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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 | /* |
168 | * return the source mount to be used for cloning |
169 | * |
170 | * @dest the current destination mount |
171 | * @last_dest the last seen destination mount |
172 | * @last_src the last seen source mount |
173 | * @type return CL_SLAVE if the new mount has to be |
174 | * cloned as a slave. |
175 | */ |
176 | static struct mount *get_source(struct mount *dest, |
177 | struct mount *last_dest, |
178 | struct mount *last_src, |
179 | int *type) |
180 | { |
181 | struct mount *p_last_src = NULL; |
182 | struct mount *p_last_dest = NULL; |
183 | |
184 | while (last_dest != dest->mnt_master) { |
185 | p_last_dest = last_dest; |
186 | p_last_src = last_src; |
187 | last_dest = last_dest->mnt_master; |
188 | last_src = last_src->mnt_master; |
189 | } |
190 | |
191 | if (p_last_dest) { |
192 | do { |
193 | p_last_dest = next_peer(p_last_dest); |
194 | } while (IS_MNT_NEW(p_last_dest)); |
195 | /* is that a peer of the earlier? */ |
196 | if (dest == p_last_dest) { |
197 | *type = CL_MAKE_SHARED; |
198 | return p_last_src; |
199 | } |
200 | } |
201 | /* slave of the earlier, then */ |
202 | *type = CL_SLAVE; |
203 | /* beginning of peer group among the slaves? */ |
204 | if (IS_MNT_SHARED(dest)) |
205 | *type |= CL_MAKE_SHARED; |
206 | return last_src; |
207 | } |
208 | |
209 | /* |
210 | * mount 'source_mnt' under the destination 'dest_mnt' at |
211 | * dentry 'dest_dentry'. And propagate that mount to |
212 | * all the peer and slave mounts of 'dest_mnt'. |
213 | * Link all the new mounts into a propagation tree headed at |
214 | * source_mnt. Also link all the new mounts using ->mnt_list |
215 | * headed at source_mnt's ->mnt_list |
216 | * |
217 | * @dest_mnt: destination mount. |
218 | * @dest_dentry: destination dentry. |
219 | * @source_mnt: source mount. |
220 | * @tree_list : list of heads of trees to be attached. |
221 | */ |
222 | int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp, |
223 | struct mount *source_mnt, struct list_head *tree_list) |
224 | { |
225 | struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns; |
226 | struct mount *m, *child; |
227 | int ret = 0; |
228 | struct mount *prev_dest_mnt = dest_mnt; |
229 | struct mount *prev_src_mnt = source_mnt; |
230 | LIST_HEAD(tmp_list); |
231 | |
232 | for (m = propagation_next(dest_mnt, dest_mnt); m; |
233 | m = propagation_next(m, dest_mnt)) { |
234 | int type; |
235 | struct mount *source; |
236 | |
237 | if (IS_MNT_NEW(m)) |
238 | continue; |
239 | |
240 | source = get_source(m, prev_dest_mnt, prev_src_mnt, &type); |
241 | |
242 | /* Notice when we are propagating across user namespaces */ |
243 | if (m->mnt_ns->user_ns != user_ns) |
244 | type |= CL_UNPRIVILEGED; |
245 | |
246 | child = copy_tree(source, source->mnt.mnt_root, type); |
247 | if (IS_ERR(child)) { |
248 | ret = PTR_ERR(child); |
249 | list_splice(tree_list, tmp_list.prev); |
250 | goto out; |
251 | } |
252 | |
253 | if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) { |
254 | mnt_set_mountpoint(m, dest_mp, child); |
255 | list_add_tail(&child->mnt_hash, tree_list); |
256 | } else { |
257 | /* |
258 | * This can happen if the parent mount was bind mounted |
259 | * on some subdirectory of a shared/slave mount. |
260 | */ |
261 | list_add_tail(&child->mnt_hash, &tmp_list); |
262 | } |
263 | prev_dest_mnt = m; |
264 | prev_src_mnt = child; |
265 | } |
266 | out: |
267 | br_write_lock(&vfsmount_lock); |
268 | while (!list_empty(&tmp_list)) { |
269 | child = list_first_entry(&tmp_list, struct mount, mnt_hash); |
270 | umount_tree(child, 0); |
271 | } |
272 | br_write_unlock(&vfsmount_lock); |
273 | return ret; |
274 | } |
275 | |
276 | /* |
277 | * return true if the refcount is greater than count |
278 | */ |
279 | static inline int do_refcount_check(struct mount *mnt, int count) |
280 | { |
281 | int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts; |
282 | return (mycount > count); |
283 | } |
284 | |
285 | /* |
286 | * check if the mount 'mnt' can be unmounted successfully. |
287 | * @mnt: the mount to be checked for unmount |
288 | * NOTE: unmounting 'mnt' would naturally propagate to all |
289 | * other mounts its parent propagates to. |
290 | * Check if any of these mounts that **do not have submounts** |
291 | * have more references than 'refcnt'. If so return busy. |
292 | * |
293 | * vfsmount lock must be held for write |
294 | */ |
295 | int propagate_mount_busy(struct mount *mnt, int refcnt) |
296 | { |
297 | struct mount *m, *child; |
298 | struct mount *parent = mnt->mnt_parent; |
299 | int ret = 0; |
300 | |
301 | if (mnt == parent) |
302 | return do_refcount_check(mnt, refcnt); |
303 | |
304 | /* |
305 | * quickly check if the current mount can be unmounted. |
306 | * If not, we don't have to go checking for all other |
307 | * mounts |
308 | */ |
309 | if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt)) |
310 | return 1; |
311 | |
312 | for (m = propagation_next(parent, parent); m; |
313 | m = propagation_next(m, parent)) { |
314 | child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint, 0); |
315 | if (child && list_empty(&child->mnt_mounts) && |
316 | (ret = do_refcount_check(child, 1))) |
317 | break; |
318 | } |
319 | return ret; |
320 | } |
321 | |
322 | /* |
323 | * NOTE: unmounting 'mnt' naturally propagates to all other mounts its |
324 | * parent propagates to. |
325 | */ |
326 | static void __propagate_umount(struct mount *mnt) |
327 | { |
328 | struct mount *parent = mnt->mnt_parent; |
329 | struct mount *m; |
330 | |
331 | BUG_ON(parent == mnt); |
332 | |
333 | for (m = propagation_next(parent, parent); m; |
334 | m = propagation_next(m, parent)) { |
335 | |
336 | struct mount *child = __lookup_mnt(&m->mnt, |
337 | mnt->mnt_mountpoint, 0); |
338 | /* |
339 | * umount the child only if the child has no |
340 | * other children |
341 | */ |
342 | if (child && list_empty(&child->mnt_mounts)) |
343 | list_move_tail(&child->mnt_hash, &mnt->mnt_hash); |
344 | } |
345 | } |
346 | |
347 | /* |
348 | * collect all mounts that receive propagation from the mount in @list, |
349 | * and return these additional mounts in the same list. |
350 | * @list: the list of mounts to be unmounted. |
351 | * |
352 | * vfsmount lock must be held for write |
353 | */ |
354 | int propagate_umount(struct list_head *list) |
355 | { |
356 | struct mount *mnt; |
357 | |
358 | list_for_each_entry(mnt, list, mnt_hash) |
359 | __propagate_umount(mnt); |
360 | return 0; |
361 | } |
362 |
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