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1 /*
2 * linux/fs/pnode.c
3 *
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
7 *
8 */
9 #include <linux/mnt_namespace.h>
10 #include <linux/mount.h>
11 #include <linux/fs.h>
12 #include <linux/nsproxy.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 *next_slave(struct mount *p)
28 {
29 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
30 }
31
32 static struct mount *get_peer_under_root(struct mount *mnt,
33 struct mnt_namespace *ns,
34 const struct path *root)
35 {
36 struct mount *m = mnt;
37
38 do {
39 /* Check the namespace first for optimization */
40 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
41 return m;
42
43 m = next_peer(m);
44 } while (m != mnt);
45
46 return NULL;
47 }
48
49 /*
50 * Get ID of closest dominating peer group having a representative
51 * under the given root.
52 *
53 * Caller must hold namespace_sem
54 */
55 int get_dominating_id(struct mount *mnt, const struct path *root)
56 {
57 struct mount *m;
58
59 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
60 struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
61 if (d)
62 return d->mnt_group_id;
63 }
64
65 return 0;
66 }
67
68 static int do_make_slave(struct mount *mnt)
69 {
70 struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
71 struct mount *slave_mnt;
72
73 /*
74 * slave 'mnt' to a peer mount that has the
75 * same root dentry. If none is available then
76 * slave it to anything that is available.
77 */
78 while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
79 peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
80
81 if (peer_mnt == mnt) {
82 peer_mnt = next_peer(mnt);
83 if (peer_mnt == mnt)
84 peer_mnt = NULL;
85 }
86 if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
87 list_empty(&mnt->mnt_share))
88 mnt_release_group_id(mnt);
89
90 list_del_init(&mnt->mnt_share);
91 mnt->mnt_group_id = 0;
92
93 if (peer_mnt)
94 master = peer_mnt;
95
96 if (master) {
97 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
98 slave_mnt->mnt_master = master;
99 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
100 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
101 INIT_LIST_HEAD(&mnt->mnt_slave_list);
102 } else {
103 struct list_head *p = &mnt->mnt_slave_list;
104 while (!list_empty(p)) {
105 slave_mnt = list_first_entry(p,
106 struct mount, mnt_slave);
107 list_del_init(&slave_mnt->mnt_slave);
108 slave_mnt->mnt_master = NULL;
109 }
110 }
111 mnt->mnt_master = master;
112 CLEAR_MNT_SHARED(mnt);
113 return 0;
114 }
115
116 /*
117 * vfsmount lock must be held for write
118 */
119 void change_mnt_propagation(struct mount *mnt, int type)
120 {
121 if (type == MS_SHARED) {
122 set_mnt_shared(mnt);
123 return;
124 }
125 do_make_slave(mnt);
126 if (type != MS_SLAVE) {
127 list_del_init(&mnt->mnt_slave);
128 mnt->mnt_master = NULL;
129 if (type == MS_UNBINDABLE)
130 mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
131 else
132 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
133 }
134 }
135
136 /*
137 * get the next mount in the propagation tree.
138 * @m: the mount seen last
139 * @origin: the original mount from where the tree walk initiated
140 *
141 * Note that peer groups form contiguous segments of slave lists.
142 * We rely on that in get_source() to be able to find out if
143 * vfsmount found while iterating with propagation_next() is
144 * a peer of one we'd found earlier.
145 */
146 static struct mount *propagation_next(struct mount *m,
147 struct mount *origin)
148 {
149 /* are there any slaves of this mount? */
150 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
151 return first_slave(m);
152
153 while (1) {
154 struct mount *master = m->mnt_master;
155
156 if (master == origin->mnt_master) {
157 struct mount *next = next_peer(m);
158 return (next == origin) ? NULL : next;
159 } else if (m->mnt_slave.next != &master->mnt_slave_list)
160 return next_slave(m);
161
162 /* back at master */
163 m = master;
164 }
165 }
166
167 static struct mount *next_group(struct mount *m, struct mount *origin)
168 {
169 while (1) {
170 while (1) {
171 struct mount *next;
172 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
173 return first_slave(m);
174 next = next_peer(m);
175 if (m->mnt_group_id == origin->mnt_group_id) {
176 if (next == origin)
177 return NULL;
178 } else if (m->mnt_slave.next != &next->mnt_slave)
179 break;
180 m = next;
181 }
182 /* m is the last peer */
183 while (1) {
184 struct mount *master = m->mnt_master;
185 if (m->mnt_slave.next != &master->mnt_slave_list)
186 return next_slave(m);
187 m = next_peer(master);
188 if (master->mnt_group_id == origin->mnt_group_id)
189 break;
190 if (master->mnt_slave.next == &m->mnt_slave)
191 break;
192 m = master;
193 }
194 if (m == origin)
195 return NULL;
196 }
197 }
198
199 /* all accesses are serialized by namespace_sem */
200 static struct user_namespace *user_ns;
201 static struct mount *last_dest, *last_source, *dest_master;
202 static struct mountpoint *mp;
203 static struct hlist_head *list;
204
205 static int propagate_one(struct mount *m)
206 {
207 struct mount *child;
208 int type;
209 /* skip ones added by this propagate_mnt() */
210 if (IS_MNT_NEW(m))
211 return 0;
212 /* skip if mountpoint isn't covered by it */
213 if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
214 return 0;
215 if (m->mnt_group_id == last_dest->mnt_group_id) {
216 type = CL_MAKE_SHARED;
217 } else {
218 struct mount *n, *p;
219 for (n = m; ; n = p) {
220 p = n->mnt_master;
221 if (p == dest_master || IS_MNT_MARKED(p)) {
222 while (last_dest->mnt_master != p) {
223 last_source = last_source->mnt_master;
224 last_dest = last_source->mnt_parent;
225 }
226 if (n->mnt_group_id != last_dest->mnt_group_id) {
227 last_source = last_source->mnt_master;
228 last_dest = last_source->mnt_parent;
229 }
230 break;
231 }
232 }
233 type = CL_SLAVE;
234 /* beginning of peer group among the slaves? */
235 if (IS_MNT_SHARED(m))
236 type |= CL_MAKE_SHARED;
237 }
238
239 /* Notice when we are propagating across user namespaces */
240 if (m->mnt_ns->user_ns != user_ns)
241 type |= CL_UNPRIVILEGED;
242 child = copy_tree(last_source, last_source->mnt.mnt_root, type);
243 if (IS_ERR(child))
244 return PTR_ERR(child);
245 child->mnt.mnt_flags &= ~MNT_LOCKED;
246 mnt_set_mountpoint(m, mp, child);
247 last_dest = m;
248 last_source = child;
249 if (m->mnt_master != dest_master) {
250 read_seqlock_excl(&mount_lock);
251 SET_MNT_MARK(m->mnt_master);
252 read_sequnlock_excl(&mount_lock);
253 }
254 hlist_add_head(&child->mnt_hash, list);
255 return 0;
256 }
257
258 /*
259 * mount 'source_mnt' under the destination 'dest_mnt' at
260 * dentry 'dest_dentry'. And propagate that mount to
261 * all the peer and slave mounts of 'dest_mnt'.
262 * Link all the new mounts into a propagation tree headed at
263 * source_mnt. Also link all the new mounts using ->mnt_list
264 * headed at source_mnt's ->mnt_list
265 *
266 * @dest_mnt: destination mount.
267 * @dest_dentry: destination dentry.
268 * @source_mnt: source mount.
269 * @tree_list : list of heads of trees to be attached.
270 */
271 int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
272 struct mount *source_mnt, struct hlist_head *tree_list)
273 {
274 struct mount *m, *n;
275 int ret = 0;
276
277 /*
278 * we don't want to bother passing tons of arguments to
279 * propagate_one(); everything is serialized by namespace_sem,
280 * so globals will do just fine.
281 */
282 user_ns = current->nsproxy->mnt_ns->user_ns;
283 last_dest = dest_mnt;
284 last_source = source_mnt;
285 mp = dest_mp;
286 list = tree_list;
287 dest_master = dest_mnt->mnt_master;
288
289 /* all peers of dest_mnt, except dest_mnt itself */
290 for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
291 ret = propagate_one(n);
292 if (ret)
293 goto out;
294 }
295
296 /* all slave groups */
297 for (m = next_group(dest_mnt, dest_mnt); m;
298 m = next_group(m, dest_mnt)) {
299 /* everything in that slave group */
300 n = m;
301 do {
302 ret = propagate_one(n);
303 if (ret)
304 goto out;
305 n = next_peer(n);
306 } while (n != m);
307 }
308 out:
309 read_seqlock_excl(&mount_lock);
310 hlist_for_each_entry(n, tree_list, mnt_hash) {
311 m = n->mnt_parent;
312 if (m->mnt_master != dest_mnt->mnt_master)
313 CLEAR_MNT_MARK(m->mnt_master);
314 }
315 read_sequnlock_excl(&mount_lock);
316 return ret;
317 }
318
319 /*
320 * return true if the refcount is greater than count
321 */
322 static inline int do_refcount_check(struct mount *mnt, int count)
323 {
324 return mnt_get_count(mnt) > count;
325 }
326
327 /*
328 * check if the mount 'mnt' can be unmounted successfully.
329 * @mnt: the mount to be checked for unmount
330 * NOTE: unmounting 'mnt' would naturally propagate to all
331 * other mounts its parent propagates to.
332 * Check if any of these mounts that **do not have submounts**
333 * have more references than 'refcnt'. If so return busy.
334 *
335 * vfsmount lock must be held for write
336 */
337 int propagate_mount_busy(struct mount *mnt, int refcnt)
338 {
339 struct mount *m, *child;
340 struct mount *parent = mnt->mnt_parent;
341 int ret = 0;
342
343 if (mnt == parent)
344 return do_refcount_check(mnt, refcnt);
345
346 /*
347 * quickly check if the current mount can be unmounted.
348 * If not, we don't have to go checking for all other
349 * mounts
350 */
351 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
352 return 1;
353
354 for (m = propagation_next(parent, parent); m;
355 m = propagation_next(m, parent)) {
356 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
357 if (child && list_empty(&child->mnt_mounts) &&
358 (ret = do_refcount_check(child, 1)))
359 break;
360 }
361 return ret;
362 }
363
364 /*
365 * Clear MNT_LOCKED when it can be shown to be safe.
366 *
367 * mount_lock lock must be held for write
368 */
369 void propagate_mount_unlock(struct mount *mnt)
370 {
371 struct mount *parent = mnt->mnt_parent;
372 struct mount *m, *child;
373
374 BUG_ON(parent == mnt);
375
376 for (m = propagation_next(parent, parent); m;
377 m = propagation_next(m, parent)) {
378 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
379 if (child)
380 child->mnt.mnt_flags &= ~MNT_LOCKED;
381 }
382 }
383
384 /*
385 * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
386 */
387 static void mark_umount_candidates(struct mount *mnt)
388 {
389 struct mount *parent = mnt->mnt_parent;
390 struct mount *m;
391
392 BUG_ON(parent == mnt);
393
394 for (m = propagation_next(parent, parent); m;
395 m = propagation_next(m, parent)) {
396 struct mount *child = __lookup_mnt_last(&m->mnt,
397 mnt->mnt_mountpoint);
398 if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
399 SET_MNT_MARK(child);
400 }
401 }
402 }
403
404 /*
405 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
406 * parent propagates to.
407 */
408 static void __propagate_umount(struct mount *mnt)
409 {
410 struct mount *parent = mnt->mnt_parent;
411 struct mount *m;
412
413 BUG_ON(parent == mnt);
414
415 for (m = propagation_next(parent, parent); m;
416 m = propagation_next(m, parent)) {
417
418 struct mount *child = __lookup_mnt_last(&m->mnt,
419 mnt->mnt_mountpoint);
420 /*
421 * umount the child only if the child has no children
422 * and the child is marked safe to unmount.
423 */
424 if (!child || !IS_MNT_MARKED(child))
425 continue;
426 CLEAR_MNT_MARK(child);
427 if (list_empty(&child->mnt_mounts)) {
428 list_del_init(&child->mnt_child);
429 child->mnt.mnt_flags |= MNT_UMOUNT;
430 list_move_tail(&child->mnt_list, &mnt->mnt_list);
431 }
432 }
433 }
434
435 /*
436 * collect all mounts that receive propagation from the mount in @list,
437 * and return these additional mounts in the same list.
438 * @list: the list of mounts to be unmounted.
439 *
440 * vfsmount lock must be held for write
441 */
442 int propagate_umount(struct list_head *list)
443 {
444 struct mount *mnt;
445
446 list_for_each_entry_reverse(mnt, list, mnt_list)
447 mark_umount_candidates(mnt);
448
449 list_for_each_entry(mnt, list, mnt_list)
450 __propagate_umount(mnt);
451 return 0;
452 }