1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  linux/fs/pnode.c
4 *
5 * (C) Copyright IBM Corporation 2005.
6 *	Author : Ram Pai (linuxram@us.ibm.com)
7 */
8#include <linux/mnt_namespace.h>
9#include <linux/mount.h>
10#include <linux/fs.h>
11#include <linux/nsproxy.h>
12#include <uapi/linux/mount.h>
13#include "internal.h"
14#include "pnode.h"
15
16/* return the next shared peer mount of @p */
17static inline struct mount *next_peer(struct mount *p)
18{
19	return list_entry(p->mnt_share.next, struct mount, mnt_share);
20}
21
22static inline struct mount *first_slave(struct mount *p)
23{
24	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
25}
26
27static inline struct mount *last_slave(struct mount *p)
28{
29	return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
30}
31
32static inline struct mount *next_slave(struct mount *p)
33{
34	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
35}
36
37static struct mount *get_peer_under_root(struct mount *mnt,
38					 struct mnt_namespace *ns,
39					 const struct path *root)
40{
41	struct mount *m = mnt;
42
43	do {
44		/* Check the namespace first for optimization */
45		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
46			return m;
47
48		m = next_peer(m);
49	} while (m != mnt);
50
51	return NULL;
52}
53
54/*
55 * Get ID of closest dominating peer group having a representative
56 * under the given root.
57 *
58 * Caller must hold namespace_sem
59 */
60int get_dominating_id(struct mount *mnt, const struct path *root)
61{
62	struct mount *m;
63
64	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
65		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
66		if (d)
67			return d->mnt_group_id;
68	}
69
70	return 0;
71}
72
73static int do_make_slave(struct mount *mnt)
74{
75	struct mount *master, *slave_mnt;
76
77	if (list_empty(&mnt->mnt_share)) {
78		if (IS_MNT_SHARED(mnt)) {
79			mnt_release_group_id(mnt);
80			CLEAR_MNT_SHARED(mnt);
81		}
82		master = mnt->mnt_master;
83		if (!master) {
84			struct list_head *p = &mnt->mnt_slave_list;
85			while (!list_empty(p)) {
86				slave_mnt = list_first_entry(p,
87						struct mount, mnt_slave);
88				list_del_init(&slave_mnt->mnt_slave);
89				slave_mnt->mnt_master = NULL;
90			}
91			return 0;
92		}
93	} else {
94		struct mount *m;
95		/*
96		 * slave 'mnt' to a peer mount that has the
97		 * same root dentry. If none is available then
98		 * slave it to anything that is available.
99		 */
100		for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
101			if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
102				master = m;
103				break;
104			}
105		}
106		list_del_init(&mnt->mnt_share);
107		mnt->mnt_group_id = 0;
108		CLEAR_MNT_SHARED(mnt);
109	}
110	list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
111		slave_mnt->mnt_master = master;
112	list_move(&mnt->mnt_slave, &master->mnt_slave_list);
113	list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
114	INIT_LIST_HEAD(&mnt->mnt_slave_list);
115	mnt->mnt_master = master;
116	return 0;
117}
118
119/*
120 * vfsmount lock must be held for write
121 */
122void change_mnt_propagation(struct mount *mnt, int type)
123{
124	if (type == MS_SHARED) {
125		set_mnt_shared(mnt);
126		return;
127	}
128	do_make_slave(mnt);
129	if (type != MS_SLAVE) {
130		list_del_init(&mnt->mnt_slave);
131		mnt->mnt_master = NULL;
132		if (type == MS_UNBINDABLE)
133			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
134		else
135			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
136	}
137}
138
139/*
140 * get the next mount in the propagation tree.
141 * @m: the mount seen last
142 * @origin: the original mount from where the tree walk initiated
143 *
144 * Note that peer groups form contiguous segments of slave lists.
145 * We rely on that in get_source() to be able to find out if
146 * vfsmount found while iterating with propagation_next() is
147 * a peer of one we'd found earlier.
148 */
149static struct mount *propagation_next(struct mount *m,
150					 struct mount *origin)
151{
152	/* are there any slaves of this mount? */
153	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
154		return first_slave(m);
155
156	while (1) {
157		struct mount *master = m->mnt_master;
158
159		if (master == origin->mnt_master) {
160			struct mount *next = next_peer(m);
161			return (next == origin) ? NULL : next;
162		} else if (m->mnt_slave.next != &master->mnt_slave_list)
163			return next_slave(m);
164
165		/* back at master */
166		m = master;
167	}
168}
169
170static struct mount *skip_propagation_subtree(struct mount *m,
171						struct mount *origin)
172{
173	/*
174	 * Advance m such that propagation_next will not return
175	 * the slaves of m.
176	 */
177	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
178		m = last_slave(m);
179
180	return m;
181}
182
183static struct mount *next_group(struct mount *m, struct mount *origin)
184{
185	while (1) {
186		while (1) {
187			struct mount *next;
188			if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
189				return first_slave(m);
190			next = next_peer(m);
191			if (m->mnt_group_id == origin->mnt_group_id) {
192				if (next == origin)
193					return NULL;
194			} else if (m->mnt_slave.next != &next->mnt_slave)
195				break;
196			m = next;
197		}
198		/* m is the last peer */
199		while (1) {
200			struct mount *master = m->mnt_master;
201			if (m->mnt_slave.next != &master->mnt_slave_list)
202				return next_slave(m);
203			m = next_peer(master);
204			if (master->mnt_group_id == origin->mnt_group_id)
205				break;
206			if (master->mnt_slave.next == &m->mnt_slave)
207				break;
208			m = master;
209		}
210		if (m == origin)
211			return NULL;
212	}
213}
214
215/* all accesses are serialized by namespace_sem */
216static struct mount *last_dest, *first_source, *last_source, *dest_master;
217static struct hlist_head *list;
218
219static inline bool peers(const struct mount *m1, const struct mount *m2)
220{
221	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
222}
223
224static int propagate_one(struct mount *m, struct mountpoint *dest_mp)
225{
226	struct mount *child;
227	int type;
228	/* skip ones added by this propagate_mnt() */
229	if (IS_MNT_NEW(m))
230		return 0;
231	/* skip if mountpoint isn't covered by it */
232	if (!is_subdir(dest_mp->m_dentry, m->mnt.mnt_root))
233		return 0;
234	if (peers(m, last_dest)) {
235		type = CL_MAKE_SHARED;
236	} else {
237		struct mount *n, *p;
238		bool done;
239		for (n = m; ; n = p) {
240			p = n->mnt_master;
241			if (p == dest_master || IS_MNT_MARKED(p))
242				break;
243		}
244		do {
245			struct mount *parent = last_source->mnt_parent;
246			if (peers(last_source, first_source))
247				break;
248			done = parent->mnt_master == p;
249			if (done && peers(n, parent))
250				break;
251			last_source = last_source->mnt_master;
252		} while (!done);
253
254		type = CL_SLAVE;
255		/* beginning of peer group among the slaves? */
256		if (IS_MNT_SHARED(m))
257			type |= CL_MAKE_SHARED;
258	}
259
260	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
261	if (IS_ERR(child))
262		return PTR_ERR(child);
263	read_seqlock_excl(&mount_lock);
264	mnt_set_mountpoint(m, dest_mp, child);
265	if (m->mnt_master != dest_master)
266		SET_MNT_MARK(m->mnt_master);
267	read_sequnlock_excl(&mount_lock);
268	last_dest = m;
269	last_source = child;
270	hlist_add_head(&child->mnt_hash, list);
271	return count_mounts(m->mnt_ns, child);
272}
273
274/*
275 * mount 'source_mnt' under the destination 'dest_mnt' at
276 * dentry 'dest_dentry'. And propagate that mount to
277 * all the peer and slave mounts of 'dest_mnt'.
278 * Link all the new mounts into a propagation tree headed at
279 * source_mnt. Also link all the new mounts using ->mnt_list
280 * headed at source_mnt's ->mnt_list
281 *
282 * @dest_mnt: destination mount.
283 * @dest_dentry: destination dentry.
284 * @source_mnt: source mount.
285 * @tree_list : list of heads of trees to be attached.
286 */
287int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
288		    struct mount *source_mnt, struct hlist_head *tree_list)
289{
290	struct mount *m, *n;
291	int ret = 0;
292
293	/*
294	 * we don't want to bother passing tons of arguments to
295	 * propagate_one(); everything is serialized by namespace_sem,
296	 * so globals will do just fine.
297	 */
298	last_dest = dest_mnt;
299	first_source = source_mnt;
300	last_source = source_mnt;
301	list = tree_list;
302	dest_master = dest_mnt->mnt_master;
303
304	/* all peers of dest_mnt, except dest_mnt itself */
305	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
306		ret = propagate_one(n, dest_mp);
307		if (ret)
308			goto out;
309	}
310
311	/* all slave groups */
312	for (m = next_group(dest_mnt, dest_mnt); m;
313			m = next_group(m, dest_mnt)) {
314		/* everything in that slave group */
315		n = m;
316		do {
317			ret = propagate_one(n, dest_mp);
318			if (ret)
319				goto out;
320			n = next_peer(n);
321		} while (n != m);
322	}
323out:
324	read_seqlock_excl(&mount_lock);
325	hlist_for_each_entry(n, tree_list, mnt_hash) {
326		m = n->mnt_parent;
327		if (m->mnt_master != dest_mnt->mnt_master)
328			CLEAR_MNT_MARK(m->mnt_master);
329	}
330	read_sequnlock_excl(&mount_lock);
331	return ret;
332}
333
334static struct mount *find_topper(struct mount *mnt)
335{
336	/* If there is exactly one mount covering mnt completely return it. */
337	struct mount *child;
338
339	if (!list_is_singular(&mnt->mnt_mounts))
340		return NULL;
341
342	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
343	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
344		return NULL;
345
346	return child;
347}
348
349/*
350 * return true if the refcount is greater than count
351 */
352static inline int do_refcount_check(struct mount *mnt, int count)
353{
354	return mnt_get_count(mnt) > count;
355}
356
357/**
358 * propagation_would_overmount - check whether propagation from @from
359 *                               would overmount @to
360 * @from: shared mount
361 * @to:   mount to check
362 * @mp:   future mountpoint of @to on @from
363 *
364 * If @from propagates mounts to @to, @from and @to must either be peers
365 * or one of the masters in the hierarchy of masters of @to must be a
366 * peer of @from.
367 *
368 * If the root of the @to mount is equal to the future mountpoint @mp of
369 * the @to mount on @from then @to will be overmounted by whatever is
370 * propagated to it.
371 *
372 * Context: This function expects namespace_lock() to be held and that
373 *          @mp is stable.
374 * Return: If @from overmounts @to, true is returned, false if not.
375 */
376bool propagation_would_overmount(const struct mount *from,
377				 const struct mount *to,
378				 const struct mountpoint *mp)
379{
380	if (!IS_MNT_SHARED(from))
381		return false;
382
383	if (IS_MNT_NEW(to))
384		return false;
385
386	if (to->mnt.mnt_root != mp->m_dentry)
387		return false;
388
389	for (const struct mount *m = to; m; m = m->mnt_master) {
390		if (peers(from, m))
391			return true;
392	}
393
394	return false;
395}
396
397/*
398 * check if the mount 'mnt' can be unmounted successfully.
399 * @mnt: the mount to be checked for unmount
400 * NOTE: unmounting 'mnt' would naturally propagate to all
401 * other mounts its parent propagates to.
402 * Check if any of these mounts that **do not have submounts**
403 * have more references than 'refcnt'. If so return busy.
404 *
405 * vfsmount lock must be held for write
406 */
407int propagate_mount_busy(struct mount *mnt, int refcnt)
408{
409	struct mount *m, *child, *topper;
410	struct mount *parent = mnt->mnt_parent;
411
412	if (mnt == parent)
413		return do_refcount_check(mnt, refcnt);
414
415	/*
416	 * quickly check if the current mount can be unmounted.
417	 * If not, we don't have to go checking for all other
418	 * mounts
419	 */
420	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
421		return 1;
422
423	for (m = propagation_next(parent, parent); m;
424	     		m = propagation_next(m, parent)) {
425		int count = 1;
426		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
427		if (!child)
428			continue;
429
430		/* Is there exactly one mount on the child that covers
431		 * it completely whose reference should be ignored?
432		 */
433		topper = find_topper(child);
434		if (topper)
435			count += 1;
436		else if (!list_empty(&child->mnt_mounts))
437			continue;
438
439		if (do_refcount_check(child, count))
440			return 1;
441	}
442	return 0;
443}
444
445/*
446 * Clear MNT_LOCKED when it can be shown to be safe.
447 *
448 * mount_lock lock must be held for write
449 */
450void propagate_mount_unlock(struct mount *mnt)
451{
452	struct mount *parent = mnt->mnt_parent;
453	struct mount *m, *child;
454
455	BUG_ON(parent == mnt);
456
457	for (m = propagation_next(parent, parent); m;
458			m = propagation_next(m, parent)) {
459		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
460		if (child)
461			child->mnt.mnt_flags &= ~MNT_LOCKED;
462	}
463}
464
465static void umount_one(struct mount *mnt, struct list_head *to_umount)
466{
467	CLEAR_MNT_MARK(mnt);
468	mnt->mnt.mnt_flags |= MNT_UMOUNT;
469	list_del_init(&mnt->mnt_child);
470	list_del_init(&mnt->mnt_umounting);
471	move_from_ns(mnt, to_umount);
472}
473
474/*
475 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
476 * parent propagates to.
477 */
478static bool __propagate_umount(struct mount *mnt,
479			       struct list_head *to_umount,
480			       struct list_head *to_restore)
481{
482	bool progress = false;
483	struct mount *child;
484
485	/*
486	 * The state of the parent won't change if this mount is
487	 * already unmounted or marked as without children.
488	 */
489	if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
490		goto out;
491
492	/* Verify topper is the only grandchild that has not been
493	 * speculatively unmounted.
494	 */
495	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
496		if (child->mnt_mountpoint == mnt->mnt.mnt_root)
497			continue;
498		if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
499			continue;
500		/* Found a mounted child */
501		goto children;
502	}
503
504	/* Mark mounts that can be unmounted if not locked */
505	SET_MNT_MARK(mnt);
506	progress = true;
507
508	/* If a mount is without children and not locked umount it. */
509	if (!IS_MNT_LOCKED(mnt)) {
510		umount_one(mnt, to_umount);
511	} else {
512children:
513		list_move_tail(&mnt->mnt_umounting, to_restore);
514	}
515out:
516	return progress;
517}
518
519static void umount_list(struct list_head *to_umount,
520			struct list_head *to_restore)
521{
522	struct mount *mnt, *child, *tmp;
523	list_for_each_entry(mnt, to_umount, mnt_list) {
524		list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
525			/* topper? */
526			if (child->mnt_mountpoint == mnt->mnt.mnt_root)
527				list_move_tail(&child->mnt_umounting, to_restore);
528			else
529				umount_one(child, to_umount);
530		}
531	}
532}
533
534static void restore_mounts(struct list_head *to_restore)
535{
536	/* Restore mounts to a clean working state */
537	while (!list_empty(to_restore)) {
538		struct mount *mnt, *parent;
539		struct mountpoint *mp;
540
541		mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
542		CLEAR_MNT_MARK(mnt);
543		list_del_init(&mnt->mnt_umounting);
544
545		/* Should this mount be reparented? */
546		mp = mnt->mnt_mp;
547		parent = mnt->mnt_parent;
548		while (parent->mnt.mnt_flags & MNT_UMOUNT) {
549			mp = parent->mnt_mp;
550			parent = parent->mnt_parent;
551		}
552		if (parent != mnt->mnt_parent)
553			mnt_change_mountpoint(parent, mp, mnt);
554	}
555}
556
557static void cleanup_umount_visitations(struct list_head *visited)
558{
559	while (!list_empty(visited)) {
560		struct mount *mnt =
561			list_first_entry(visited, struct mount, mnt_umounting);
562		list_del_init(&mnt->mnt_umounting);
563	}
564}
565
566/*
567 * collect all mounts that receive propagation from the mount in @list,
568 * and return these additional mounts in the same list.
569 * @list: the list of mounts to be unmounted.
570 *
571 * vfsmount lock must be held for write
572 */
573int propagate_umount(struct list_head *list)
574{
575	struct mount *mnt;
576	LIST_HEAD(to_restore);
577	LIST_HEAD(to_umount);
578	LIST_HEAD(visited);
579
580	/* Find candidates for unmounting */
581	list_for_each_entry_reverse(mnt, list, mnt_list) {
582		struct mount *parent = mnt->mnt_parent;
583		struct mount *m;
584
585		/*
586		 * If this mount has already been visited it is known that it's
587		 * entire peer group and all of their slaves in the propagation
588		 * tree for the mountpoint has already been visited and there is
589		 * no need to visit them again.
590		 */
591		if (!list_empty(&mnt->mnt_umounting))
592			continue;
593
594		list_add_tail(&mnt->mnt_umounting, &visited);
595		for (m = propagation_next(parent, parent); m;
596		     m = propagation_next(m, parent)) {
597			struct mount *child = __lookup_mnt(&m->mnt,
598							   mnt->mnt_mountpoint);
599			if (!child)
600				continue;
601
602			if (!list_empty(&child->mnt_umounting)) {
603				/*
604				 * If the child has already been visited it is
605				 * know that it's entire peer group and all of
606				 * their slaves in the propgation tree for the
607				 * mountpoint has already been visited and there
608				 * is no need to visit this subtree again.
609				 */
610				m = skip_propagation_subtree(m, parent);
611				continue;
612			} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
613				/*
614				 * We have come accross an partially unmounted
615				 * mount in list that has not been visited yet.
616				 * Remember it has been visited and continue
617				 * about our merry way.
618				 */
619				list_add_tail(&child->mnt_umounting, &visited);
620				continue;
621			}
622
623			/* Check the child and parents while progress is made */
624			while (__propagate_umount(child,
625						  &to_umount, &to_restore)) {
626				/* Is the parent a umount candidate? */
627				child = child->mnt_parent;
628				if (list_empty(&child->mnt_umounting))
629					break;
630			}
631		}
632	}
633
634	umount_list(&to_umount, &to_restore);
635	restore_mounts(&to_restore);
636	cleanup_umount_visitations(&visited);
637	list_splice_tail(&to_umount, list);
638
639	return 0;
640}
641