectively a refcount.
342  */
343 int __mnt_want_write(struct vfsmount *m)
344 {
345         struct mount *mnt = real_mount(m);
346         int ret = 0;
347 
348         preempt_disable();
349         mnt_inc_writers(mnt);
350         /*
351          * The store to mnt_inc_writers must be visible before we pass
352          * MNT_WRITE_HOLD loop below, so that the slowpath can see our
353          * incremented count after it has set MNT_WRITE_HOLD.
354          */
355         smp_mb();
356         while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
357                 cpu_relax();
358         /*
359          * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
360          * be set to match its requirements. So we must not load that until
361          * MNT_WRITE_HOLD is cleared.
362          */
363         smp_rmb();
364         if (mnt_is_readonly(m)) {
365                 mnt_dec_writers(mnt);
366                 ret = -EROFS;
367         }
368         preempt_enable();
369 
370         return ret;
371 }
372 
373 /**
374  * mnt_want_write - get write access to a mount
375  * @m: the mount on which to take a write
376  *
377  * This tells the low-level filesystem that a write is about to be performed to
378  * it, and makes sure that writes are allowed (mount is read-write, filesystem
379  * is not frozen) before returning success.  When the write operation is
380  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
381  */
382 int mnt_want_write(struct vfsmount *m)
383 {
384         int ret;
385 
386         sb_start_write(m->mnt_sb);
387         ret = __mnt_want_write(m);
388         if (ret)
389                 sb_end_write(m->mnt_sb);
390         return ret;
391 }
392 EXPORT_SYMBOL_GPL(mnt_want_write);
393 
394 /**
395  * mnt_clone_write - get write access to a mount
396  * @mnt: the mount on which to take a write
397  *
398  * This is effectively like mnt_want_write, except
399  * it must only be used to take an extra write reference
400  * on a mountpoint that we already know has a write reference
401  * on it. This allows some optimisation.
402  *
403  * After finished, mnt_drop_write must be called as usual to
404  * drop the reference.
405  */
406 int mnt_clone_write(struct vfsmount *mnt)
407 {
408         /* superblock may be r/o */
409         if (__mnt_is_readonly(mnt))
410                 return -EROFS;
411         preempt_disable();
412         mnt_inc_writers(real_mount(mnt));
413         preempt_enable();
414         return 0;
415 }
416 EXPORT_SYMBOL_GPL(mnt_clone_write);
417 
418 /**
419  * __mnt_want_write_file - get write access to a file's mount
420  * @file: the file who's mount on which to take a write
421  *
422  * This is like __mnt_want_write, but it takes a file and can
423  * do some optimisations if the file is open for write already
424  */
425 int __mnt_want_write_file(struct file *file)
426 {
427         if (!(file->f_mode & FMODE_WRITER))
428                 return __mnt_want_write(file->f_path.mnt);
429         else
430                 return mnt_clone_write(file->f_path.mnt);
431 }
432 
433 /**
434  * mnt_want_write_file - get write access to a file's mount
435  * @file: the file who's mount on which to take a write
436  *
437  * This is like mnt_want_write, but it takes a file and can
438  * do some optimisations if the file is open for write already
439  */
440 int mnt_want_write_file(struct file *file)
441 {
442         int ret;
443 
444         sb_start_write(file->f_path.mnt->mnt_sb);
445         ret = __mnt_want_write_file(file);
446         if (ret)
447                 sb_end_write(file->f_path.mnt->mnt_sb);
448         return ret;
449 }
450 EXPORT_SYMBOL_GPL(mnt_want_write_file);
451 
452 /**
453  * __mnt_drop_write - give up write access to a mount
454  * @mnt: the mount on which to give up write access
455  *
456  * Tells the low-level filesystem that we are done
457  * performing writes to it.  Must be matched with
458  * __mnt_want_write() call above.
459  */
460 void __mnt_drop_write(struct vfsmount *mnt)
461 {
462         preempt_disable();
463         mnt_dec_writers(real_mount(mnt));
464         preempt_enable();
465 }
466 
467 /**
468  * mnt_drop_write - give up write access to a mount
469  * @mnt: the mount on which to give up write access
470  *
471  * Tells the low-level filesystem that we are done performing writes to it and
472  * also allows filesystem to be frozen again.  Must be matched with
473  * mnt_want_write() call above.
474  */
475 void mnt_drop_write(struct vfsmount *mnt)
476 {
477         __mnt_drop_write(mnt);
478         sb_end_write(mnt->mnt_sb);
479 }
480 EXPORT_SYMBOL_GPL(mnt_drop_write);
481 
482 void __mnt_drop_write_file(struct file *file)
483 {
484         __mnt_drop_write(file->f_path.mnt);
485 }
486 
487 void mnt_drop_write_file(struct file *file)
488 {
489         mnt_drop_write(file->f_path.mnt);
490 }
491 EXPORT_SYMBOL(mnt_drop_write_file);
492 
493 static int mnt_make_readonly(struct mount *mnt)
494 {
495         int ret = 0;
496 
497         lock_mount_hash();
498         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
499         /*
500          * After storing MNT_WRITE_HOLD, we'll read the counters. This store
501          * should be visible before we do.
502          */
503         smp_mb();
504 
505         /*
506          * With writers on hold, if this value is zero, then there are
507          * definitely no active writers (although held writers may subsequently
508          * increment the count, they'll have to wait, and decrement it after
509          * seeing MNT_READONLY).
510          *
511          * It is OK to have counter incremented on one CPU and decremented on
512          * another: the sum will add up correctly. The danger would be when we
513          * sum up each counter, if we read a counter before it is incremented,
514          * but then read another CPU's count which it has been subsequently
515          * decremented from -- we would see more decrements than we should.
516          * MNT_WRITE_HOLD protects against this scenario, because
517          * mnt_want_write first increments count, then smp_mb, then spins on
518          * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
519          * we're counting up here.
520          */
521         if (mnt_get_writers(mnt) > 0)
522                 ret = -EBUSY;
523         else
524                 mnt->mnt.mnt_flags |= MNT_READONLY;
525         /*
526          * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
527          * that become unheld will see MNT_READONLY.
528          */
529         smp_wmb();
530         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
531         unlock_mount_hash();
532         return ret;
533 }
534 
535 static void __mnt_unmake_readonly(struct mount *mnt)
536 {
537         lock_mount_hash();
538         mnt->mnt.mnt_flags &= ~MNT_READONLY;
539         unlock_mount_hash();
540 }
541 
542 int sb_prepare_remount_readonly(struct super_block *sb)
543 {
544         struct mount *mnt;
545         int err = 0;
546 
547         /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
548         if (atomic_long_read(&sb->s_remove_count))
549                 return -EBUSY;
550 
551         lock_mount_hash();
552         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
553                 if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
554                         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
555                         smp_mb();
556                         if (mnt_get_writers(mnt) > 0) {
557                                 err = -EBUSY;
558                                 break;
559                         }
560                 }
561         }
562         if (!err && atomic_long_read(&sb->s_remove_count))
563                 err = -EBUSY;
564 
565         if (!err) {
566                 sb->s_readonly_remount = 1;
567                 smp_wmb();
568         }
569         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
570                 if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
571                         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
572         }
573         unlock_mount_hash();
574 
575         return err;
576 }
577 
578 static void free_vfsmnt(struct mount *mnt)
579 {
580         kfree_const(mnt->mnt_devname);
581 #ifdef CONFIG_SMP
582         free_percpu(mnt->mnt_pcp);
583 #endif
584         kmem_cache_free(mnt_cache, mnt);
585 }
586 
587 static void delayed_free_vfsmnt(struct rcu_head *head)
588 {
589         free_vfsmnt(container_of(head, struct mount, mnt_rcu));
590 }
591 
592 /* call under rcu_read_lock */
593 bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
594 {
595         struct mount *mnt;
596         if (read_seqretry(&mount_lock, seq))
597                 return false;
598         if (bastard == NULL)
599                 return true;
600         mnt = real_mount(bastard);
601         mnt_add_count(mnt, 1);
602         if (likely(!read_seqretry(&mount_lock, seq)))
603                 return true;
604         if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
605                 mnt_add_count(mnt, -1);
606                 return false;
607         }
608         rcu_read_unlock();
609         mntput(bastard);
610         rcu_read_lock();
611         return false;
612 }
613 
614 /*
615  * find the first mount at @dentry on vfsmount @mnt.
616  * call under rcu_read_lock()
617  */
618 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
619 {
620         struct hlist_head *head = m_hash(mnt, dentry);
621         struct mount *p;
622 
623         hlist_for_each_entry_rcu(p, head, mnt_hash)
624                 if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
625                         return p;
626         return NULL;
627 }
628 
629 /*
630  * find the last mount at @dentry on vfsmount @mnt.
631  * mount_lock must be held.
632  */
633 struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
634 {
635         struct mount *p, *res = NULL;
636         p = __lookup_mnt(mnt, dentry);
637         if (!p)
638                 goto out;
639         if (!(p->mnt.mnt_flags & MNT_UMOUNT))
640                 res = p;
641         hlist_for_each_entry_continue(p, mnt_hash) {
642                 if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
643                         break;
644                 if (!(p->mnt.mnt_flags & MNT_UMOUNT))
645                         res = p;
646         }
647 out:
648         return res;
649 }
650 
651 /*
652  * lookup_mnt - Return the first child mount mounted at path
653  *
654  * "First" means first mounted chronologically.  If you create the
655  * following mounts:
656  *
657  * mount /dev/sda1 /mnt
658  * mount /dev/sda2 /mnt
659  * mount /dev/sda3 /mnt
660  *
661  * Then lookup_mnt() on the base /mnt dentry in the root mount will
662  * return successively the root dentry and vfsmount of /dev/sda1, then
663  * /dev/sda2, then /dev/sda3, then NULL.
664  *
665  * lookup_mnt takes a reference to the found vfsmount.
666  */
667 struct vfsmount *lookup_mnt(struct path *path)
668 {
669         struct mount *child_mnt;
670         struct vfsmount *m;
671         unsigned seq;
672 
673         rcu_read_lock();
674         do {
675                 seq = read_seqbegin(&mount_lock);
676                 child_mnt = __lookup_mnt(path->mnt, path->dentry);
677                 m = child_mnt ? &child_mnt->mnt : NULL;
678         } while (!legitimize_mnt(m, seq));
679         rcu_read_unlock();
680         return m;
681 }
682 
683 /*
684  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
685  *                         current mount namespace.
686  *
687  * The common case is dentries are not mountpoints at all and that
688  * test is handled inline.  For the slow case when we are actually
689  * dealing with a mountpoint of some kind, walk through all of the
690  * mounts in the current mount namespace and test to see if the dentry
691  * is a mountpoint.
692  *
693  * The mount_hashtable is not usable in the context because we
694  * need to identify all mounts that may be in the current mount
695  * namespace not just a mount that happens to have some specified
696  * parent mount.
697  */
698 bool __is_local_mountpoint(struct dentry *dentry)
699 {
700         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
701         struct mount *mnt;
702         bool is_covered = false;
703 
704         if (!d_mountpoint(dentry))
705                 goto out;
706 
707         down_read(&namespace_sem);
708         list_for_each_entry(mnt, &ns->list, mnt_list) {
709                 is_covered = (mnt->mnt_mountpoint == dentry);
710                 if (is_covered)
711                         break;
712         }
713         up_read(&namespace_sem);
714 out:
715         return is_covered;
716 }
717 
718 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
719 {
720         struct hlist_head *chain = mp_hash(dentry);
721         struct mountpoint *mp;
722 
723         hlist_for_each_entry(mp, chain, m_hash) {
724                 if (mp->m_dentry == dentry) {
725                         /* might be worth a WARN_ON() */
726                         if (d_unlinked(dentry))
727                                 return ERR_PTR(-ENOENT);
728                         mp->m_count++;
729                         return mp;
730                 }
731         }
732         return NULL;
733 }
734 
735 static struct mountpoint *new_mountpoint(struct dentry *dentry)
736 {
737         struct hlist_head *chain = mp_hash(dentry);
738         struct mountpoint *mp;
739         int ret;
740 
741         mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
742         if (!mp)
743                 return ERR_PTR(-ENOMEM);
744 
745         ret = d_set_mounted(dentry);
746         if (ret) {
747                 kfree(mp);
748                 return ERR_PTR(ret);
749         }
750 
751         mp->m_dentry = dentry;
752         mp->m_count = 1;
753         hlist_add_head(&mp->m_hash, chain);
754         INIT_HLIST_HEAD(&mp->m_list);
755         return mp;
756 }
757 
758 static void put_mountpoint(struct mountpoint *mp)
759 {
760         if (!--mp->m_count) {
761                 struct dentry *dentry = mp->m_dentry;
762                 BUG_ON(!hlist_empty(&mp->m_list));
763                 spin_lock(&dentry->d_lock);
764                 dentry->d_flags &= ~DCACHE_MOUNTED;
765                 spin_unlock(&dentry->d_lock);
766                 hlist_del(&mp->m_hash);
767                 kfree(mp);
768         }
769 }
770 
771 static inline int check_mnt(struct mount *mnt)
772 {
773         return mnt->mnt_ns == current->nsproxy->mnt_ns;
774 }
775 
776 /*
777  * vfsmount lock must be held for write
778  */
779 static void touch_mnt_namespace(struct mnt_namespace *ns)
780 {
781         if (ns) {
782                 ns->event = ++event;
783                 wake_up_interruptible(&ns->poll);
784         }
785 }
786 
787 /*
788  * vfsmount lock must be held for write
789  */
790 static void __touch_mnt_namespace(struct mnt_namespace *ns)
791 {
792         if (ns && ns->event != event) {
793                 ns->event = event;
794                 wake_up_interruptible(&ns->poll);
795         }
796 }
797 
798 /*
799  * vfsmount lock must be held for write
800  */
801 static void unhash_mnt(struct mount *mnt)
802 {
803         mnt->mnt_parent = mnt;
804         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
805         list_del_init(&mnt->mnt_child);
806         hlist_del_init_rcu(&mnt->mnt_hash);
807         hlist_del_init(&mnt->mnt_mp_list);
808         put_mountpoint(mnt->mnt_mp);
809         mnt->mnt_mp = NULL;
810 }
811 
812 /*
813  * vfsmount lock must be held for write
814  */
815 static void detach_mnt(struct mount *mnt, struct path *old_path)
816 {
817         old_path->dentry = mnt->mnt_mountpoint;
818         old_path->mnt = &mnt->mnt_parent->mnt;
819         unhash_mnt(mnt);
820 }
821 
822 /*
823  * vfsmount lock must be held for write
824  */
825 static void umount_mnt(struct mount *mnt)
826 {
827         /* old mountpoint will be dropped when we can do that */
828         mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
829         unhash_mnt(mnt);
830 }
831 
832 /*
833  * vfsmount lock must be held for write
834  */
835 void mnt_set_mountpoint(struct mount *mnt,
836                         struct mountpoint *mp,
837                         struct mount *child_mnt)
838 {
839         mp->m_count++;
840         mnt_add_count(mnt, 1);  /* essentially, that's mntget */
841         child_mnt->mnt_mountpoint = dget(mp->m_dentry);
842         child_mnt->mnt_parent = mnt;
843         child_mnt->mnt_mp = mp;
844         hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
845 }
846 
847 /*
848  * vfsmount lock must be held for write
849  */
850 static void attach_mnt(struct mount *mnt,
851                         struct mount *parent,
852                         struct mountpoint *mp)
853 {
854         mnt_set_mountpoint(parent, mp, mnt);
855         hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
856         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
857 }
858 
859 static void attach_shadowed(struct mount *mnt,
860                         struct mount *parent,
861                         struct mount *shadows)
862 {
863         if (shadows) {
864                 hlist_add_behind_rcu(&mnt->mnt_hash, &shadows->mnt_hash);
865                 list_add(&mnt->mnt_child, &shadows->mnt_child);
866         } else {
867                 hlist_add_head_rcu(&mnt->mnt_hash,
868                                 m_hash(&parent->mnt, mnt->mnt_mountpoint));
869                 list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
870         }
871 }
872 
873 /*
874  * vfsmount lock must be held for write
875  */
876 static void commit_tree(struct mount *mnt, struct mount *shadows)
877 {
878         struct mount *parent = mnt->mnt_parent;
879         struct mount *m;
880         LIST_HEAD(head);
881         struct mnt_namespace *n = parent->mnt_ns;
882 
883         BUG_ON(parent == mnt);
884 
885         list_add_tail(&head, &mnt->mnt_list);
886         list_for_each_entry(m, &head, mnt_list)
887                 m->mnt_ns = n;
888 
889         list_splice(&head, n->list.prev);
890 
891         attach_shadowed(mnt, parent, shadows);
892         touch_mnt_namespace(n);
893 }
894 
895 static struct mount *next_mnt(struct mount *p, struct mount *root)
896 {
897         struct list_head *next = p->mnt_mounts.next;
898         if (next == &p->mnt_mounts) {
899                 while (1) {
900                         if (p == root)
901                                 return NULL;
902                         next = p->mnt_child.next;
903                         if (next != &p->mnt_parent->mnt_mounts)
904                                 break;
905                         p = p->mnt_parent;
906                 }
907         }
908         return list_entry(next, struct mount, mnt_child);
909 }
910 
911 static struct mount *skip_mnt_tree(struct mount *p)
912 {
913         struct list_head *prev = p->mnt_mounts.prev;
914         while (prev != &p->mnt_mounts) {
915                 p = list_entry(prev, struct mount, mnt_child);
916                 prev = p->mnt_mounts.prev;
917         }
918         return p;
919 }
920 
921 struct vfsmount *
922 vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
923 {
924         struct mount *mnt;
925         struct dentry *root;
926 
927         if (!type)
928                 return ERR_PTR(-ENODEV);
929 
930         mnt = alloc_vfsmnt(name);
931         if (!mnt)
932                 return ERR_PTR(-ENOMEM);
933 
934         if (flags & MS_KERNMOUNT)
935                 mnt->mnt.mnt_flags = MNT_INTERNAL;
936 
937         root = mount_fs(type, flags, name, data);
938         if (IS_ERR(root)) {
939                 mnt_free_id(mnt);
940                 free_vfsmnt(mnt);
941                 return ERR_CAST(root);
942         }
943 
944         mnt->mnt.mnt_root = root;
945         mnt->mnt.mnt_sb = root->d_sb;
946         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
947         mnt->mnt_parent = mnt;
948         lock_mount_hash();
949         list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
950         unlock_mount_hash();
951         return &mnt->mnt;
952 }
953 EXPORT_SYMBOL_GPL(vfs_kern_mount);
954 
955 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
956                                         int flag)
957 {
958         struct super_block *sb = old->mnt.mnt_sb;
959         struct mount *mnt;
960         int err;
961 
962         mnt = alloc_vfsmnt(old->mnt_devname);
963         if (!mnt)
964                 return ERR_PTR(-ENOMEM);
965 
966         if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
967                 mnt->mnt_group_id = 0; /* not a peer of original */
968         else
969                 mnt->mnt_group_id = old->mnt_group_id;
970 
971         if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
972                 err = mnt_alloc_group_id(mnt);
973                 if (err)
974                         goto out_free;
975         }
976 
977         mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~(MNT_WRITE_HOLD|MNT_MARKED);
978         /* Don't allow unprivileged users to change mount flags */
979         if (flag & CL_UNPRIVILEGED) {
980                 mnt->mnt.mnt_flags |= MNT_LOCK_ATIME;
981 
982                 if (mnt->mnt.mnt_flags & MNT_READONLY)
983                         mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
984 
985                 if (mnt->mnt.mnt_flags & MNT_NODEV)
986                         mnt->mnt.mnt_flags |= MNT_LOCK_NODEV;
987 
988                 if (mnt->mnt.mnt_flags & MNT_NOSUID)
989                         mnt->mnt.mnt_flags |= MNT_LOCK_NOSUID;
990 
991                 if (mnt->mnt.mnt_flags & MNT_NOEXEC)
992                         mnt->mnt.mnt_flags |= MNT_LOCK_NOEXEC;
993         }
994 
995         /* Don't allow unprivileged users to reveal what is under a mount */
996         if ((flag & CL_UNPRIVILEGED) &&
997             (!(flag & CL_EXPIRE) || list_empty(&old->mnt_expire)))
998                 mnt->mnt.mnt_flags |= MNT_LOCKED;
999 
1000         atomic_inc(&sb->s_active);
1001         mnt->mnt.mnt_sb = sb;
1002         mnt->mnt.mnt_root = dget(root);
1003         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1004         mnt->mnt_parent = mnt;
1005         lock_mount_hash();
1006         list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
1007         unlock_mount_hash();
1008 
1009         if ((flag & CL_SLAVE) ||
1010             ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
1011                 list_add(&mnt->mnt_slave, &old->mnt_slave_list);
1012                 mnt->mnt_master = old;
1013                 CLEAR_MNT_SHARED(mnt);
1014         } else if (!(flag & CL_PRIVATE)) {
1015                 if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
1016                         list_add(&mnt->mnt_share, &old->mnt_share);
1017                 if (IS_MNT_SLAVE(old))
1018                         list_add(&mnt->mnt_slave, &old->mnt_slave);
1019                 mnt->mnt_master = old->mnt_master;
1020         }
1021         if (flag & CL_MAKE_SHARED)
1022                 set_mnt_shared(mnt);
1023 
1024         /* stick the duplicate mount on the same expiry list
1025          * as the original if that was on one */
1026         if (flag & CL_EXPIRE) {
1027                 if (!list_empty(&old->mnt_expire))
1028                         list_add(&mnt->mnt_expire, &old->mnt_expire);
1029         }
1030 
1031         return mnt;
1032 
1033  out_free:
1034         mnt_free_id(mnt);
1035         free_vfsmnt(mnt);
1036         return ERR_PTR(err);
1037 }
1038 
1039 static void cleanup_mnt(struct mount *mnt)
1040 {
1041         /*
1042          * This probably indicates that somebody messed
1043          * up a mnt_want/drop_write() pair.  If this
1044          * happens, the filesystem was probably unable
1045          * to make r/w->r/o transitions.
1046          */
1047         /*
1048          * The locking used to deal with mnt_count decrement provides barriers,
1049          * so mnt_get_writers() below is safe.
1050          */
1051         WARN_ON(mnt_get_writers(mnt));
1052         if (unlikely(mnt->mnt_pins.first))
1053                 mnt_pin_kill(mnt);
1054         fsnotify_vfsmount_delete(&mnt->mnt);
1055         dput(mnt->mnt.mnt_root);
1056         deactivate_super(mnt->mnt.mnt_sb);
1057         mnt_free_id(mnt);
1058         call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
1059 }
1060 
1061 static void __cleanup_mnt(struct rcu_head *head)
1062 {
1063         cleanup_mnt(container_of(head, struct mount, mnt_rcu));
1064 }
1065 
1066 static LLIST_HEAD(delayed_mntput_list);
1067 static void delayed_mntput(struct work_struct *unused)
1068 {
1069         struct llist_node *node = llist_del_all(&delayed_mntput_list);
1070         struct llist_node *next;
1071 
1072         for (; node; node = next) {
1073                 next = llist_next(node);
1074                 cleanup_mnt(llist_entry(node, struct mount, mnt_llist));
1075         }
1076 }
1077 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
1078 
1079 static void mntput_no_expire(struct mount *mnt)
1080 {
1081         rcu_read_lock();
1082         mnt_add_count(mnt, -1);
1083         if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
1084                 rcu_read_unlock();
1085                 return;
1086         }
1087         lock_mount_hash();
1088         if (mnt_get_count(mnt)) {
1089                 rcu_read_unlock();
1090                 unlock_mount_hash();
1091                 return;
1092         }
1093         if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
1094                 rcu_read_unlock();
1095                 unlock_mount_hash();
1096                 return;
1097         }
1098         mnt->mnt.mnt_flags |= MNT_DOOMED;
1099         rcu_read_unlock();
1100 
1101         list_del(&mnt->mnt_instance);
1102 
1103         if (unlikely(!list_empty(&mnt->mnt_mounts))) {
1104                 struct mount *p, *tmp;
1105                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
1106                         umount_mnt(p);
1107                 }
1108         }
1109         unlock_mount_hash();
1110 
1111         if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
1112                 struct task_struct *task = current;
1113                 if (likely(!(task->flags & PF_KTHREAD))) {
1114                         init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
1115                         if (!task_work_add(task, &mnt->mnt_rcu, true))
1116                                 return;
1117                 }
1118                 if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
1119                         schedule_delayed_work(&delayed_mntput_work, 1);
1120                 return;
1121         }
1122         cleanup_mnt(mnt);
1123 }
1124 
1125 void mntput(struct vfsmount *mnt)
1126 {
1127         if (mnt) {
1128                 struct mount *m = real_mount(mnt);
1129                 /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
1130                 if (unlikely(m->mnt_expiry_mark))
1131                         m->mnt_expiry_mark = 0;
1132                 mntput_no_expire(m);
1133         }
1134 }
1135 EXPORT_SYMBOL(mntput);
1136 
1137 struct vfsmount *mntget(struct vfsmount *mnt)
1138 {
1139         if (mnt)
1140                 mnt_add_count(real_mount(mnt), 1);
1141         return mnt;
1142 }
1143 EXPORT_SYMBOL(mntget);
1144 
1145 struct vfsmount *mnt_clone_internal(struct path *path)
1146 {
1147         struct mount *p;
1148         p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
1149         if (IS_ERR(p))
1150                 return ERR_CAST(p);
1151         p->mnt.mnt_flags |= MNT_INTERNAL;
1152         return &p->mnt;
1153 }
1154 
1155 static inline void mangle(struct seq_file *m, const char *s)
1156 {
1157         seq_escape(m, s, " \t\n\\");
1158 }
1159 
1160 /*
1161  * Simple .show_options callback for filesystems which don't want to
1162  * implement more complex mount option showing.
1163  *
1164  * See also save_mount_options().
1165  */
1166 int generic_show_options(struct seq_file *m, struct dentry *root)
1167 {
1168         const char *options;
1169 
1170         rcu_read_lock();
1171         options = rcu_dereference(root->d_sb->s_options);
1172 
1173         if (options != NULL && options[0]) {
1174                 seq_putc(m, ',');
1175                 mangle(m, options);
1176         }
1177         rcu_read_unlock();
1178 
1179         return 0;
1180 }
1181 EXPORT_SYMBOL(generic_show_options);
1182 
1183 /*
1184  * If filesystem uses generic_show_options(), this function should be
1185  * called from the fill_super() callback.
1186  *
1187  * The .remount_fs callback usually needs to be handled in a special
1188  * way, to make sure, that previous options are not overwritten if the
1189  * remount fails.
1190  *
1191  * Also note, that if the filesystem's .remount_fs function doesn't
1192  * reset all options to their default value, but changes only newly
1193  * given options, then the displayed options will not reflect reality
1194  * any more.
1195  */
1196 void save_mount_options(struct super_block *sb, char *options)
1197 {
1198         BUG_ON(sb->s_options);
1199         rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
1200 }
1201 EXPORT_SYMBOL(save_mount_options);
1202 
1203 void replace_mount_options(struct super_block *sb, char *options)
1204 {
1205         char *old = sb->s_options;
1206         rcu_assign_pointer(sb->s_options, options);
1207         if (old) {
1208                 synchronize_rcu();
1209                 kfree(old);
1210         }
1211 }
1212 EXPORT_SYMBOL(replace_mount_options);
1213 
1214 #ifdef CONFIG_PROC_FS
1215 /* iterator; we want it to have access to namespace_sem, thus here... */
1216 static void *m_start(struct seq_file *m, loff_t *pos)
1217 {
1218         struct proc_mounts *p = proc_mounts(m);
1219 
1220         down_read(&namespace_sem);
1221         if (p->cached_event == p->ns->event) {
1222                 void *v = p->cached_mount;
1223                 if (*pos == p->cached_index)
1224                         return v;
1225                 if (*pos == p->cached_index + 1) {
1226                         v = seq_list_next(v, &p->ns->list, &p->cached_index);
1227                         return p->cached_mount = v;
1228                 }
1229         }
1230 
1231         p->cached_event = p->ns->event;
1232         p->cached_mount = seq_list_start(&p->ns->list, *pos);
1233         p->cached_index = *pos;
1234         return p->cached_mount;
1235 }
1236 
1237 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1238 {
1239         struct proc_mounts *p = proc_mounts(m);
1240 
1241         p->cached_mount = seq_list_next(v, &p->ns->list, pos);
1242         p->cached_index = *pos;
1243         return p->cached_mount;
1244 }
1245 
1246 static void m_stop(struct seq_file *m, void *v)
1247 {
1248         up_read(&namespace_sem);
1249 }
1250 
1251 static int m_show(struct seq_file *m, void *v)
1252 {
1253         struct proc_mounts *p = proc_mounts(m);
1254         struct mount *r = list_entry(v, struct mount, mnt_list);
1255         return p->show(m, &r->mnt);
1256 }
1257 
1258 const struct seq_operations mounts_op = {
1259         .start  = m_start,
1260         .next   = m_next,
1261         .stop   = m_stop,
1262         .show   = m_show,
1263 };
1264 #endif  /* CONFIG_PROC_FS */
1265 
1266 /**
1267  * may_umount_tree - check if a mount tree is busy
1268  * @mnt: root of mount tree
1269  *
1270  * This is called to check if a tree of mounts has any
1271  * open files, pwds, chroots or sub mounts that are
1272  * busy.
1273  */
1274 int may_umount_tree(struct vfsmount *m)
1275 {
1276         struct mount *mnt = real_mount(m);
1277         int actual_refs = 0;
1278         int minimum_refs = 0;
1279         struct mount *p;
1280         BUG_ON(!m);
1281 
1282         /* write lock needed for mnt_get_count */
1283         lock_mount_hash();
1284         for (p = mnt; p; p = next_mnt(p, mnt)) {
1285                 actual_refs += mnt_get_count(p);
1286                 minimum_refs += 2;
1287         }
1288         unlock_mount_hash();
1289 
1290         if (actual_refs > minimum_refs)
1291                 return 0;
1292 
1293         return 1;
1294 }
1295 
1296 EXPORT_SYMBOL(may_umount_tree);
1297 
1298 /**
1299  * may_umount - check if a mount point is busy
1300  * @mnt: root of mount
1301  *
1302  * This is called to check if a mount point has any
1303  * open files, pwds, chroots or sub mounts. If the
1304  * mount has sub mounts this will return busy
1305  * regardless of whether the sub mounts are busy.
1306  *
1307  * Doesn't take quota and stuff into account. IOW, in some cases it will
1308  * give false negatives. The main reason why it's here is that we need
1309  * a non-destructive way to look for easily umountable filesystems.
1310  */
1311 int may_umount(struct vfsmount *mnt)
1312 {
1313         int ret = 1;
1314         down_read(&namespace_sem);
1315         lock_mount_hash();
1316         if (propagate_mount_busy(real_mount(mnt), 2))
1317                 ret = 0;
1318         unlock_mount_hash();
1319         up_read(&namespace_sem);
1320         return ret;
1321 }
1322 
1323 EXPORT_SYMBOL(may_umount);
1324 
1325 static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
1326 
1327 static void namespace_unlock(void)
1328 {
1329         struct hlist_head head = unmounted;
1330 
1331         if (likely(hlist_empty(&head))) {
1332                 up_write(&namespace_sem);
1333                 return;
1334         }
1335 
1336         head.first->pprev = &head.first;
1337         INIT_HLIST_HEAD(&unmounted);
1338         up_write(&namespace_sem);
1339 
1340         synchronize_rcu();
1341 
1342         group_pin_kill(&head);
1343 }
1344 
1345 static inline void namespace_lock(void)
1346 {
1347         down_write(&namespace_sem);
1348 }
1349 
1350 enum umount_tree_flags {
1351         UMOUNT_SYNC = 1,
1352         UMOUNT_PROPAGATE = 2,
1353         UMOUNT_CONNECTED = 4,
1354 };
1355 /*
1356  * mount_lock must be held
1357  * namespace_sem must be held for write
1358  */
1359 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
1360 {
1361         LIST_HEAD(tmp_list);
1362         struct mount *p;
1363 
1364         if (how & UMOUNT_PROPAGATE)
1365                 propagate_mount_unlock(mnt);
1366 
1367         /* Gather the mounts to umount */
1368         for (p = mnt; p; p = next_mnt(p, mnt)) {
1369                 p->mnt.mnt_flags |= MNT_UMOUNT;
1370                 list_move(&p->mnt_list, &tmp_list);
1371         }
1372 
1373         /* Hide the mounts from mnt_mounts */
1374         list_for_each_entry(p, &tmp_list, mnt_list) {
1375                 list_del_init(&p->mnt_child);
1376         }
1377 
1378         /* Add propogated mounts to the tmp_list */
1379         if (how & UMOUNT_PROPAGATE)
1380                 propagate_umount(&tmp_list);
1381 
1382         while (!list_empty(&tmp_list)) {
1383                 bool disconnect;
1384                 p = list_first_entry(&tmp_list, struct mount, mnt_list);
1385                 list_del_init(&p->mnt_expire);
1386                 list_del_init(&p->mnt_list);
1387                 __touch_mnt_namespace(p->mnt_ns);
1388                 p->mnt_ns = NULL;
1389                 if (how & UMOUNT_SYNC)
1390                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
1391 
1392                 disconnect = !(((how & UMOUNT_CONNECTED) &&
1393                                 mnt_has_parent(p) &&
1394                                 (p->mnt_parent->mnt.mnt_flags & MNT_UMOUNT)) ||
1395                                IS_MNT_LOCKED_AND_LAZY(p));
1396 
1397                 pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
1398                                  disconnect ? &unmounted : NULL);
1399                 if (mnt_has_parent(p)) {
1400                         mnt_add_count(p->mnt_parent, -1);
1401                         if (!disconnect) {
1402                                 /* Don't forget about p */
1403                                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
1404                         } else {
1405                                 umount_mnt(p);
1406                         }
1407                 }
1408                 change_mnt_propagation(p, MS_PRIVATE);
1409         }
1410 }
1411 
1412 static void shrink_submounts(struct mount *mnt);
1413 
1414 static int do_umount(struct mount *mnt, int flags)
1415 {
1416         struct super_block *sb = mnt->mnt.mnt_sb;
1417         int retval;
1418 
1419         retval = security_sb_umount(&mnt->mnt, flags);
1420         if (retval)
1421                 return retval;
1422 
1423         /*
1424          * Allow userspace to request a mountpoint be expired rather than
1425          * unmounting unconditionally. Unmount only happens if:
1426          *  (1) the mark is already set (the mark is cleared by mntput())
1427          *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1428          */
1429         if (flags & MNT_EXPIRE) {
1430                 if (&mnt->mnt == current->fs->root.mnt ||
1431                     flags & (MNT_FORCE | MNT_DETACH))
1432                         return -EINVAL;
1433 
1434                 /*
1435                  * probably don't strictly need the lock here if we examined
1436                  * all race cases, but it's a slowpath.
1437                  */
1438                 lock_mount_hash();
1439                 if (mnt_get_count(mnt) != 2) {
1440                         unlock_mount_hash();
1441                         return -EBUSY;
1442                 }
1443                 unlock_mount_hash();
1444 
1445                 if (!xchg(&mnt->mnt_expiry_mark, 1))
1446                         return -EAGAIN;
1447         }
1448 
1449         /*
1450          * If we may have to abort operations to get out of this
1451          * mount, and they will themselves hold resources we must
1452          * allow the fs to do things. In the Unix tradition of
1453          * 'Gee thats tricky lets do it in userspace' the umount_begin
1454          * might fail to complete on the first run through as other tasks
1455          * must return, and the like. Thats for the mount program to worry
1456          * about for the moment.
1457          */
1458 
1459         if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1460                 sb->s_op->umount_begin(sb);
1461         }
1462 
1463         /*
1464          * No sense to grab the lock for this test, but test itself looks
1465          * somewhat bogus. Suggestions for better replacement?
1466          * Ho-hum... In principle, we might treat that as umount + switch
1467          * to rootfs. GC would eventually take care of the old vfsmount.
1468          * Actually it makes sense, especially if rootfs would contain a
1469          * /reboot - static binary that would close all descriptors and
1470          * call reboot(9). Then init(8) could umount root and exec /reboot.
1471          */
1472         if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1473                 /*
1474                  * Special case for "unmounting" root ...
1475                  * we just try to remount it readonly.
1476                  */
1477                 if (!capable(CAP_SYS_ADMIN))
1478                         return -EPERM;
1479                 down_write(&sb->s_umount);
1480                 if (!(sb->s_flags & MS_RDONLY))
1481                         retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1482                 up_write(&sb->s_umount);
1483                 return retval;
1484         }
1485 
1486         namespace_lock();
1487         lock_mount_hash();
1488         event++;
1489 
1490         if (flags & MNT_DETACH) {
1491                 if (!list_empty(&mnt->mnt_list))
1492                         umount_tree(mnt, UMOUNT_PROPAGATE);
1493                 retval = 0;
1494         } else {
1495                 shrink_submounts(mnt);
1496                 retval = -EBUSY;
1497                 if (!propagate_mount_busy(mnt, 2)) {
1498                         if (!list_empty(&mnt->mnt_list))
1499                                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
1500                         retval = 0;
1501                 }
1502         }
1503         unlock_mount_hash();
1504         namespace_unlock();
1505         return retval;
1506 }
1507 
1508 /*
1509  * __detach_mounts - lazily unmount all mounts on the specified dentry
1510  *
1511  * During unlink, rmdir, and d_drop it is possible to loose the path
1512  * to an existing mountpoint, and wind up leaking the mount.
1513  * detach_mounts allows lazily unmounting those mounts instead of
1514  * leaking them.
1515  *
1516  * The caller may hold dentry->d_inode->i_mutex.
1517  */
1518 void __detach_mounts(struct dentry *dentry)
1519 {
1520         struct mountpoint *mp;
1521         struct mount *mnt;
1522 
1523         namespace_lock();
1524         mp = lookup_mountpoint(dentry);
1525         if (IS_ERR_OR_NULL(mp))
1526                 goto out_unlock;
1527 
1528         lock_mount_hash();
1529         while (!hlist_empty(&mp->m_list)) {
1530                 mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
1531                 if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
1532                         struct mount *p, *tmp;
1533                         list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
1534                                 hlist_add_head(&p->mnt_umount.s_list, &unmounted);
1535                                 umount_mnt(p);
1536                         }
1537                 }
1538                 else umount_tree(mnt, UMOUNT_CONNECTED);
1539         }
1540         unlock_mount_hash();
1541         put_mountpoint(mp);
1542 out_unlock:
1543         namespace_unlock();
1544 }
1545 
1546 /* 
1547  * Is the caller allowed to modify his namespace?
1548  */
1549 static inline bool may_mount(void)
1550 {
1551         return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1552 }
1553 
1554 /*
1555  * Now umount can handle mount points as well as block devices.
1556  * This is important for filesystems which use unnamed block devices.
1557  *
1558  * We now support a flag for forced unmount like the other 'big iron'
1559  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1560  */
1561 
1562 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1563 {
1564         struct path path;
1565         struct mount *mnt;
1566         int retval;
1567         int lookup_flags = 0;
1568 
1569         if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1570                 return -EINVAL;
1571 
1572         if (!may_mount())
1573                 return -EPERM;
1574 
1575         if (!(flags & UMOUNT_NOFOLLOW))
1576                 lookup_flags |= LOOKUP_FOLLOW;
1577 
1578         retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
1579         if (retval)
1580                 goto out;
1581         mnt = real_mount(path.mnt);
1582         retval = -EINVAL;
1583         if (path.dentry != path.mnt->mnt_root)
1584                 goto dput_and_out;
1585         if (!check_mnt(mnt))
1586                 goto dput_and_out;
1587         if (mnt->mnt.mnt_flags & MNT_LOCKED)
1588                 goto dput_and_out;
1589         retval = -EPERM;
1590         if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
1591                 goto dput_and_out;
1592 
1593         retval = do_umount(mnt, flags);
1594 dput_and_out:
1595         /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1596         dput(path.dentry);
1597         mntput_no_expire(mnt);
1598 out:
1599         return retval;
1600 }
1601 
1602 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
1603 
1604 /*
1605  *      The 2.0 compatible umount. No flags.
1606  */
1607 SYSCALL_DEFINE1(oldumount, char __user *, name)
1608 {
1609         return sys_umount(name, 0);
1610 }
1611 
1612 #endif
1613 
1614 static bool is_mnt_ns_file(struct dentry *dentry)
1615 {
1616         /* Is this a proxy for a mount namespace? */
1617         return dentry->d_op == &ns_dentry_operations &&
1618                dentry->d_fsdata == &mntns_operations;
1619 }
1620 
1621 struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
1622 {
1623         return container_of(ns, struct mnt_namespace, ns);
1624 }
1625 
1626 static bool mnt_ns_loop(struct dentry *dentry)
1627 {
1628         /* Could bind mounting the mount namespace inode cause a
1629          * mount namespace loop?
1630          */
1631         struct mnt_namespace *mnt_ns;
1632         if (!is_mnt_ns_file(dentry))
1633                 return false;
1634 
1635         mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
1636         return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1637 }
1638 
1639 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1640                                         int flag)
1641 {
1642         struct mount *res, *p, *q, *r, *parent;
1643 
1644         if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
1645                 return ERR_PTR(-EINVAL);
1646 
1647         if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
1648                 return ERR_PTR(-EINVAL);
1649 
1650         res = q = clone_mnt(mnt, dentry, flag);
1651         if (IS_ERR(q))
1652                 return q;
1653 
1654         q->mnt_mountpoint = mnt->mnt_mountpoint;
1655 
1656         p = mnt;
1657         list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1658                 struct mount *s;
1659                 if (!is_subdir(r->mnt_mountpoint, dentry))
1660                         continue;
1661 
1662                 for (s = r; s; s = next_mnt(s, r)) {
1663                         struct mount *t = NULL;
1664                         if (!(flag & CL_COPY_UNBINDABLE) &&
1665                             IS_MNT_UNBINDABLE(s)) {
1666                                 s = skip_mnt_tree(s);
1667                                 continue;
1668                         }
1669                         if (!(flag & CL_COPY_MNT_NS_FILE) &&
1670                             is_mnt_ns_file(s->mnt.mnt_root)) {
1671                                 s = skip_mnt_tree(s);
1672                                 continue;
1673                         }
1674                         while (p != s->mnt_parent) {
1675                                 p = p->mnt_parent;
1676                                 q = q->mnt_parent;
1677                         }
1678                         p = s;
1679                         parent = q;
1680                         q = clone_mnt(p, p->mnt.mnt_root, flag);
1681                         if (IS_ERR(q))
1682                                 goto out;
1683                         lock_mount_hash();
1684                         list_add_tail(&q->mnt_list, &res->mnt_list);
1685                         mnt_set_mountpoint(parent, p->mnt_mp, q);
1686                         if (!list_empty(&parent->mnt_mounts)) {
1687                                 t = list_last_entry(&parent->mnt_mounts,
1688                                         struct mount, mnt_child);
1689                                 if (t->mnt_mp != p->mnt_mp)
1690                                         t = NULL;
1691                         }
1692                         attach_shadowed(q, parent, t);
1693                         unlock_mount_hash();
1694                 }
1695         }
1696         return res;
1697 out:
1698         if (res) {
1699                 lock_mount_hash();
1700                 umount_tree(res, UMOUNT_SYNC);
1701                 unlock_mount_hash();
1702         }
1703         return q;
1704 }
1705 
1706 /* Caller should check returned pointer for errors */
1707 
1708 struct vfsmount *collect_mounts(struct path *path)
1709 {
1710         struct mount *tree;
1711         namespace_lock();
1712         if (!check_mnt(real_mount(path->mnt)))
1713                 tree = ERR_PTR(-EINVAL);
1714         else
1715                 tree = copy_tree(real_mount(path->mnt), path->dentry,
1716                                  CL_COPY_ALL | CL_PRIVATE);
1717         namespace_unlock();
1718         if (IS_ERR(tree))
1719                 return ERR_CAST(tree);
1720         return &tree->mnt;
1721 }
1722 
1723 void drop_collected_mounts(struct vfsmount *mnt)
1724 {
1725         namespace_lock();
1726         lock_mount_hash();
1727         umount_tree(real_mount(mnt), UMOUNT_SYNC);
1728         unlock_mount_hash();
1729         namespace_unlock();
1730 }
1731 
1732 /**
1733  * clone_private_mount - create a private clone of a path
1734  *
1735  * This creates a new vfsmount, which will be the clone of @path.  The new will
1736  * not be attached anywhere in the namespace and will be private (i.e. changes
1737  * to the originating mount won't be propagated into this).
1738  *
1739  * Release with mntput().
1740  */
1741 struct vfsmount *clone_private_mount(struct path *path)
1742 {
1743         struct mount *old_mnt = real_mount(path->mnt);
1744         struct mount *new_mnt;
1745 
1746         if (IS_MNT_UNBINDABLE(old_mnt))
1747                 return ERR_PTR(-EINVAL);
1748 
1749         down_read(&namespace_sem);
1750         new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
1751         up_read(&namespace_sem);
1752         if (IS_ERR(new_mnt))
1753                 return ERR_CAST(new_mnt);
1754 
1755         return &new_mnt->mnt;
1756 }
1757 EXPORT_SYMBOL_GPL(clone_private_mount);
1758 
1759 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1760                    struct vfsmount *root)
1761 {
1762         struct mount *mnt;
1763         int res = f(root, arg);
1764         if (res)
1765                 return res;
1766         list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
1767                 res = f(&mnt->mnt, arg);
1768                 if (res)
1769                         return res;
1770         }
1771         return 0;
1772 }
1773 
1774 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
1775 {
1776         struct mount *p;
1777 
1778         for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1779                 if (p->mnt_group_id && !IS_MNT_SHARED(p))
1780                         mnt_release_group_id(p);
1781         }
1782 }
1783 
1784 static int invent_group_ids(struct mount *mnt, bool recurse)
1785 {
1786         struct mount *p;
1787 
1788         for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1789                 if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1790                         int err = mnt_alloc_group_id(p);
1791                         if (err) {
1792                                 cleanup_group_ids(mnt, p);
1793                                 return err;
1794                         }
1795                 }
1796         }
1797 
1798         return 0;
1799 }
1800 
1801 /*
1802  *  @source_mnt : mount tree to be attached
1803  *  @nd         : place the mount tree @source_mnt is attached
1804  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1805  *                 store the parent mount and mountpoint dentry.
1806  *                 (done when source_mnt is moved)
1807  *
1808  *  NOTE: in the table below explains the semantics when a source mount
1809  *  of a given type is attached to a destination mount of a given type.
1810  * ---------------------------------------------------------------------------
1811  * |         BIND MOUNT OPERATION                                            |
1812  * |**************************************************************************
1813  * | source-->| shared        |       private  |       slave    | unbindable |
1814  * | dest     |               |                |                |            |
1815  * |   |      |               |                |                |            |
1816  * |   v      |               |                |                |            |
1817  * |**************************************************************************
1818  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1819  * |          |               |                |                |            |
1820  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1821  * ***************************************************************************
1822  * A bind operation clones the source mount and mounts the clone on the
1823  * destination mount.
1824  *
1825  * (++)  the cloned mount is propagated to all the mounts in the propagation
1826  *       tree of the destination mount and the cloned mount is added to
1827  *       the peer group of the source mount.
1828  * (+)   the cloned mount is created under the destination mount and is marked
1829  *       as shared. The cloned mount is added to the peer group of the source
1830  *       mount.
1831  * (+++) the mount is propagated to all the mounts in the propagation tree
1832  *       of the destination mount and the cloned mount is made slave
1833  *       of the same master as that of the source mount. The cloned mount
1834  *       is marked as 'shared and slave'.
1835  * (*)   the cloned mount is made a slave of the same master as that of the
1836  *       source mount.
1837  *
1838  * ---------------------------------------------------------------------------
1839  * |                    MOVE MOUNT OPERATION                                 |
1840  * |**************************************************************************
1841  * | source-->| shared        |       private  |       slave    | unbindable |
1842  * | dest     |               |                |                |            |
1843  * |   |      |               |                |                |            |
1844  * |   v      |               |                |                |            |
1845  * |**************************************************************************
1846  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
1847  * |          |               |                |                |            |
1848  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
1849  * ***************************************************************************
1850  *
1851  * (+)  the mount is moved to the destination. And is then propagated to
1852  *      all the mounts in the propagation tree of the destination mount.
1853  * (+*)  the mount is moved to the destination.
1854  * (+++)  the mount is moved to the destination and is then propagated to
1855  *      all the mounts belonging to the destination mount's propagation tree.
1856  *      the mount is marked as 'shared and slave'.
1857  * (*)  the mount continues to be a slave at the new location.
1858  *
1859  * if the source mount is a tree, the operations explained above is
1860  * applied to each mount in the tree.
1861  * Must be called without spinlocks held, since this function can sleep
1862  * in allocations.
1863  */
1864 static int attach_recursive_mnt(struct mount *source_mnt,
1865                         struct mount *dest_mnt,
1866                         struct mountpoint *dest_mp,
1867                         struct path *parent_path)
1868 {
1869         HLIST_HEAD(tree_list);
1870         struct mount *child, *p;
1871         struct hlist_node *n;
1872         int err;
1873 
1874         if (IS_MNT_SHARED(dest_mnt)) {
1875                 err = invent_group_ids(source_mnt, true);
1876                 if (err)
1877                         goto out;
1878                 err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
1879                 lock_mount_hash();
1880                 if (err)
1881                         goto out_cleanup_ids;
1882                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
1883                         set_mnt_shared(p);
1884         } else {
1885                 lock_mount_hash();
1886         }
1887         if (parent_path) {
1888                 detach_mnt(source_mnt, parent_path);
1889                 attach_mnt(source_mnt, dest_mnt, dest_mp);
1890                 touch_mnt_namespace(source_mnt->mnt_ns);
1891         } else {
1892                 mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
1893                 commit_tree(source_mnt, NULL);
1894         }
1895 
1896         hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
1897                 struct mount *q;
1898                 hlist_del_init(&child->mnt_hash);
1899                 q = __lookup_mnt_last(&child->mnt_parent->mnt,
1900                                       child->mnt_mountpoint);
1901                 commit_tree(child, q);
1902         }
1903         unlock_mount_hash();
1904 
1905         return 0;
1906 
1907  out_cleanup_ids:
1908         while (!hlist_empty(&tree_list)) {
1909                 child = hlist_entry(tree_list.first, struct mount, mnt_hash);
1910                 umount_tree(child, UMOUNT_SYNC);
1911         }
1912         unlock_mount_hash();
1913         cleanup_group_ids(source_mnt, NULL);
1914  out:
1915         return err;
1916 }
1917 
1918 static struct mountpoint *lock_mount(struct path *path)
1919 {
1920         struct vfsmount *mnt;
1921         struct dentry *dentry = path->dentry;
1922 retry:
1923         mutex_lock(&dentry->d_inode->i_mutex);
1924         if (unlikely(cant_mount(dentry))) {
1925                 mutex_unlock(&dentry->d_inode->i_mutex);
1926                 return ERR_PTR(-ENOENT);
1927         }
1928         namespace_lock();
1929         mnt = lookup_mnt(path);
1930         if (likely(!mnt)) {
1931                 struct mountpoint *mp = lookup_mountpoint(dentry);
1932                 if (!mp)
1933                         mp = new_mountpoint(dentry);
1934                 if (IS_ERR(mp)) {
1935                         namespace_unlock();
1936                         mutex_unlock(&dentry->d_inode->i_mutex);
1937                         return mp;
1938                 }
1939                 return mp;
1940         }
1941         namespace_unlock();
1942         mutex_unlock(&path->dentry->d_inode->i_mutex);
1943         path_put(path);
1944         path->mnt = mnt;
1945         dentry = path->dentry = dget(mnt->mnt_root);
1946         goto retry;
1947 }
1948 
1949 static void unlock_mount(struct mountpoint *where)
1950 {
1951         struct dentry *dentry = where->m_dentry;
1952         put_mountpoint(where);
1953         namespace_unlock();
1954         mutex_unlock(&dentry->d_inode->i_mutex);
1955 }
1956 
1957 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
1958 {
1959         if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
1960                 return -EINVAL;
1961 
1962         if (d_is_dir(mp->m_dentry) !=
1963               d_is_dir(mnt->mnt.mnt_root))
1964                 return -ENOTDIR;
1965 
1966         return attach_recursive_mnt(mnt, p, mp, NULL);
1967 }
1968 
1969 /*
1970  * Sanity check the flags to change_mnt_propagation.
1971  */
1972 
1973 static int flags_to_propagation_type(int flags)
1974 {
1975         int type = flags & ~(MS_REC | MS_SILENT);
1976 
1977         /* Fail if any non-propagation flags are set */
1978         if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1979                 return 0;
1980         /* Only one propagation flag should be set */
1981         if (!is_power_of_2(type))
1982                 return 0;
1983         return type;
1984 }
1985 
1986 /*
1987  * recursively change the type of the mountpoint.
1988  */
1989 static int do_change_type(struct path *path, int flag)
1990 {
1991         struct mount *m;
1992         struct mount *mnt = real_mount(path->mnt);
1993         int recurse = flag & MS_REC;
1994         int type;
1995         int err = 0;
1996 
1997         if (path->dentry != path->mnt->mnt_root)
1998                 return -EINVAL;
1999 
2000         type = flags_to_propagation_type(flag);
2001         if (!type)
2002                 return -EINVAL;
2003 
2004         namespace_lock();
2005         if (type == MS_SHARED) {
2006                 err = invent_group_ids(mnt, recurse);
2007                 if (err)
2008                         goto out_unlock;
2009         }
2010 
2011         lock_mount_hash();
2012         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
2013                 change_mnt_propagation(m, type);
2014         unlock_mount_hash();
2015 
2016  out_unlock:
2017         namespace_unlock();
2018         return err;
2019 }
2020 
2021 static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
2022 {
2023         struct mount *child;
2024         list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
2025                 if (!is_subdir(child->mnt_mountpoint, dentry))
2026                         continue;
2027 
2028                 if (child->mnt.mnt_flags & MNT_LOCKED)
2029                         return true;
2030         }
2031         return false;
2032 }
2033 
2034 /*
2035  * do loopback mount.
2036  */
2037 static int do_loopback(struct path *path, const char *old_name,
2038                                 int recurse)
2039 {
2040         struct path old_path;
2041         struct mount *mnt = NULL, *old, *parent;
2042         struct mountpoint *mp;
2043         int err;
2044         if (!old_name || !*old_name)
2045                 return -EINVAL;
2046         err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
2047         if (err)
2048                 return err;
2049 
2050         err = -EINVAL;
2051         if (mnt_ns_loop(old_path.dentry))
2052                 goto out; 
2053 
2054         mp = lock_mount(path);
2055         err = PTR_ERR(mp);
2056         if (IS_ERR(mp))
2057                 goto out;
2058 
2059         old = real_mount(old_path.mnt);
2060         parent = real_mount(path->mnt);
2061 
2062         err = -EINVAL;
2063         if (IS_MNT_UNBINDABLE(old))
2064                 goto out2;
2065 
2066         if (!check_mnt(parent))
2067                 goto out2;
2068 
2069         if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations)
2070                 goto out2;
2071 
2072         if (!recurse && has_locked_children(old, old_path.dentry))
2073                 goto out2;
2074 
2075         if (recurse)
2076                 mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
2077         else
2078                 mnt = clone_mnt(old, old_path.dentry, 0);
2079 
2080         if (IS_ERR(mnt)) {
2081                 err = PTR_ERR(mnt);
2082                 goto out2;
2083         }
2084 
2085         mnt->mnt.mnt_flags &= ~MNT_LOCKED;
2086 
2087         err = graft_tree(mnt, parent, mp);
2088         if (err) {
2089                 lock_mount_hash();
2090                 umount_tree(mnt, UMOUNT_SYNC);
2091                 unlock_mount_hash();
2092         }
2093 out2:
2094         unlock_mount(mp);
2095 out:
2096         path_put(&old_path);
2097         return err;
2098 }
2099 
2100 static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
2101 {
2102         int error = 0;
2103         int readonly_request = 0;
2104 
2105         if (ms_flags & MS_RDONLY)
2106                 readonly_request = 1;
2107         if (readonly_request == __mnt_is_readonly(mnt))
2108                 return 0;
2109 
2110         if (readonly_request)
2111                 error = mnt_make_readonly(real_mount(mnt));
2112         else
2113                 __mnt_unmake_readonly(real_mount(mnt));
2114         return error;
2115 }
2116 
2117 /*
2118  * change filesystem flags. dir should be a physical root of filesystem.
2119  * If you've mounted a non-root directory somewhere and want to do remount
2120  * on it - tough luck.
2121  */
2122 static int do_remount(struct path *path, int flags, int mnt_flags,
2123                       void *data)
2124 {
2125         int err;
2126         struct super_block *sb = path->mnt->mnt_sb;
2127         struct mount *mnt = real_mount(path->mnt);
2128 
2129         if (!check_mnt(mnt))
2130                 return -EINVAL;
2131 
2132         if (path->dentry != path->mnt->mnt_root)
2133                 return -EINVAL;
2134 
2135         /* Don't allow changing of locked mnt flags.
2136          *
2137          * No locks need to be held here while testing the various
2138          * MNT_LOCK flags because those flags can never be cleared
2139          * once they are set.
2140          */
2141         if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
2142             !(mnt_flags & MNT_READONLY)) {
2143                 return -EPERM;
2144         }
2145         if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
2146             !(mnt_flags & MNT_NODEV)) {
2147                 /* Was the nodev implicitly added in mount? */
2148                 if ((mnt->mnt_ns->user_ns != &init_user_ns) &&
2149                     !(sb->s_type->fs_flags & FS_USERNS_DEV_MOUNT)) {
2150                         mnt_flags |= MNT_NODEV;
2151                 } else {
2152                         return -EPERM;
2153                 }
2154         }
2155         if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&
2156             !(mnt_flags & MNT_NOSUID)) {
2157                 return -EPERM;
2158         }
2159         if ((mnt->mnt.mnt_flags & MNT_LOCK_NOEXEC) &&
2160             !(mnt_flags & MNT_NOEXEC)) {
2161                 return -EPERM;
2162         }
2163         if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
2164             ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK))) {
2165                 return -EPERM;
2166         }
2167 
2168         err = security_sb_remount(sb, data);
2169         if (err)
2170                 return err;
2171 
2172         down_write(&sb->s_umount);
2173         if (flags & MS_BIND)
2174                 err = change_mount_flags(path->mnt, flags);
2175         else if (!capable(CAP_SYS_ADMIN))
2176                 err = -EPERM;
2177         else
2178                 err = do_remount_sb(sb, flags, data, 0);
2179         if (!err) {
2180                 lock_mount_hash();
2181                 mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
2182                 mnt->mnt.mnt_flags = mnt_flags;
2183                 touch_mnt_namespace(mnt->mnt_ns);
2184                 unlock_mount_hash();
2185         }
2186         up_write(&sb->s_umount);
2187         return err;
2188 }
2189 
2190 static inline int tree_contains_unbindable(struct mount *mnt)
2191 {
2192         struct mount *p;
2193         for (p = mnt; p; p = next_mnt(p, mnt)) {
2194                 if (IS_MNT_UNBINDABLE(p))
2195                         return 1;
2196         }
2197         return 0;
2198 }
2199 
2200 static int do_move_mount(struct path *path, const char *old_name)
2201 {
2202         struct path old_path, parent_path;
2203         struct mount *p;
2204         struct mount *old;
2205         struct mountpoint *mp;
2206         int err;
2207         if (!old_name || !*old_name)
2208                 return -EINVAL;
2209         err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
2210         if (err)
2211                 return err;
2212 
2213         mp = lock_mount(path);
2214         err = PTR_ERR(mp);
2215         if (IS_ERR(mp))
2216                 goto out;
2217 
2218         old = real_mount(old_path.mnt);
2219         p = real_mount(path->mnt);
2220 
2221         err = -EINVAL;
2222         if (!check_mnt(p) || !check_mnt(old))
2223                 goto out1;
2224 
2225         if (old->mnt.mnt_flags & MNT_LOCKED)
2226                 goto out1;
2227 
2228         err = -EINVAL;
2229         if (old_path.dentry != old_path.mnt->mnt_root)
2230                 goto out1;
2231 
2232         if (!mnt_has_parent(old))
2233                 goto out1;
2234 
2235         if (d_is_dir(path->dentry) !=
2236               d_is_dir(old_path.dentry))
2237                 goto out1;
2238         /*
2239          * Don't move a mount residing in a shared parent.
2240          */
2241         if (IS_MNT_SHARED(old->mnt_parent))
2242                 goto out1;
2243         /*
2244          * Don't move a mount tree containing unbindable mounts to a destination
2245          * mount which is shared.
2246          */
2247         if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
2248                 goto out1;
2249         err = -ELOOP;
2250         for (; mnt_has_parent(p); p = p->mnt_parent)
2251                 if (p == old)
2252                         goto out1;
2253 
2254         err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
2255         if (err)
2256                 goto out1;
2257 
2258         /* if the mount is moved, it should no longer be expire
2259          * automatically */
2260         list_del_init(&old->mnt_expire);
2261 out1:
2262         unlock_mount(mp);
2263 out:
2264         if (!err)
2265                 path_put(&parent_path);
2266         path_put(&old_path);
2267         return err;
2268 }
2269 
2270 static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
2271 {
2272         int err;
2273         const char *subtype = strchr(fstype, '.');
2274         if (subtype) {
2275                 subtype++;
2276                 err = -EINVAL;
2277                 if (!subtype[0])
2278                         goto err;
2279         } else
2280                 subtype = "";
2281 
2282         mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
2283         err = -ENOMEM;
2284         if (!mnt->mnt_sb->s_subtype)
2285                 goto err;
2286         return mnt;
2287 
2288  err:
2289         mntput(mnt);
2290         return ERR_PTR(err);
2291 }
2292 
2293 /*
2294  * add a mount into a namespace's mount tree
2295  */
2296 static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
2297 {
2298         struct mountpoint *mp;
2299         struct mount *parent;
2300         int err;
2301 
2302         mnt_flags &= ~MNT_INTERNAL_FLAGS;
2303 
2304         mp = lock_mount(path);
2305         if (IS_ERR(mp))
2306                 return PTR_ERR(mp);
2307 
2308         parent = real_mount(path->mnt);
2309         err = -EINVAL;
2310         if (unlikely(!check_mnt(parent))) {
2311                 /* that's acceptable only for automounts done in private ns */
2312                 if (!(mnt_flags & MNT_SHRINKABLE))
2313                         goto unlock;
2314                 /* ... and for those we'd better have mountpoint still alive */
2315                 if (!parent->mnt_ns)
2316                         goto unlock;
2317         }
2318 
2319         /* Refuse the same filesystem on the same mount point */
2320         err = -EBUSY;
2321         if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
2322             path->mnt->mnt_root == path->dentry)
2323                 goto unlock;
2324 
2325         err = -EINVAL;
2326         if (d_is_symlink(newmnt->mnt.mnt_root))
2327                 goto unlock;
2328 
2329         newmnt->mnt.mnt_flags = mnt_flags;
2330         err = graft_tree(newmnt, parent, mp);
2331 
2332 unlock:
2333         unlock_mount(mp);
2334         return err;
2335 }
2336 
2337 static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
2338 
2339 /*
2340  * create a new mount for userspace and request it to be added into the
2341  * namespace's tree
2342  */
2343 static int do_new_mount(struct path *path, const char *fstype, int flags,
2344                         int mnt_flags, const char *name, void *data)
2345 {
2346         struct file_system_type *type;
2347         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2348         struct vfsmount *mnt;
2349         int err;
2350 
2351         if (!fstype)
2352                 return -EINVAL;
2353 
2354         type = get_fs_type(fstype);
2355         if (!type)
2356                 return -ENODEV;
2357 
2358         if (user_ns != &init_user_ns) {
2359                 if (!(type->fs_flags & FS_USERNS_MOUNT)) {
2360                         put_filesystem(type);
2361                         return -EPERM;
2362                 }
2363                 /* Only in special cases allow devices from mounts
2364                  * created outside the initial user namespace.
2365                  */
2366                 if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
2367                         flags |= MS_NODEV;
2368                         mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
2369                 }
2370                 if (type->fs_flags & FS_USERNS_VISIBLE) {
2371                         if (!fs_fully_visible(type, &mnt_flags))
2372                                 return -EPERM;
2373                 }
2374         }
2375 
2376         mnt = vfs_kern_mount(type, flags, name, data);
2377         if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
2378             !mnt->mnt_sb->s_subtype)
2379                 mnt = fs_set_subtype(mnt, fstype);
2380 
2381         put_filesystem(type);
2382         if (IS_ERR(mnt))
2383                 return PTR_ERR(mnt);
2384 
2385         err = do_add_mount(real_mount(mnt), path, mnt_flags);
2386         if (err)
2387                 mntput(mnt);
2388         return err;
2389 }
2390 
2391 int finish_automount(struct vfsmount *m, struct path *path)
2392 {
2393         struct mount *mnt = real_mount(m);
2394         int err;
2395         /* The new mount record should have at least 2 refs to prevent it being
2396          * expired before we get a chance to add it
2397          */
2398         BUG_ON(mnt_get_count(mnt) < 2);
2399 
2400         if (m->mnt_sb == path->mnt->mnt_sb &&
2401             m->mnt_root == path->dentry) {
2402                 err = -ELOOP;
2403                 goto fail;
2404         }
2405 
2406         err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2407         if (!err)
2408                 return 0;
2409 fail:
2410         /* remove m from any expiration list it may be on */
2411         if (!list_empty(&mnt->mnt_expire)) {
2412                 namespace_lock();
2413                 list_del_init(&mnt->mnt_expire);
2414                 namespace_unlock();
2415         }
2416         mntput(m);
2417         mntput(m);
2418         return err;
2419 }
2420 
2421 /**
2422  * mnt_set_expiry - Put a mount on an expiration list
2423  * @mnt: The mount to list.
2424  * @expiry_list: The list to add the mount to.
2425  */
2426 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2427 {
2428         namespace_lock();
2429 
2430         list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
2431 
2432         namespace_unlock();
2433 }
2434 EXPORT_SYMBOL(mnt_set_expiry);
2435 
2436 /*
2437  * process a list of expirable mountpoints with the intent of discarding any
2438  * mountpoints that aren't in use and haven't been touched since last we came
2439  * here
2440  */
2441 void mark_mounts_for_expiry(struct list_head *mounts)
2442 {
2443         struct mount *mnt, *next;
2444         LIST_HEAD(graveyard);
2445 
2446         if (list_empty(mounts))
2447                 return;
2448 
2449         namespace_lock();
2450         lock_mount_hash();
2451 
2452         /* extract from the expiration list every vfsmount that matches the
2453          * following criteria:
2454          * - only referenced by its parent vfsmount
2455          * - still marked for expiry (marked on the last call here; marks are
2456          *   cleared by mntput())
2457          */
2458         list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2459                 if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2460                         propagate_mount_busy(mnt, 1))
2461                         continue;
2462                 list_move(&mnt->mnt_expire, &graveyard);
2463         }
2464         while (!list_empty(&graveyard)) {
2465                 mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
2466                 touch_mnt_namespace(mnt->mnt_ns);
2467                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2468         }
2469         unlock_mount_hash();
2470         namespace_unlock();
2471 }
2472 
2473 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2474 
2475 /*
2476  * Ripoff of 'select_parent()'
2477  *
2478  * search the list of submounts for a given mountpoint, and move any
2479  * shrinkable submounts to the 'graveyard' list.
2480  */
2481 static int select_submounts(struct mount *parent, struct list_head *graveyard)
2482 {
2483         struct mount *this_parent = parent;
2484         struct list_head *next;
2485         int found = 0;
2486 
2487 repeat:
2488         next = this_parent->mnt_mounts.next;
2489 resume:
2490         while (next != &this_parent->mnt_mounts) {
2491                 struct list_head *tmp = next;
2492                 struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
2493 
2494                 next = tmp->next;
2495                 if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
2496                         continue;
2497                 /*
2498                  * Descend a level if the d_mounts list is non-empty.
2499                  */
2500                 if (!list_empty(&mnt->mnt_mounts)) {
2501                         this_parent = mnt;
2502                         goto repeat;
2503                 }
2504 
2505                 if (!propagate_mount_busy(mnt, 1)) {
2506                         list_move_tail(&mnt->mnt_expire, graveyard);
2507                         found++;
2508                 }
2509         }
2510         /*
2511          * All done at this level ... ascend and resume the search
2512          */
2513         if (this_parent != parent) {
2514                 next = this_parent->mnt_child.next;
2515                 this_parent = this_parent->mnt_parent;
2516                 goto resume;
2517         }
2518         return found;
2519 }
2520 
2521 /*
2522  * process a list of expirable mountpoints with the intent of discarding any
2523  * submounts of a specific parent mountpoint
2524  *
2525  * mount_lock must be held for write
2526  */
2527 static void shrink_submounts(struct mount *mnt)
2528 {
2529         LIST_HEAD(graveyard);
2530         struct mount *m;
2531 
2532         /* extract submounts of 'mountpoint' from the expiration list */
2533         while (select_submounts(mnt, &graveyard)) {
2534                 while (!list_empty(&graveyard)) {
2535                         m = list_first_entry(&graveyard, struct mount,
2536                                                 mnt_expire);
2537                         touch_mnt_namespace(m->mnt_ns);
2538                         umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2539                 }
2540         }
2541 }
2542 
2543 /*
2544  * Some copy_from_user() implementations do not return the exact number of
2545  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2546  * Note that this function differs from copy_from_user() in that it will oops
2547  * on bad values of `to', rather than returning a short copy.
2548  */
2549 static long exact_copy_from_user(void *to, const void __user * from,
2550                                  unsigned long n)
2551 {
2552         char *t = to;
2553         const char __user *f = from;
2554         char c;
2555 
2556         if (!access_ok(VERIFY_READ, from, n))
2557                 return n;
2558 
2559         while (n) {
2560                 if (__get_user(c, f)) {
2561                         memset(t, 0, n);
2562                         break;
2563                 }
2564                 *t++ = c;
2565                 f++;
2566                 n--;
2567         }
2568         return n;
2569 }
2570 
2571 int copy_mount_options(const void __user * data, unsigned long *where)
2572 {
2573         int i;
2574         unsigned long page;
2575         unsigned long size;
2576 
2577         *where = 0;
2578         if (!data)
2579                 return 0;
2580 
2581         if (!(page = __get_free_page(GFP_KERNEL)))
2582                 return -ENOMEM;
2583 
2584         /* We only care that *some* data at the address the user
2585          * gave us is valid.  Just in case, we'll zero
2586          * the remainder of the page.
2587          */
2588         /* copy_from_user cannot cross TASK_SIZE ! */
2589         size = TASK_SIZE - (unsigned long)data;
2590         if (size > PAGE_SIZE)
2591                 size = PAGE_SIZE;
2592 
2593         i = size - exact_copy_from_user((void *)page, data, size);
2594         if (!i) {
2595                 free_page(page);
2596                 return -EFAULT;
2597         }
2598         if (i != PAGE_SIZE)
2599                 memset((char *)page + i, 0, PAGE_SIZE - i);
2600         *where = page;
2601         return 0;
2602 }
2603 
2604 char *copy_mount_string(const void __user *data)
2605 {
2606         return data ? strndup_user(data, PAGE_SIZE) : NULL;
2607 }
2608 
2609 /*
2610  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2611  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2612  *
2613  * data is a (void *) that can point to any structure up to
2614  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2615  * information (or be NULL).
2616  *
2617  * Pre-0.97 versions of mount() didn't have a flags word.
2618  * When the flags word was introduced its top half was required
2619  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2620  * Therefore, if this magic number is present, it carries no information
2621  * and must be discarded.
2622  */
2623 long do_mount(const char *dev_name, const char __user *dir_name,
2624                 const char *type_page, unsigned long flags, void *data_page)
2625 {
2626         struct path path;
2627         int retval = 0;
2628         int mnt_flags = 0;
2629 
2630         /* Discard magic */
2631         if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2632                 flags &= ~MS_MGC_MSK;
2633 
2634         /* Basic sanity checks */
2635         if (data_page)
2636                 ((char *)data_page)[PAGE_SIZE - 1] = 0;
2637 
2638         /* ... and get the mountpoint */
2639         retval = user_path(dir_name, &path);
2640         if (retval)
2641                 return retval;
2642 
2643         retval = security_sb_mount(dev_name, &path,
2644                                    type_page, flags, data_page);
2645         if (!retval && !may_mount())
2646                 retval = -EPERM;
2647         if (retval)
2648                 goto dput_out;
2649 
2650         /* Default to relatime unless overriden */
2651         if (!(flags & MS_NOATIME))
2652                 mnt_flags |= MNT_RELATIME;
2653 
2654         /* Separate the per-mountpoint flags */
2655         if (flags & MS_NOSUID)
2656                 mnt_flags |= MNT_NOSUID;
2657         if (flags & MS_NODEV)
2658                 mnt_flags |= MNT_NODEV;
2659         if (flags & MS_NOEXEC)
2660                 mnt_flags |= MNT_NOEXEC;
2661         if (flags & MS_NOATIME)
2662                 mnt_flags |= MNT_NOATIME;
2663         if (flags & MS_NODIRATIME)
2664                 mnt_flags |= MNT_NODIRATIME;
2665         if (flags & MS_STRICTATIME)
2666                 mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2667         if (flags & MS_RDONLY)
2668                 mnt_flags |= MNT_READONLY;
2669 
2670         /* The default atime for remount is preservation */
2671         if ((flags & MS_REMOUNT) &&
2672             ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
2673                        MS_STRICTATIME)) == 0)) {
2674                 mnt_flags &= ~MNT_ATIME_MASK;
2675                 mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK;
2676         }
2677 
2678         flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2679                    MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2680                    MS_STRICTATIME);
2681 
2682         if (flags & MS_REMOUNT)
2683                 retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2684                                     data_page);
2685         else if (flags & MS_BIND)
2686                 retval = do_loopback(&path, dev_name, flags & MS_REC);
2687         else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2688                 retval = do_change_type(&path, flags);
2689         else if (flags & MS_MOVE)
2690                 retval = do_move_mount(&path, dev_name);
2691         else
2692                 retval = do_new_mount(&path, type_page, flags, mnt_flags,
2693                                       dev_name, data_page);
2694 dput_out:
2695         path_put(&path);
2696         return retval;
2697 }
2698 
2699 static void free_mnt_ns(struct mnt_namespace *ns)
2700 {
2701         ns_free_inum(&ns->ns);
2702         put_user_ns(ns->user_ns);
2703         kfree(ns);
2704 }
2705 
2706 /*
2707  * Assign a sequence number so we can detect when we attempt to bind
2708  * mount a reference to an older mount namespace into the current
2709  * mount namespace, preventing reference counting loops.  A 64bit
2710  * number incrementing at 10Ghz will take 12,427 years to wrap which
2711  * is effectively never, so we can ignore the possibility.
2712  */
2713 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
2714 
2715 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
2716 {
2717         struct mnt_namespace *new_ns;
2718         int ret;
2719 
2720         new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2721         if (!new_ns)
2722                 return ERR_PTR(-ENOMEM);
2723         ret = ns_alloc_inum(&new_ns->ns);
2724         if (ret) {
2725                 kfree(new_ns);
2726                 return ERR_PTR(ret);
2727         }
2728         new_ns->ns.ops = &mntns_operations;
2729         new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
2730         atomic_set(&new_ns->count, 1);
2731         new_ns->root = NULL;
2732         INIT_LIST_HEAD(&new_ns->list);
2733         init_waitqueue_head(&new_ns->poll);
2734         new_ns->event = 0;
2735         new_ns->user_ns = get_user_ns(user_ns);
2736         return new_ns;
2737 }
2738 
2739 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2740                 struct user_namespace *user_ns, struct fs_struct *new_fs)
2741 {
2742         struct mnt_namespace *new_ns;
2743         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2744         struct mount *p, *q;
2745         struct mount *old;
2746         struct mount *new;
2747         int copy_flags;
2748 
2749         BUG_ON(!ns);
2750 
2751         if (likely(!(flags & CLONE_NEWNS))) {
2752                 get_mnt_ns(ns);
2753                 return ns;
2754         }
2755 
2756         old = ns->root;
2757 
2758         new_ns = alloc_mnt_ns(user_ns);
2759         if (IS_ERR(new_ns))
2760                 return new_ns;
2761 
2762         namespace_lock();
2763         /* First pass: copy the tree topology */
2764         copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
2765         if (user_ns != ns->user_ns)
2766                 copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
2767         new = copy_tree(old, old->mnt.mnt_root, copy_flags);
2768         if (IS_ERR(new)) {
2769                 namespace_unlock();
2770                 free_mnt_ns(new_ns);
2771                 return ERR_CAST(new);
2772         }
2773         new_ns->root = new;
2774         list_add_tail(&new_ns->list, &new->mnt_list);
2775 
2776         /*
2777          * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2778          * as belonging to new namespace.  We have already acquired a private
2779          * fs_struct, so tsk->fs->lock is not needed.
2780          */
2781         p = old;
2782         q = new;
2783         while (p) {
2784                 q->mnt_ns = new_ns;
2785                 if (new_fs) {
2786                         if (&p->mnt == new_fs->root.mnt) {
2787                                 new_fs->root.mnt = mntget(&q->mnt);
2788                                 rootmnt = &p->mnt;
2789                         }
2790                         if (&p->mnt == new_fs->pwd.mnt) {
2791                                 new_fs->pwd.mnt = mntget(&q->mnt);
2792                                 pwdmnt = &p->mnt;
2793                         }
2794                 }
2795                 p = next_mnt(p, old);
2796                 q = next_mnt(q, new);
2797                 if (!q)
2798                         break;
2799                 while (p->mnt.mnt_root != q->mnt.mnt_root)
2800                         p = next_mnt(p, old);
2801         }
2802         namespace_unlock();
2803 
2804         if (rootmnt)
2805                 mntput(rootmnt);
2806         if (pwdmnt)
2807                 mntput(pwdmnt);
2808 
2809         return new_ns;
2810 }
2811 
2812 /**
2813  * create_mnt_ns - creates a private namespace and adds a root filesystem
2814  * @mnt: pointer to the new root filesystem mountpoint
2815  */
2816 static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
2817 {
2818         struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
2819         if (!IS_ERR(new_ns)) {
2820                 struct mount *mnt = real_mount(m);
2821                 mnt->mnt_ns = new_ns;
2822                 new_ns->root = mnt;
2823                 list_add(&mnt->mnt_list, &new_ns->list);
2824         } else {
2825                 mntput(m);
2826         }
2827         return new_ns;
2828 }
2829 
2830 struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
2831 {
2832         struct mnt_namespace *ns;
2833         struct super_block *s;
2834         struct path path;
2835         int err;
2836 
2837         ns = create_mnt_ns(mnt);
2838         if (IS_ERR(ns))
2839                 return ERR_CAST(ns);
2840 
2841         err = vfs_path_lookup(mnt->mnt_root, mnt,
2842                         name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
2843 
2844         put_mnt_ns(ns);
2845 
2846         if (err)
2847                 return ERR_PTR(err);
2848 
2849         /* trade a vfsmount reference for active sb one */
2850         s = path.mnt->mnt_sb;
2851         atomic_inc(&s->s_active);
2852         mntput(path.mnt);
2853         /* lock the sucker */
2854         down_write(&s->s_umount);
2855         /* ... and return the root of (sub)tree on it */
2856         return path.dentry;
2857 }
2858 EXPORT_SYMBOL(mount_subtree);
2859 
2860 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
2861                 char __user *, type, unsigned long, flags, void __user *, data)
2862 {
2863         int ret;
2864         char *kernel_type;
2865         char *kernel_dev;
2866         unsigned long data_page;
2867 
2868         kernel_type = copy_mount_string(type);
2869         ret = PTR_ERR(kernel_type);
2870         if (IS_ERR(kernel_type))
2871                 goto out_type;
2872 
2873         kernel_dev = copy_mount_string(dev_name);
2874         ret = PTR_ERR(kernel_dev);
2875         if (IS_ERR(kernel_dev))
2876                 goto out_dev;
2877 
2878         ret = copy_mount_options(data, &data_page);
2879         if (ret < 0)
2880                 goto out_data;
2881 
2882         ret = do_mount(kernel_dev, dir_name, kernel_type, flags,
2883                 (void *) data_page);
2884 
2885         free_page(data_page);
2886 out_data:
2887         kfree(kernel_dev);
2888 out_dev:
2889         kfree(kernel_type);
2890 out_type:
2891         return ret;
2892 }
2893 
2894 /*
2895  * Return true if path is reachable from root
2896  *
2897  * namespace_sem or mount_lock is held
2898  */
2899 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
2900                          const struct path *root)
2901 {
2902         while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
2903                 dentry = mnt->mnt_mountpoint;
2904                 mnt = mnt->mnt_parent;
2905         }
2906         return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
2907 }
2908 
2909 int path_is_under(struct path *path1, struct path *path2)
2910 {
2911         int res;
2912         read_seqlock_excl(&mount_lock);
2913         res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
2914         read_sequnlock_excl(&mount_lock);
2915         return res;
2916 }
2917 EXPORT_SYMBOL(path_is_under);
2918 
2919 /*
2920  * pivot_root Semantics:
2921  * Moves the root file system of the current process to the directory put_old,
2922  * makes new_root as the new root file system of the current process, and sets
2923  * root/cwd of all processes which had them on the current root to new_root.
2924  *
2925  * Restrictions:
2926  * The new_root and put_old must be directories, and  must not be on the
2927  * same file  system as the current process root. The put_old  must  be
2928  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
2929  * pointed to by put_old must yield the same directory as new_root. No other
2930  * file system may be mounted on put_old. After all, new_root is a mountpoint.
2931  *
2932  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
2933  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
2934  * in this situation.
2935  *
2936  * Notes:
2937  *  - we don't move root/cwd if they are not at the root (reason: if something
2938  *    cared enough to change them, it's probably wrong to force them elsewhere)
2939  *  - it's okay to pick a root that isn't the root of a file system, e.g.
2940  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
2941  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
2942  *    first.
2943  */
2944 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
2945                 const char __user *, put_old)
2946 {
2947         struct path new, old, parent_path, root_parent, root;
2948         struct mount *new_mnt, *root_mnt, *old_mnt;
2949         struct mountpoint *old_mp, *root_mp;
2950         int error;
2951 
2952         if (!may_mount())
2953                 return -EPERM;
2954 
2955         error = user_path_dir(new_root, &new);
2956         if (error)
2957                 goto out0;
2958 
2959         error = user_path_dir(put_old, &old);
2960         if (error)
2961                 goto out1;
2962 
2963         error = security_sb_pivotroot(&old, &new);
2964         if (error)
2965                 goto out2;
2966 
2967         get_fs_root(current->fs, &root);
2968         old_mp = lock_mount(&old);
2969         error = PTR_ERR(old_mp);
2970         if (IS_ERR(old_mp))
2971                 goto out3;
2972 
2973         error = -EINVAL;
2974         new_mnt = real_mount(new.mnt);
2975         root_mnt = real_mount(root.mnt);
2976         old_mnt = real_mount(old.mnt);
2977         if (IS_MNT_SHARED(old_mnt) ||
2978                 IS_MNT_SHARED(new_mnt->mnt_parent) ||
2979                 IS_MNT_SHARED(root_mnt->mnt_parent))
2980                 goto out4;
2981         if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
2982                 goto out4;
2983         if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
2984                 goto out4;
2985         error = -ENOENT;
2986         if (d_unlinked(new.dentry))
2987                 goto out4;
2988         error = -EBUSY;
2989         if (new_mnt == root_mnt || old_mnt == root_mnt)
2990                 goto out4; /* loop, on the same file system  */
2991         error = -EINVAL;
2992         if (root.mnt->mnt_root != root.dentry)
2993                 goto out4; /* not a mountpoint */
2994         if (!mnt_has_parent(root_mnt))
2995                 goto out4; /* not attached */
2996         root_mp = root_mnt->mnt_mp;
2997         if (new.mnt->mnt_root != new.dentry)
2998                 goto out4; /* not a mountpoint */
2999         if (!mnt_has_parent(new_mnt))
3000                 goto out4; /* not attached */
3001         /* make sure we can reach put_old from new_root */
3002         if (!is_path_reachable(old_mnt, old.dentry, &new))
3003                 goto out4;
3004         /* make certain new is below the root */
3005         if (!is_path_reachable(new_mnt, new.dentry, &root))
3006                 goto out4;
3007         root_mp->m_count++; /* pin it so it won't go away */
3008         lock_mount_hash();
3009         detach_mnt(new_mnt, &parent_path);
3010         detach_mnt(root_mnt, &root_parent);
3011         if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
3012                 new_mnt->mnt.mnt_flags |= MNT_LOCKED;
3013                 root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
3014         }
3015         /* mount old root on put_old */
3016         attach_mnt(root_mnt, old_mnt, old_mp);
3017         /* mount new_root on / */
3018         attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
3019         touch_mnt_namespace(current->nsproxy->mnt_ns);
3020         /* A moved mount should not expire automatically */
3021         list_del_init(&new_mnt->mnt_expire);
3022         unlock_mount_hash();
3023         chroot_fs_refs(&root, &new);
3024         put_mountpoint(root_mp);
3025         error = 0;
3026 out4:
3027         unlock_mount(old_mp);
3028         if (!error) {
3029                 path_put(&root_parent);
3030                 path_put(&parent_path);
3031         }
3032 out3:
3033         path_put(&root);
3034 out2:
3035         path_put(&old);
3036 out1:
3037         path_put(&new);
3038 out0:
3039         return error;
3040 }
3041 
3042 static void __init init_mount_tree(void)
3043 {
3044         struct vfsmount *mnt;
3045         struct mnt_namespace *ns;
3046         struct path root;
3047         struct file_system_type *type;
3048 
3049         type = get_fs_type("rootfs");
3050         if (!type)
3051                 panic("Can't find rootfs type");
3052         mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
3053         put_filesystem(type);
3054         if (IS_ERR(mnt))
3055                 panic("Can't create rootfs");
3056 
3057         ns = create_mnt_ns(mnt);
3058         if (IS_ERR(ns))
3059                 panic("Can't allocate initial namespace");
3060 
3061         init_task.nsproxy->mnt_ns = ns;
3062         get_mnt_ns(ns);
3063 
3064         root.mnt = mnt;
3065         root.dentry = mnt->mnt_root;
3066         mnt->mnt_flags |= MNT_LOCKED;
3067 
3068         set_fs_pwd(current->fs, &root);
3069         set_fs_root(current->fs, &root);
3070 }
3071 
3072 void __init mnt_init(void)
3073 {
3074         unsigned u;
3075         int err;
3076 
3077         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
3078                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
3079 
3080         mount_hashtable = alloc_large_system_hash("Mount-cache",
3081                                 sizeof(struct hlist_head),
3082                                 mhash_entries, 19,
3083                                 0,
3084                                 &m_hash_shift, &m_hash_mask, 0, 0);
3085         mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
3086                                 sizeof(struct hlist_head),
3087                                 mphash_entries, 19,
3088                                 0,
3089                                 &mp_hash_shift, &mp_hash_mask, 0, 0);
3090 
3091         if (!mount_hashtable || !mountpoint_hashtable)
3092                 panic("Failed to allocate mount hash table\n");
3093 
3094         for (u = 0; u <= m_hash_mask; u++)
3095                 INIT_HLIST_HEAD(&mount_hashtable[u]);
3096         for (u = 0; u <= mp_hash_mask; u++)
3097                 INIT_HLIST_HEAD(&mountpoint_hashtable[u]);
3098 
3099         kernfs_init();
3100 
3101         err = sysfs_init();
3102         if (err)
3103                 printk(KERN_WARNING "%s: sysfs_init error: %d\n",
3104                         __func__, err);
3105         fs_kobj = kobject_create_and_add("fs", NULL);
3106         if (!fs_kobj)
3107                 printk(KERN_WARNING "%s: kobj create error\n", __func__);
3108         init_rootfs();
3109         init_mount_tree();
3110 }
3111 
3112 void put_mnt_ns(struct mnt_namespace *ns)
3113 {
3114         if (!atomic_dec_and_test(&ns->count))
3115                 return;
3116         drop_collected_mounts(&ns->root->mnt);
3117         free_mnt_ns(ns);
3118 }
3119 
3120 struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
3121 {
3122         struct vfsmount *mnt;
3123         mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
3124         if (!IS_ERR(mnt)) {
3125                 /*
3126                  * it is a longterm mount, don't release mnt until
3127                  * we unmount before file sys is unregistered
3128                 */
3129                 real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
3130         }
3131         return mnt;
3132 }
3133 EXPORT_SYMBOL_GPL(kern_mount_data);
3134 
3135 void kern_unmount(struct vfsmount *mnt)
3136 {
3137         /* release long term mount so mount point can be released */
3138         if (!IS_ERR_OR_NULL(mnt)) {
3139                 real_mount(mnt)->mnt_ns = NULL;
3140                 synchronize_rcu();      /* yecchhh... */
3141                 mntput(mnt);
3142         }
3143 }
3144 EXPORT_SYMBOL(kern_unmount);
3145 
3146 bool our_mnt(struct vfsmount *mnt)
3147 {
3148         return check_mnt(real_mount(mnt));
3149 }
3150 
3151 bool current_chrooted(void)
3152 {
3153         /* Does the current process have a non-standard root */
3154         struct path ns_root;
3155         struct path fs_root;
3156         bool chrooted;
3157 
3158         /* Find the namespace root */
3159         ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
3160         ns_root.dentry = ns_root.mnt->mnt_root;
3161         path_get(&ns_root);
3162         while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
3163                 ;
3164 
3165         get_fs_root(current->fs, &fs_root);
3166 
3167         chrooted = !path_equal(&fs_root, &ns_root);
3168 
3169         path_put(&fs_root);
3170         path_put(&ns_root);
3171 
3172         return chrooted;
3173 }
3174 
3175 static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
3176 {
3177         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
3178         int new_flags = *new_mnt_flags;
3179         struct mount *mnt;
3180         bool visible = false;
3181 
3182         if (unlikely(!ns))
3183                 return false;
3184 
3185         down_read(&namespace_sem);
3186         list_for_each_entry(mnt, &ns->list, mnt_list) {
3187                 struct mount *child;
3188                 if (mnt->mnt.mnt_sb->s_type != type)
3189                         continue;
3190 
3191                 /* This mount is not fully visible if it's root directory
3192                  * is not the root directory of the filesystem.
3193                  */
3194                 if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
3195                         continue;
3196 
3197                 /* Verify the mount flags are equal to or more permissive
3198                  * than the proposed new mount.
3199                  */
3200                 if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
3201                     !(new_flags & MNT_READONLY))
3202                         continue;
3203                 if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
3204                     !(new_flags & MNT_NODEV))
3205                         continue;
3206                 if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
3207                     ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
3208                         continue;
3209 
3210                 /* This mount is not fully visible if there are any
3211                  * locked child mounts that cover anything except for
3212                  * empty directories.
3213                  */
3214                 list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
3215                         struct inode *inode = child->mnt_mountpoint->d_inode;
3216                         /* Only worry about locked mounts */
3217                         if (!(mnt->mnt.mnt_flags & MNT_LOCKED))
3218                                 continue;
3219                         /* Is the directory permanetly empty? */
3220                         if (!is_empty_dir_inode(inode))
3221                                 goto next;
3222                 }
3223                 /* Preserve the locked attributes */
3224                 *new_mnt_flags |= mnt->mnt.mnt_flags & (MNT_LOCK_READONLY | \
3225                                                         MNT_LOCK_NODEV    | \
3226                                                         MNT_LOCK_ATIME);
3227                 visible = true;
3228                 goto found;
3229         next:   ;
3230         }
3231 found:
3232         up_read(&namespace_sem);
3233         return visible;
3234 }
3235 
3236 static struct ns_common *mntns_get(struct task_struct *task)
3237 {
3238         struct ns_common *ns = NULL;
3239         struct nsproxy *nsproxy;
3240 
3241         task_lock(task);
3242         nsproxy = task->nsproxy;
3243         if (nsproxy) {
3244                 ns = &nsproxy->mnt_ns->ns;
3245                 get_mnt_ns(to_mnt_ns(ns));
3246         }
3247         task_unlock(task);
3248 
3249         return ns;
3250 }
3251 
3252 static void mntns_put(struct ns_common *ns)
3253 {
3254         put_mnt_ns(to_mnt_ns(ns));
3255 }
3256 
3257 static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
3258 {
3259         struct fs_struct *fs = current->fs;
3260         struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
3261         struct path root;
3262 
3263         if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
3264             !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
3265             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
3266                 return -EPERM;
3267 
3268         if (fs->users != 1)
3269                 return -EINVAL;
3270 
3271         get_mnt_ns(mnt_ns);
3272         put_mnt_ns(nsproxy->mnt_ns);
3273         nsproxy->mnt_ns = mnt_ns;
3274 
3275         /* Find the root */
3276         root.mnt    = &mnt_ns->root->mnt;
3277         root.dentry = mnt_ns->root->mnt.mnt_root;
3278         path_get(&root);
3279         while(d_mountpoint(root.dentry) && follow_down_one(&root))
3280                 ;
3281 
3282         /* Update the pwd and root */
3283         set_fs_pwd(fs, &root);
3284         set_fs_root(fs, &root);
3285 
3286         path_put(&root);
3287         return 0;
3288 }
3289 
3290 const struct proc_ns_operations mntns_operations = {
3291         .name           = "mnt",
3292         .type           = CLONE_NEWNS,
3293         .get            = mntns_get,
3294         .put            = mntns_put,
3295         .install        = mntns_install,
3296 };
3297 

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