linux/fs/pnode.c
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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 */
  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 *next_slave(struct mount *p)
  28{
  29        return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
  30}
  31
  32static 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 */
  55int 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
  68static 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 */
 118void 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 */
 145static 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 */
 175static 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 */
 221int 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        }
 266out:
 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 */
 280static 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 */
 296int 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 */
 327static 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 */
 355int 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