641 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * linux/fs/pnode.c4 *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 representative56 * under the given root.57 *58 * Caller must hold namespace_sem59 */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 the97 * same root dentry. If none is available then98 * 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 write121 */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 else135 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;136 }137}138 139/*140 * get the next mount in the propagation tree.141 * @m: the mount seen last142 * @origin: the original mount from where the tree walk initiated143 *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 if146 * vfsmount found while iterating with propagation_next() is147 * 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 return175 * 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' at276 * dentry 'dest_dentry'. And propagate that mount to277 * all the peer and slave mounts of 'dest_mnt'.278 * Link all the new mounts into a propagation tree headed at279 * source_mnt. Also link all the new mounts using ->mnt_list280 * headed at source_mnt's ->mnt_list281 *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 to295 * 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 count351 */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 @from359 * would overmount @to360 * @from: shared mount361 * @to: mount to check362 * @mp: future mountpoint of @to on @from363 *364 * If @from propagates mounts to @to, @from and @to must either be peers365 * or one of the masters in the hierarchy of masters of @to must be a366 * peer of @from.367 *368 * If the root of the @to mount is equal to the future mountpoint @mp of369 * the @to mount on @from then @to will be overmounted by whatever is370 * propagated to it.371 *372 * Context: This function expects namespace_lock() to be held and that373 * @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 unmount400 * NOTE: unmounting 'mnt' would naturally propagate to all401 * 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 write406 */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 other418 * mounts419 */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 covers431 * 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 write449 */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 its476 * 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 is487 * 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 been493 * 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 else529 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 write572 */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's587 * entire peer group and all of their slaves in the propagation588 * tree for the mountpoint has already been visited and there is589 * 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 is605 * know that it's entire peer group and all of606 * their slaves in the propgation tree for the607 * mountpoint has already been visited and there608 * 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 unmounted615 * mount in list that has not been visited yet.616 * Remember it has been visited and continue617 * 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