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  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 mountpoint *mp;
218static struct hlist_head *list;
219
220static inline bool peers(struct mount *m1, struct mount *m2)
221{
222	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
223}
224
225static int propagate_one(struct mount *m)
226{
227	struct mount *child;
228	int type;
229	/* skip ones added by this propagate_mnt() */
230	if (IS_MNT_NEW(m))
231		return 0;
232	/* skip if mountpoint isn't covered by it */
233	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
234		return 0;
235	if (peers(m, last_dest)) {
236		type = CL_MAKE_SHARED;
237	} else {
238		struct mount *n, *p;
239		bool done;
240		for (n = m; ; n = p) {
241			p = n->mnt_master;
242			if (p == dest_master || IS_MNT_MARKED(p))
243				break;
244		}
245		do {
246			struct mount *parent = last_source->mnt_parent;
247			if (last_source == first_source)
248				break;
249			done = parent->mnt_master == p;
250			if (done && peers(n, parent))
251				break;
252			last_source = last_source->mnt_master;
253		} while (!done);
254
255		type = CL_SLAVE;
256		/* beginning of peer group among the slaves? */
257		if (IS_MNT_SHARED(m))
258			type |= CL_MAKE_SHARED;
259	}
260		
261	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
262	if (IS_ERR(child))
263		return PTR_ERR(child);
264	read_seqlock_excl(&mount_lock);
265	mnt_set_mountpoint(m, mp, child);
266	if (m->mnt_master != dest_master)
267		SET_MNT_MARK(m->mnt_master);
268	read_sequnlock_excl(&mount_lock);
269	last_dest = m;
270	last_source = child;
271	hlist_add_head(&child->mnt_hash, list);
272	return count_mounts(m->mnt_ns, child);
273}
274
275/*
276 * mount 'source_mnt' under the destination 'dest_mnt' at
277 * dentry 'dest_dentry'. And propagate that mount to
278 * all the peer and slave mounts of 'dest_mnt'.
279 * Link all the new mounts into a propagation tree headed at
280 * source_mnt. Also link all the new mounts using ->mnt_list
281 * headed at source_mnt's ->mnt_list
282 *
283 * @dest_mnt: destination mount.
284 * @dest_dentry: destination dentry.
285 * @source_mnt: source mount.
286 * @tree_list : list of heads of trees to be attached.
287 */
288int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
289		    struct mount *source_mnt, struct hlist_head *tree_list)
290{
291	struct mount *m, *n;
292	int ret = 0;
293
294	/*
295	 * we don't want to bother passing tons of arguments to
296	 * propagate_one(); everything is serialized by namespace_sem,
297	 * so globals will do just fine.
298	 */
299	last_dest = dest_mnt;
300	first_source = source_mnt;
301	last_source = source_mnt;
302	mp = dest_mp;
303	list = tree_list;
304	dest_master = dest_mnt->mnt_master;
305
306	/* all peers of dest_mnt, except dest_mnt itself */
307	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
308		ret = propagate_one(n);
309		if (ret)
310			goto out;
311	}
312
313	/* all slave groups */
314	for (m = next_group(dest_mnt, dest_mnt); m;
315			m = next_group(m, dest_mnt)) {
316		/* everything in that slave group */
317		n = m;
318		do {
319			ret = propagate_one(n);
320			if (ret)
321				goto out;
322			n = next_peer(n);
323		} while (n != m);
324	}
325out:
326	read_seqlock_excl(&mount_lock);
327	hlist_for_each_entry(n, tree_list, mnt_hash) {
328		m = n->mnt_parent;
329		if (m->mnt_master != dest_mnt->mnt_master)
330			CLEAR_MNT_MARK(m->mnt_master);
331	}
332	read_sequnlock_excl(&mount_lock);
333	return ret;
334}
335
336static struct mount *find_topper(struct mount *mnt)
337{
338	/* If there is exactly one mount covering mnt completely return it. */
339	struct mount *child;
340
341	if (!list_is_singular(&mnt->mnt_mounts))
342		return NULL;
343
344	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
345	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
346		return NULL;
347
348	return child;
349}
350
351/*
352 * return true if the refcount is greater than count
353 */
354static inline int do_refcount_check(struct mount *mnt, int count)
355{
356	return mnt_get_count(mnt) > count;
357}
358
359/*
360 * check if the mount 'mnt' can be unmounted successfully.
361 * @mnt: the mount to be checked for unmount
362 * NOTE: unmounting 'mnt' would naturally propagate to all
363 * other mounts its parent propagates to.
364 * Check if any of these mounts that **do not have submounts**
365 * have more references than 'refcnt'. If so return busy.
366 *
367 * vfsmount lock must be held for write
368 */
369int propagate_mount_busy(struct mount *mnt, int refcnt)
370{
371	struct mount *m, *child, *topper;
372	struct mount *parent = mnt->mnt_parent;
373
374	if (mnt == parent)
375		return do_refcount_check(mnt, refcnt);
376
377	/*
378	 * quickly check if the current mount can be unmounted.
379	 * If not, we don't have to go checking for all other
380	 * mounts
381	 */
382	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
383		return 1;
384
385	for (m = propagation_next(parent, parent); m;
386	     		m = propagation_next(m, parent)) {
387		int count = 1;
388		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
389		if (!child)
390			continue;
391
392		/* Is there exactly one mount on the child that covers
393		 * it completely whose reference should be ignored?
394		 */
395		topper = find_topper(child);
396		if (topper)
397			count += 1;
398		else if (!list_empty(&child->mnt_mounts))
399			continue;
400
401		if (do_refcount_check(child, count))
402			return 1;
403	}
404	return 0;
405}
406
407/*
408 * Clear MNT_LOCKED when it can be shown to be safe.
409 *
410 * mount_lock lock must be held for write
411 */
412void propagate_mount_unlock(struct mount *mnt)
413{
414	struct mount *parent = mnt->mnt_parent;
415	struct mount *m, *child;
416
417	BUG_ON(parent == mnt);
418
419	for (m = propagation_next(parent, parent); m;
420			m = propagation_next(m, parent)) {
421		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
422		if (child)
423			child->mnt.mnt_flags &= ~MNT_LOCKED;
424	}
425}
426
427static void umount_one(struct mount *mnt, struct list_head *to_umount)
428{
429	CLEAR_MNT_MARK(mnt);
430	mnt->mnt.mnt_flags |= MNT_UMOUNT;
431	list_del_init(&mnt->mnt_child);
432	list_del_init(&mnt->mnt_umounting);
433	list_move_tail(&mnt->mnt_list, to_umount);
434}
435
436/*
437 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
438 * parent propagates to.
439 */
440static bool __propagate_umount(struct mount *mnt,
441			       struct list_head *to_umount,
442			       struct list_head *to_restore)
443{
444	bool progress = false;
445	struct mount *child;
446
447	/*
448	 * The state of the parent won't change if this mount is
449	 * already unmounted or marked as without children.
450	 */
451	if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
452		goto out;
453
454	/* Verify topper is the only grandchild that has not been
455	 * speculatively unmounted.
456	 */
457	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
458		if (child->mnt_mountpoint == mnt->mnt.mnt_root)
459			continue;
460		if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
461			continue;
462		/* Found a mounted child */
463		goto children;
464	}
465
466	/* Mark mounts that can be unmounted if not locked */
467	SET_MNT_MARK(mnt);
468	progress = true;
469
470	/* If a mount is without children and not locked umount it. */
471	if (!IS_MNT_LOCKED(mnt)) {
472		umount_one(mnt, to_umount);
473	} else {
474children:
475		list_move_tail(&mnt->mnt_umounting, to_restore);
476	}
477out:
478	return progress;
479}
480
481static void umount_list(struct list_head *to_umount,
482			struct list_head *to_restore)
483{
484	struct mount *mnt, *child, *tmp;
485	list_for_each_entry(mnt, to_umount, mnt_list) {
486		list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
487			/* topper? */
488			if (child->mnt_mountpoint == mnt->mnt.mnt_root)
489				list_move_tail(&child->mnt_umounting, to_restore);
490			else
491				umount_one(child, to_umount);
492		}
493	}
494}
495
496static void restore_mounts(struct list_head *to_restore)
497{
498	/* Restore mounts to a clean working state */
499	while (!list_empty(to_restore)) {
500		struct mount *mnt, *parent;
501		struct mountpoint *mp;
502
503		mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
504		CLEAR_MNT_MARK(mnt);
505		list_del_init(&mnt->mnt_umounting);
506
507		/* Should this mount be reparented? */
508		mp = mnt->mnt_mp;
509		parent = mnt->mnt_parent;
510		while (parent->mnt.mnt_flags & MNT_UMOUNT) {
511			mp = parent->mnt_mp;
512			parent = parent->mnt_parent;
513		}
514		if (parent != mnt->mnt_parent)
515			mnt_change_mountpoint(parent, mp, mnt);
516	}
517}
518
519static void cleanup_umount_visitations(struct list_head *visited)
520{
521	while (!list_empty(visited)) {
522		struct mount *mnt =
523			list_first_entry(visited, struct mount, mnt_umounting);
524		list_del_init(&mnt->mnt_umounting);
525	}
526}
527
528/*
529 * collect all mounts that receive propagation from the mount in @list,
530 * and return these additional mounts in the same list.
531 * @list: the list of mounts to be unmounted.
532 *
533 * vfsmount lock must be held for write
534 */
535int propagate_umount(struct list_head *list)
536{
537	struct mount *mnt;
538	LIST_HEAD(to_restore);
539	LIST_HEAD(to_umount);
540	LIST_HEAD(visited);
541
542	/* Find candidates for unmounting */
543	list_for_each_entry_reverse(mnt, list, mnt_list) {
544		struct mount *parent = mnt->mnt_parent;
545		struct mount *m;
546
547		/*
548		 * If this mount has already been visited it is known that it's
549		 * entire peer group and all of their slaves in the propagation
550		 * tree for the mountpoint has already been visited and there is
551		 * no need to visit them again.
552		 */
553		if (!list_empty(&mnt->mnt_umounting))
554			continue;
555
556		list_add_tail(&mnt->mnt_umounting, &visited);
557		for (m = propagation_next(parent, parent); m;
558		     m = propagation_next(m, parent)) {
559			struct mount *child = __lookup_mnt(&m->mnt,
560							   mnt->mnt_mountpoint);
561			if (!child)
562				continue;
563
564			if (!list_empty(&child->mnt_umounting)) {
565				/*
566				 * If the child has already been visited it is
567				 * know that it's entire peer group and all of
568				 * their slaves in the propgation tree for the
569				 * mountpoint has already been visited and there
570				 * is no need to visit this subtree again.
571				 */
572				m = skip_propagation_subtree(m, parent);
573				continue;
574			} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
575				/*
576				 * We have come accross an partially unmounted
577				 * mount in list that has not been visited yet.
578				 * Remember it has been visited and continue
579				 * about our merry way.
580				 */
581				list_add_tail(&child->mnt_umounting, &visited);
582				continue;
583			}
584
585			/* Check the child and parents while progress is made */
586			while (__propagate_umount(child,
587						  &to_umount, &to_restore)) {
588				/* Is the parent a umount candidate? */
589				child = child->mnt_parent;
590				if (list_empty(&child->mnt_umounting))
591					break;
592			}
593		}
594	}
595
596	umount_list(&to_umount, &to_restore);
597	restore_mounts(&to_restore);
598	cleanup_umount_visitations(&visited);
599	list_splice_tail(&to_umount, list);
600
601	return 0;
602}