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