Line data Source code
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 0 : 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 0 : 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 0 : 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 0 : return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
35 : }
36 :
37 0 : static struct mount *get_peer_under_root(struct mount *mnt,
38 : struct mnt_namespace *ns,
39 : const struct path *root)
40 : {
41 0 : struct mount *m = mnt;
42 :
43 : do {
44 : /* Check the namespace first for optimization */
45 0 : if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
46 : return m;
47 :
48 0 : m = next_peer(m);
49 0 : } 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 0 : int get_dominating_id(struct mount *mnt, const struct path *root)
61 : {
62 : struct mount *m;
63 :
64 0 : for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
65 0 : struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
66 0 : if (d)
67 0 : return d->mnt_group_id;
68 : }
69 :
70 : return 0;
71 : }
72 :
73 0 : static int do_make_slave(struct mount *mnt)
74 : {
75 : struct mount *master, *slave_mnt;
76 :
77 0 : if (list_empty(&mnt->mnt_share)) {
78 0 : if (IS_MNT_SHARED(mnt)) {
79 0 : mnt_release_group_id(mnt);
80 0 : CLEAR_MNT_SHARED(mnt);
81 : }
82 0 : master = mnt->mnt_master;
83 0 : if (!master) {
84 0 : struct list_head *p = &mnt->mnt_slave_list;
85 0 : while (!list_empty(p)) {
86 0 : slave_mnt = list_first_entry(p,
87 : struct mount, mnt_slave);
88 0 : list_del_init(&slave_mnt->mnt_slave);
89 0 : 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 0 : for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
101 0 : if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
102 : master = m;
103 : break;
104 : }
105 : }
106 0 : list_del_init(&mnt->mnt_share);
107 0 : mnt->mnt_group_id = 0;
108 0 : CLEAR_MNT_SHARED(mnt);
109 : }
110 0 : list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
111 0 : slave_mnt->mnt_master = master;
112 0 : list_move(&mnt->mnt_slave, &master->mnt_slave_list);
113 0 : list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
114 0 : INIT_LIST_HEAD(&mnt->mnt_slave_list);
115 0 : mnt->mnt_master = master;
116 0 : return 0;
117 : }
118 :
119 : /*
120 : * vfsmount lock must be held for write
121 : */
122 0 : void change_mnt_propagation(struct mount *mnt, int type)
123 : {
124 0 : if (type == MS_SHARED) {
125 0 : set_mnt_shared(mnt);
126 : return;
127 : }
128 0 : do_make_slave(mnt);
129 0 : if (type != MS_SLAVE) {
130 0 : list_del_init(&mnt->mnt_slave);
131 0 : mnt->mnt_master = NULL;
132 0 : if (type == MS_UNBINDABLE)
133 0 : mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
134 : else
135 0 : 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 0 : static struct mount *propagation_next(struct mount *m,
150 : struct mount *origin)
151 : {
152 : /* are there any slaves of this mount? */
153 0 : if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
154 0 : return first_slave(m);
155 :
156 : while (1) {
157 0 : struct mount *master = m->mnt_master;
158 :
159 0 : if (master == origin->mnt_master) {
160 0 : struct mount *next = next_peer(m);
161 0 : return (next == origin) ? NULL : next;
162 0 : } else if (m->mnt_slave.next != &master->mnt_slave_list)
163 0 : 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 0 : if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
178 0 : m = last_slave(m);
179 :
180 : return m;
181 : }
182 :
183 0 : static struct mount *next_group(struct mount *m, struct mount *origin)
184 : {
185 : while (1) {
186 : while (1) {
187 : struct mount *next;
188 0 : if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
189 0 : return first_slave(m);
190 0 : next = next_peer(m);
191 0 : if (m->mnt_group_id == origin->mnt_group_id) {
192 0 : if (next == origin)
193 : return NULL;
194 0 : } 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 0 : struct mount *master = m->mnt_master;
201 0 : if (m->mnt_slave.next != &master->mnt_slave_list)
202 0 : return next_slave(m);
203 0 : m = next_peer(master);
204 0 : if (master->mnt_group_id == origin->mnt_group_id)
205 : break;
206 0 : if (master->mnt_slave.next == &m->mnt_slave)
207 : break;
208 : m = master;
209 : }
210 0 : 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 0 : return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
222 : }
223 :
224 0 : 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 0 : if (IS_MNT_NEW(m))
230 : return 0;
231 : /* skip if mountpoint isn't covered by it */
232 0 : if (!is_subdir(dest_mp->m_dentry, m->mnt.mnt_root))
233 : return 0;
234 0 : 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 0 : p = n->mnt_master;
241 0 : if (p == dest_master || IS_MNT_MARKED(p))
242 : break;
243 : }
244 : do {
245 0 : struct mount *parent = last_source->mnt_parent;
246 0 : if (peers(last_source, first_source))
247 : break;
248 0 : done = parent->mnt_master == p;
249 0 : if (done && peers(n, parent))
250 : break;
251 0 : last_source = last_source->mnt_master;
252 0 : } while (!done);
253 :
254 0 : type = CL_SLAVE;
255 : /* beginning of peer group among the slaves? */
256 0 : if (IS_MNT_SHARED(m))
257 0 : type |= CL_MAKE_SHARED;
258 : }
259 :
260 0 : child = copy_tree(last_source, last_source->mnt.mnt_root, type);
261 0 : if (IS_ERR(child))
262 0 : return PTR_ERR(child);
263 0 : read_seqlock_excl(&mount_lock);
264 0 : mnt_set_mountpoint(m, dest_mp, child);
265 0 : if (m->mnt_master != dest_master)
266 0 : SET_MNT_MARK(m->mnt_master);
267 0 : read_sequnlock_excl(&mount_lock);
268 0 : last_dest = m;
269 0 : last_source = child;
270 0 : hlist_add_head(&child->mnt_hash, list);
271 0 : 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 0 : 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 0 : 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 0 : last_dest = dest_mnt;
299 0 : first_source = source_mnt;
300 0 : last_source = source_mnt;
301 0 : list = tree_list;
302 0 : dest_master = dest_mnt->mnt_master;
303 :
304 : /* all peers of dest_mnt, except dest_mnt itself */
305 0 : for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
306 0 : ret = propagate_one(n, dest_mp);
307 0 : if (ret)
308 : goto out;
309 : }
310 :
311 : /* all slave groups */
312 0 : for (m = next_group(dest_mnt, dest_mnt); m;
313 0 : m = next_group(m, dest_mnt)) {
314 : /* everything in that slave group */
315 : n = m;
316 : do {
317 0 : ret = propagate_one(n, dest_mp);
318 0 : if (ret)
319 : goto out;
320 0 : n = next_peer(n);
321 0 : } while (n != m);
322 : }
323 : out:
324 0 : read_seqlock_excl(&mount_lock);
325 0 : hlist_for_each_entry(n, tree_list, mnt_hash) {
326 0 : m = n->mnt_parent;
327 0 : if (m->mnt_master != dest_mnt->mnt_master)
328 0 : CLEAR_MNT_MARK(m->mnt_master);
329 : }
330 0 : read_sequnlock_excl(&mount_lock);
331 0 : 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 0 : if (!list_is_singular(&mnt->mnt_mounts))
340 : return NULL;
341 :
342 0 : child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
343 0 : 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 0 : 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 0 : bool propagation_would_overmount(const struct mount *from,
377 : const struct mount *to,
378 : const struct mountpoint *mp)
379 : {
380 0 : if (!IS_MNT_SHARED(from))
381 : return false;
382 :
383 0 : if (IS_MNT_NEW(to))
384 : return false;
385 :
386 0 : if (to->mnt.mnt_root != mp->m_dentry)
387 : return false;
388 :
389 0 : for (const struct mount *m = to; m; m = m->mnt_master) {
390 0 : 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 0 : int propagate_mount_busy(struct mount *mnt, int refcnt)
408 : {
409 : struct mount *m, *child, *topper;
410 0 : struct mount *parent = mnt->mnt_parent;
411 :
412 0 : if (mnt == parent)
413 0 : 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 0 : if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
421 : return 1;
422 :
423 0 : for (m = propagation_next(parent, parent); m;
424 0 : m = propagation_next(m, parent)) {
425 0 : int count = 1;
426 0 : child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
427 0 : if (!child)
428 0 : continue;
429 :
430 : /* Is there exactly one mount on the child that covers
431 : * it completely whose reference should be ignored?
432 : */
433 0 : topper = find_topper(child);
434 0 : if (topper)
435 : count += 1;
436 0 : else if (!list_empty(&child->mnt_mounts))
437 0 : continue;
438 :
439 0 : 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 0 : void propagate_mount_unlock(struct mount *mnt)
451 : {
452 0 : struct mount *parent = mnt->mnt_parent;
453 : struct mount *m, *child;
454 :
455 0 : BUG_ON(parent == mnt);
456 :
457 0 : for (m = propagation_next(parent, parent); m;
458 0 : m = propagation_next(m, parent)) {
459 0 : child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
460 0 : if (child)
461 0 : child->mnt.mnt_flags &= ~MNT_LOCKED;
462 : }
463 0 : }
464 :
465 : static void umount_one(struct mount *mnt, struct list_head *to_umount)
466 : {
467 0 : CLEAR_MNT_MARK(mnt);
468 0 : mnt->mnt.mnt_flags |= MNT_UMOUNT;
469 0 : list_del_init(&mnt->mnt_child);
470 0 : list_del_init(&mnt->mnt_umounting);
471 0 : list_move_tail(&mnt->mnt_list, to_umount);
472 : }
473 :
474 : /*
475 : * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
476 : * parent propagates to.
477 : */
478 0 : static bool __propagate_umount(struct mount *mnt,
479 : struct list_head *to_umount,
480 : struct list_head *to_restore)
481 : {
482 0 : 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 0 : 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 0 : list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
496 0 : if (child->mnt_mountpoint == mnt->mnt.mnt_root)
497 0 : continue;
498 0 : if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
499 0 : continue;
500 : /* Found a mounted child */
501 : goto children;
502 : }
503 :
504 : /* Mark mounts that can be unmounted if not locked */
505 0 : SET_MNT_MARK(mnt);
506 0 : progress = true;
507 :
508 : /* If a mount is without children and not locked umount it. */
509 0 : if (!IS_MNT_LOCKED(mnt)) {
510 : umount_one(mnt, to_umount);
511 : } else {
512 : children:
513 0 : list_move_tail(&mnt->mnt_umounting, to_restore);
514 : }
515 : out:
516 0 : return progress;
517 : }
518 :
519 0 : static void umount_list(struct list_head *to_umount,
520 : struct list_head *to_restore)
521 : {
522 : struct mount *mnt, *child, *tmp;
523 0 : list_for_each_entry(mnt, to_umount, mnt_list) {
524 0 : list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
525 : /* topper? */
526 0 : if (child->mnt_mountpoint == mnt->mnt.mnt_root)
527 0 : list_move_tail(&child->mnt_umounting, to_restore);
528 : else
529 : umount_one(child, to_umount);
530 : }
531 : }
532 0 : }
533 :
534 0 : static void restore_mounts(struct list_head *to_restore)
535 : {
536 : /* Restore mounts to a clean working state */
537 0 : while (!list_empty(to_restore)) {
538 : struct mount *mnt, *parent;
539 : struct mountpoint *mp;
540 :
541 0 : mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
542 0 : CLEAR_MNT_MARK(mnt);
543 0 : list_del_init(&mnt->mnt_umounting);
544 :
545 : /* Should this mount be reparented? */
546 0 : mp = mnt->mnt_mp;
547 0 : parent = mnt->mnt_parent;
548 0 : while (parent->mnt.mnt_flags & MNT_UMOUNT) {
549 0 : mp = parent->mnt_mp;
550 0 : parent = parent->mnt_parent;
551 : }
552 0 : if (parent != mnt->mnt_parent)
553 0 : mnt_change_mountpoint(parent, mp, mnt);
554 : }
555 0 : }
556 :
557 : static void cleanup_umount_visitations(struct list_head *visited)
558 : {
559 0 : while (!list_empty(visited)) {
560 0 : struct mount *mnt =
561 0 : list_first_entry(visited, struct mount, mnt_umounting);
562 0 : 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 0 : int propagate_umount(struct list_head *list)
574 : {
575 : struct mount *mnt;
576 0 : LIST_HEAD(to_restore);
577 0 : LIST_HEAD(to_umount);
578 0 : LIST_HEAD(visited);
579 :
580 : /* Find candidates for unmounting */
581 0 : list_for_each_entry_reverse(mnt, list, mnt_list) {
582 0 : 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 0 : if (!list_empty(&mnt->mnt_umounting))
592 0 : continue;
593 :
594 0 : list_add_tail(&mnt->mnt_umounting, &visited);
595 0 : for (m = propagation_next(parent, parent); m;
596 0 : m = propagation_next(m, parent)) {
597 0 : struct mount *child = __lookup_mnt(&m->mnt,
598 : mnt->mnt_mountpoint);
599 0 : if (!child)
600 0 : continue;
601 :
602 0 : 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 0 : m = skip_propagation_subtree(m, parent);
611 0 : continue;
612 0 : } 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 0 : list_add_tail(&child->mnt_umounting, &visited);
620 0 : continue;
621 : }
622 :
623 : /* Check the child and parents while progress is made */
624 0 : while (__propagate_umount(child,
625 : &to_umount, &to_restore)) {
626 : /* Is the parent a umount candidate? */
627 0 : child = child->mnt_parent;
628 0 : if (list_empty(&child->mnt_umounting))
629 : break;
630 : }
631 : }
632 : }
633 :
634 0 : umount_list(&to_umount, &to_restore);
635 0 : restore_mounts(&to_restore);
636 0 : cleanup_umount_visitations(&visited);
637 0 : list_splice_tail(&to_umount, list);
638 :
639 0 : return 0;
640 : }
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