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 (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 */
 119void 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 */
 146static 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 */
 176static 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 */
 222int 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        }
 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);
 271        }
 272        br_write_unlock(&vfsmount_lock);
 273        return ret;
 274}
 275
 276/*
 277 * return true if the refcount is greater than count
 278 */
 279static 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 */
 295int 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 */
 326static 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 */
 354int 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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