Re: [PATCH 2/5] btrfs: tree-checker: Detect invalid empty essential tree

[Nikolay Borisov <nborisov@suse.com>]

On  3.07.2018 12:10, Qu Wenruo wrote:
> A crafted image has empty root tree block, which will cause later NULL
> pointer dereference.
> 
> The following trees should never be empty:
> 1) Tree root
>    Must contain at least root items for extent tree, device tree and fs
>    tree
> 
> 2) Chunk tree
>    Or we can't even bootstrap.
> 
> 3) Fs tree
>    At least inode item for top level inode (.).
> 
> 4) Device tree
>    Dev extents for chunks
> 
> 5) Extent tree
>    Must has corresponding extent for each chunk.
> 
> If any is empty, we are sure the fs is corrupted and no need to mount
> it.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=199847
> Reported-by: Xu Wen <wen.xu@gatech.edu>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/tree-checker.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index 1cd735b099df..3a307efab46b 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -497,8 +497,20 @@ static int check_leaf(struct btrfs_fs_info *fs_info, struct extent_buffer *leaf,
>  	 * skip this check for relocation trees.
>  	 */
>  	if (nritems == 0 && !btrfs_header_flag(leaf, BTRFS_HEADER_FLAG_RELOC)) {
> +		u64 owner = btrfs_header_owner(leaf);

nit: Since you assign the owner of the leaf to a variable use this
variable when initialising key object below.

>  		struct btrfs_root *check_root;
>  
> +		/* These trees should never be empty */
> +		if (owner == BTRFS_ROOT_TREE_OBJECTID ||
> +		    owner == BTRFS_CHUNK_TREE_OBJECTID ||
> +		    owner == BTRFS_EXTENT_TREE_OBJECTID ||
> +		    owner == BTRFS_DEV_TREE_OBJECTID ||
> +		    owner == BTRFS_FS_TREE_OBJECTID) {
> +			generic_err(fs_info, leaf, 0,
> +			"invalid root, root %llu should never be empty",
> +				    owner);
> +			return -EUCLEAN;
> +		}
>  		key.objectid = btrfs_header_owner(leaf);
>  		key.type = BTRFS_ROOT_ITEM_KEY;
>  		key.offset = (u64)-1;
>