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Commit ea9e8b11 authored by Chris Mason's avatar Chris Mason
Browse files

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: default avatarChris Mason <chris.mason@oracle.com>
parent 0660b5af

fs/btrfs/ctree.h

+3 −0
Original line number Diff line number Diff line
@@ -1801,6 +1801,9 @@ int btrfs_drop_subtree(struct btrfs_trans_handle *trans, 
			struct extent_buffer *node,

			struct extent_buffer *parent);

/* root-item.c */

int btrfs_find_root_ref(struct btrfs_root *tree_root,

		   struct btrfs_path *path,

		   u64 root_id, u64 ref_id);

int btrfs_add_root_ref(struct btrfs_trans_handle *trans,

		       struct btrfs_root *tree_root,

		       u64 root_id, u8 type, u64 ref_id,

fs/btrfs/disk-io.c

+4 −1
Original line number Diff line number Diff line
@@ -1129,7 +1129,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info, 
		kfree(root);

		return ERR_PTR(ret);

	}



#if 0

	ret = btrfs_sysfs_add_root(root);

	if (ret) {

		free_extent_buffer(root->node);
@@ -1137,6 +1137,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info, 
		kfree(root);

		return ERR_PTR(ret);

	}

#endif

	root->in_sysfs = 1;

	return root;

}
@@ -1963,8 +1964,10 @@ int btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root) 
		down_write(&root->anon_super.s_umount);

		kill_anon_super(&root->anon_super);

	}

#if 0

	if (root->in_sysfs)

		btrfs_sysfs_del_root(root);

#endif

	if (root->node)

		free_extent_buffer(root->node);

	if (root->commit_root)

fs/btrfs/ioctl.c

+50 −0
Original line number Diff line number Diff line
@@ -284,6 +284,56 @@ static noinline int btrfs_mksubvol(struct path *parent, char *name, 
	 * 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,

fs/btrfs/root-tree.c

+16 −0
Original line number Diff line number Diff line
@@ -300,6 +300,22 @@ int btrfs_del_root_ref(struct btrfs_trans_handle *trans, 
	return ret;

}



int btrfs_find_root_ref(struct btrfs_root *tree_root,

		   struct btrfs_path *path,

		   u64 root_id, u64 ref_id)

{

	struct btrfs_key key;

	int ret;



	key.objectid = root_id;

	key.type = BTRFS_ROOT_REF_KEY;

	key.offset = ref_id;



	ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);

	return ret;

}





/*

 * add a btrfs_root_ref item.  type is either BTRFS_ROOT_REF_KEY

 * or BTRFS_ROOT_BACKREF_KEY.