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

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

On 2/13/19 3:26 PM, 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.
> 
> Fixes: e06cd3dd7cea ("Btrfs: add validadtion checks for chunk loading")
> Cc: Liu Bo <obuil.liubo@gmail.com>
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>  fs/btrfs/volumes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 03f223aa7194..b40cc7c830f4 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6794,7 +6794,7 @@ static int btrfs_check_chunk_valid(struct btrfs_fs_info *fs_info,
>  	    (type & BTRFS_BLOCK_GROUP_RAID1 && num_stripes < 1) ||
>  	    (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,
> 

It looks like the RAID1 check has a similar problem. Shouldn't that
check also be != 2 ?

Hans