Re: [PATCH v2] btrfs: ensure that a DUP or RAID1 block group has exactly two stripes

[Hans van Kranenburg <Hans.van.Kranenburg@mendix.com>]

On 2/18/19 10:48 AM, Johannes Thumshirn wrote:
> We recently had a customer issue with a corrupted filesystem. When trying
> to mount this image btrfs panicked with a division by zero in
> calc_stripe_length().
> 
> The corrupt chunk had a 'num_stripes' value of 1. calc_stripe_length()
> takes this value and divides it by the number of copies the RAID profile is
> expected to have to calculate the amount of data stripes. As a DUP profile
> is expected to have 2 copies this division resulted in 1/2 = 0. Later then
> the 'data_stripes' variable is used as a divisor in the stripe length
> calculation which results in a division by 0 and thus a kernel panic.
> 
> When encountering a filesystem with a DUP block group and a 'num_stripes'
> value unequal to 2, refuse mounting as the image is corrupted and will lead
> to unexpected behaviour.
> 
> Code inspection showed a RAID1 block group has the same issues.
> 
> Fixes: e06cd3dd7cea ("Btrfs: add validadtion checks for chunk loading")
> Cc: Liu Bo <obuil.liubo@gmail.com>
> Reviewed-by: Qu Wenruo <wqu@suse.com>
> Reviewed-by: Nikolay Borisov <nborisov@suse.com>
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
> Changes to v1:
> - Also add the check for RAID1 (Hans)
> ---
>  fs/btrfs/volumes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 03f223aa7194..a4d12ada0565 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6791,10 +6791,10 @@ static int btrfs_check_chunk_valid(struct btrfs_fs_info *fs_info,
>  	}
>  
>  	if ((type & BTRFS_BLOCK_GROUP_RAID10 && sub_stripes != 2) ||
> -	    (type & BTRFS_BLOCK_GROUP_RAID1 && num_stripes < 1) ||
> +	    (type & BTRFS_BLOCK_GROUP_RAID1 && num_stripes != 1) ||

I think you meant != 2 here. It's just like DUP, but with the two of
them on different devices instead of the same.

>  	    (type & BTRFS_BLOCK_GROUP_RAID5 && num_stripes < 2) ||
>  	    (type & BTRFS_BLOCK_GROUP_RAID6 && num_stripes < 3) ||
> -	    (type & BTRFS_BLOCK_GROUP_DUP && num_stripes > 2) ||
> +	    (type & BTRFS_BLOCK_GROUP_DUP && num_stripes != 2) ||
>  	    ((type & BTRFS_BLOCK_GROUP_PROFILE_MASK) == 0 &&
>  	     num_stripes != 1)) {
>  		btrfs_err(fs_info,
> 

Thanks,

-- 
Hans van Kranenburg