mirror of https://gitee.com/openkylin/linux.git
teach move_mount(2) to work with OPEN_TREE_CLONE
Allow a detached tree created by open_tree(..., OPEN_TREE_CLONE) to be attached by move_mount(2). If by the time of final fput() of OPEN_TREE_CLONE-opened file its tree is not detached anymore, it won't be dissolved. move_mount(2) is adjusted to handle detached source. That gives us equivalents of mount --bind and mount --rbind. Thanks also to Alan Jenkins <alan.christopher.jenkins@gmail.com> for providing a whole bunch of ways to break things using this interface. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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2db154b3ea
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@ -1842,10 +1842,16 @@ void dissolve_on_fput(struct vfsmount *mnt)
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namespace_lock();
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lock_mount_hash();
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ns = real_mount(mnt)->mnt_ns;
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umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
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if (ns) {
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if (is_anon_ns(ns))
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umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
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else
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ns = NULL;
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}
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unlock_mount_hash();
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namespace_unlock();
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free_mnt_ns(ns);
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if (ns)
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free_mnt_ns(ns);
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}
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void drop_collected_mounts(struct vfsmount *mnt)
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@ -2081,6 +2087,10 @@ static int attach_recursive_mnt(struct mount *source_mnt,
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attach_mnt(source_mnt, dest_mnt, dest_mp);
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touch_mnt_namespace(source_mnt->mnt_ns);
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} else {
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if (source_mnt->mnt_ns) {
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/* move from anon - the caller will destroy */
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list_del_init(&source_mnt->mnt_ns->list);
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}
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mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
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commit_tree(source_mnt);
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}
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@ -2539,13 +2549,37 @@ static inline int tree_contains_unbindable(struct mount *mnt)
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return 0;
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}
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/*
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* Check that there aren't references to earlier/same mount namespaces in the
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* specified subtree. Such references can act as pins for mount namespaces
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* that aren't checked by the mount-cycle checking code, thereby allowing
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* cycles to be made.
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*/
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static bool check_for_nsfs_mounts(struct mount *subtree)
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{
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struct mount *p;
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bool ret = false;
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lock_mount_hash();
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for (p = subtree; p; p = next_mnt(p, subtree))
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if (mnt_ns_loop(p->mnt.mnt_root))
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goto out;
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ret = true;
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out:
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unlock_mount_hash();
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return ret;
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}
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static int do_move_mount(struct path *old_path, struct path *new_path)
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{
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struct path parent_path = {.mnt = NULL, .dentry = NULL};
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struct mnt_namespace *ns;
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struct mount *p;
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struct mount *old;
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struct mountpoint *mp;
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int err;
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bool attached;
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mp = lock_mount(new_path);
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if (IS_ERR(mp))
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@ -2553,12 +2587,19 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
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old = real_mount(old_path->mnt);
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p = real_mount(new_path->mnt);
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attached = mnt_has_parent(old);
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ns = old->mnt_ns;
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err = -EINVAL;
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if (!check_mnt(p) || !check_mnt(old))
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/* The mountpoint must be in our namespace. */
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if (!check_mnt(p))
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goto out;
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if (!mnt_has_parent(old))
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/* The thing moved should be either ours or completely unattached. */
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if (attached && !check_mnt(old))
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goto out;
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if (!attached && !is_anon_ns(ns))
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goto out;
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if (old->mnt.mnt_flags & MNT_LOCKED)
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@ -2573,7 +2614,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
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/*
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* Don't move a mount residing in a shared parent.
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*/
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if (IS_MNT_SHARED(old->mnt_parent))
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if (attached && IS_MNT_SHARED(old->mnt_parent))
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goto out;
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/*
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* Don't move a mount tree containing unbindable mounts to a destination
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@ -2582,12 +2623,14 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
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if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
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goto out;
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err = -ELOOP;
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if (!check_for_nsfs_mounts(old))
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goto out;
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for (; mnt_has_parent(p); p = p->mnt_parent)
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if (p == old)
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goto out;
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err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,
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&parent_path);
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attached ? &parent_path : NULL);
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if (err)
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goto out;
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@ -2596,8 +2639,11 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
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list_del_init(&old->mnt_expire);
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out:
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unlock_mount(mp);
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if (!err)
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if (!err) {
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path_put(&parent_path);
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if (!attached)
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free_mnt_ns(ns);
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}
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return err;
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}
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@ -3289,6 +3335,8 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
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/*
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* Move a mount from one place to another.
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* In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be
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* used to copy a mount subtree.
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*
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* Note the flags value is a combination of MOVE_MOUNT_* flags.
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*/
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