Btrfs: prevent loops in the directory tree when creating snapshots
For a directory tree:
/mnt/subvolA/subvolB
btrfsctl -s /mnt/subvolA/subvolB /mnt
Will create a directory loop with subvolA under subvolB. This
commit uses the forward refs for each subvol and snapshot to error out
before creating the loop.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 536ae88..8828109 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -284,6 +284,56 @@
* subvolume with specific mode bits.
*/
if (snap_src) {
+ struct dentry *dir = dentry->d_parent;
+ struct dentry *test = dir->d_parent;
+ struct btrfs_path *path = btrfs_alloc_path();
+ int ret;
+ u64 test_oid;
+ u64 parent_oid = BTRFS_I(dir->d_inode)->root->root_key.objectid;
+
+ test_oid = snap_src->root_key.objectid;
+
+ ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
+ path, parent_oid, test_oid);
+ if (ret == 0)
+ goto create;
+ btrfs_release_path(snap_src->fs_info->tree_root, path);
+
+ /* we need to make sure we aren't creating a directory loop
+ * by taking a snapshot of something that has our current
+ * subvol in its directory tree. So, this loops through
+ * the dentries and checks the forward refs for each subvolume
+ * to see if is references the subvolume where we are
+ * placing this new snapshot.
+ */
+ while(1) {
+ if (!test ||
+ dir == snap_src->fs_info->sb->s_root ||
+ test == snap_src->fs_info->sb->s_root ||
+ test->d_inode->i_sb != snap_src->fs_info->sb) {
+ break;
+ }
+ if (S_ISLNK(test->d_inode->i_mode)) {
+ printk("Symlink in snapshot path, failed\n");
+ error = -EMLINK;
+ btrfs_free_path(path);
+ goto out_drop_write;
+ }
+ test_oid =
+ BTRFS_I(test->d_inode)->root->root_key.objectid;
+ ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
+ path, test_oid, parent_oid);
+ if (ret == 0) {
+ printk("Snapshot creation failed, looping\n");
+ error = -EMLINK;
+ btrfs_free_path(path);
+ goto out_drop_write;
+ }
+ btrfs_release_path(snap_src->fs_info->tree_root, path);
+ test = test->d_parent;
+ }
+create:
+ btrfs_free_path(path);
error = create_snapshot(snap_src, dentry, name, namelen);
} else {
error = create_subvol(BTRFS_I(parent->dentry->d_inode)->root,