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

[Johannes Thumshirn <jthumshirn@suse.de>]

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) ||
 	    (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,
-- 
2.16.4