On 18/02/2019 10:55, Hans van Kranenburg wrote:
> 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@xxxxxxxxx>
>> Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
>> Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
>> Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
>> ---
>> 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.
Ah damn, thanks.
--
Johannes Thumshirn SUSE Labs Filesystems
jthumshirn@xxxxxxx +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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