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 */
17 static inline struct mount *next_peer(struct mount *p)
18 {
19 return list_entry(p->mnt_share.next, struct mount, mnt_share);
20 }
21
22 static inline struct mount *first_slave(struct mount *p)
23 {
24 return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
25 }
26
27 static inline struct mount *last_slave(struct mount *p)
28 {
29 return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
30 }
31
32 static inline struct mount *next_slave(struct mount *p)
33 {
34 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
35 }
36
37 static 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 */
60 int 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
73 static 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 */
122 void 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 */
149 static 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
170 static 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
183 static 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 */
216 static struct mount *last_dest, *first_source, *last_source, *dest_master;
217 static struct hlist_head *list;
218
219 static 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
224 static 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 */
287 int 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 }
323 out:
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
334 static 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 */
352 static 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 */
376 bool 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 */
407 int 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 */
450 void 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
465 static 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 */
478 static 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 {
512 children:
513 list_move_tail(&mnt->mnt_umounting, to_restore);
514 }
515 out:
516 return progress;
517 }
518
519 static 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
534 static 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
557 static 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 */
573 int 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
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