Re: [PATCH] Btrfs: fix NULL pointer dereference in log_dir_items

[Nikolay Borisov <nborisov@suse.com>]

On 31.03.2018 01:11, Liu Bo wrote:
> 0, 1 and <0 can be returned by btrfs_next_leaf(), and when <0 is
> returned, path->nodes[0] could be NULL, log_dir_items lacks such a
> check for <0 and we may run into a null pointer dereference panic.
> 
> Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>

This bug has been present ever since 2.6.29 (e02119d5a7b4 ("Btrfs: Add a
write ahead tree log to optimize synchronous operations"))
 so this needs a stable tag.

> ---
>  fs/btrfs/tree-log.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 4344577..4ee9431 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -3518,8 +3518,11 @@ static noinline int log_dir_items(struct btrfs_trans_handle *trans,
>  		 * from this directory and from this transaction
>  		 */
>  		ret = btrfs_next_leaf(root, path);
> -		if (ret == 1) {
> -			last_offset = (u64)-1;
> +		if (ret) {
> +			if (ret == 1)
> +				last_offset = (u64)-1;
> +			else
> +				err = ret;
>  			goto done;
>  		}
>  		btrfs_item_key_to_cpu(path->nodes[0], &tmp, path->slots[0]);
>