btrfs: ensure that a DUP or RAID1 block group has exactly two stripes

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: stable@vger.kernel.org # 4.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 03f223aa7194daa0da05c9cab5a357f38927cef1..9024eee889b9838caa2799ca51f439106a955ff0 100644 (file)
--- 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 != 2) ||
            (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,