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 (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share)) 87 mnt_release_group_id(mnt); 88 89 list_del_init(&mnt->mnt_share); 90 mnt->mnt_group_id = 0; 91 92 if (peer_mnt) 93 master = peer_mnt; 94 95 if (master) { 96 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave) 97 slave_mnt->mnt_master = master; 98 list_move(&mnt->mnt_slave, &master->mnt_slave_list); 99 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev); 100 INIT_LIST_HEAD(&mnt->mnt_slave_list); 101 } else { 102 struct list_head *p = &mnt->mnt_slave_list; 103 while (!list_empty(p)) { 104 slave_mnt = list_first_entry(p, 105 struct mount, mnt_slave); 106 list_del_init(&slave_mnt->mnt_slave); 107 slave_mnt->mnt_master = NULL; 108 } 109 } 110 mnt->mnt_master = master; 111 CLEAR_MNT_SHARED(mnt); 112 return 0; 113 } 114 115 /* 116 * vfsmount lock must be held for write 117 */ 118 void change_mnt_propagation(struct mount *mnt, int type) 119 { 120 if (type == MS_SHARED) { 121 set_mnt_shared(mnt); 122 return; 123 } 124 do_make_slave(mnt); 125 if (type != MS_SLAVE) { 126 list_del_init(&mnt->mnt_slave); 127 mnt->mnt_master = NULL; 128 if (type == MS_UNBINDABLE) 129 mnt->mnt.mnt_flags |= MNT_UNBINDABLE; 130 else 131 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE; 132 } 133 } 134 135 /* 136 * get the next mount in the propagation tree. 137 * @m: the mount seen last 138 * @origin: the original mount from where the tree walk initiated 139 * 140 * Note that peer groups form contiguous segments of slave lists. 141 * We rely on that in get_source() to be able to find out if 142 * vfsmount found while iterating with propagation_next() is 143 * a peer of one we'd found earlier. 144 */ 145 static struct mount *propagation_next(struct mount *m, 146 struct mount *origin) 147 { 148 /* are there any slaves of this mount? */ 149 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list)) 150 return first_slave(m); 151 152 while (1) { 153 struct mount *master = m->mnt_master; 154 155 if (master == origin->mnt_master) { 156 struct mount *next = next_peer(m); 157 return (next == origin) ? NULL : next; 158 } else if (m->mnt_slave.next != &master->mnt_slave_list) 159 return next_slave(m); 160 161 /* back at master */ 162 m = master; 163 } 164 } 165 166 /* 167 * return the source mount to be used for cloning 168 * 169 * @dest the current destination mount 170 * @last_dest the last seen destination mount 171 * @last_src the last seen source mount 172 * @type return CL_SLAVE if the new mount has to be 173 * cloned as a slave. 174 */ 175 static struct mount *get_source(struct mount *dest, 176 struct mount *last_dest, 177 struct mount *last_src, 178 int *type) 179 { 180 struct mount *p_last_src = NULL; 181 struct mount *p_last_dest = NULL; 182 183 while (last_dest != dest->mnt_master) { 184 p_last_dest = last_dest; 185 p_last_src = last_src; 186 last_dest = last_dest->mnt_master; 187 last_src = last_src->mnt_master; 188 } 189 190 if (p_last_dest) { 191 do { 192 p_last_dest = next_peer(p_last_dest); 193 } while (IS_MNT_NEW(p_last_dest)); 194 /* is that a peer of the earlier? */ 195 if (dest == p_last_dest) { 196 *type = CL_MAKE_SHARED; 197 return p_last_src; 198 } 199 } 200 /* slave of the earlier, then */ 201 *type = CL_SLAVE; 202 /* beginning of peer group among the slaves? */ 203 if (IS_MNT_SHARED(dest)) 204 *type |= CL_MAKE_SHARED; 205 return last_src; 206 } 207 208 /* 209 * mount 'source_mnt' under the destination 'dest_mnt' at 210 * dentry 'dest_dentry'. And propagate that mount to 211 * all the peer and slave mounts of 'dest_mnt'. 212 * Link all the new mounts into a propagation tree headed at 213 * source_mnt. Also link all the new mounts using ->mnt_list 214 * headed at source_mnt's ->mnt_list 215 * 216 * @dest_mnt: destination mount. 217 * @dest_dentry: destination dentry. 218 * @source_mnt: source mount. 219 * @tree_list : list of heads of trees to be attached. 220 */ 221 int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry, 222 struct mount *source_mnt, struct list_head *tree_list) 223 { 224 struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns; 225 struct mount *m, *child; 226 int ret = 0; 227 struct mount *prev_dest_mnt = dest_mnt; 228 struct mount *prev_src_mnt = source_mnt; 229 LIST_HEAD(tmp_list); 230 LIST_HEAD(umount_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_dentry, m->mnt.mnt_root)) { 254 mnt_set_mountpoint(m, dest_dentry, 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, &umount_list); 271 } 272 br_write_unlock(&vfsmount_lock); 273 release_mounts(&umount_list); 274 return ret; 275 } 276 277 /* 278 * return true if the refcount is greater than count 279 */ 280 static inline int do_refcount_check(struct mount *mnt, int count) 281 { 282 int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts; 283 return (mycount > count); 284 } 285 286 /* 287 * check if the mount 'mnt' can be unmounted successfully. 288 * @mnt: the mount to be checked for unmount 289 * NOTE: unmounting 'mnt' would naturally propagate to all 290 * other mounts its parent propagates to. 291 * Check if any of these mounts that **do not have submounts** 292 * have more references than 'refcnt'. If so return busy. 293 * 294 * vfsmount lock must be held for write 295 */ 296 int propagate_mount_busy(struct mount *mnt, int refcnt) 297 { 298 struct mount *m, *child; 299 struct mount *parent = mnt->mnt_parent; 300 int ret = 0; 301 302 if (mnt == parent) 303 return do_refcount_check(mnt, refcnt); 304 305 /* 306 * quickly check if the current mount can be unmounted. 307 * If not, we don't have to go checking for all other 308 * mounts 309 */ 310 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt)) 311 return 1; 312 313 for (m = propagation_next(parent, parent); m; 314 m = propagation_next(m, parent)) { 315 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint, 0); 316 if (child && list_empty(&child->mnt_mounts) && 317 (ret = do_refcount_check(child, 1))) 318 break; 319 } 320 return ret; 321 } 322 323 /* 324 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its 325 * parent propagates to. 326 */ 327 static void __propagate_umount(struct mount *mnt) 328 { 329 struct mount *parent = mnt->mnt_parent; 330 struct mount *m; 331 332 BUG_ON(parent == mnt); 333 334 for (m = propagation_next(parent, parent); m; 335 m = propagation_next(m, parent)) { 336 337 struct mount *child = __lookup_mnt(&m->mnt, 338 mnt->mnt_mountpoint, 0); 339 /* 340 * umount the child only if the child has no 341 * other children 342 */ 343 if (child && list_empty(&child->mnt_mounts)) 344 list_move_tail(&child->mnt_hash, &mnt->mnt_hash); 345 } 346 } 347 348 /* 349 * collect all mounts that receive propagation from the mount in @list, 350 * and return these additional mounts in the same list. 351 * @list: the list of mounts to be unmounted. 352 * 353 * vfsmount lock must be held for write 354 */ 355 int propagate_umount(struct list_head *list) 356 { 357 struct mount *mnt; 358 359 list_for_each_entry(mnt, list, mnt_hash) 360 __propagate_umount(mnt); 361 return 0; 362 } 363