From 76a66ba101329316a5d7f4275070be22eb85fdf2 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Fri, 21 Oct 2022 08:43:45 +0800 Subject: [PATCH] btrfs: don't use btrfs_chunk::sub_stripes from disk [BUG] There are two reports (the earliest one from LKP, a more recent one from kernel bugzilla) that we can have some chunks with 0 as sub_stripes. This will cause divide-by-zero errors at btrfs_rmap_block, which is introduced by a recent kernel patch ac0677348f3c ("btrfs: merge calculations for simple striped profiles in btrfs_rmap_block"): if (map->type & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) { stripe_nr = stripe_nr * map->num_stripes + i; stripe_nr = div_u64(stripe_nr, map->sub_stripes); <<< } [CAUSE] From the more recent report, it has been proven that we have some chunks with 0 as sub_stripes, mostly caused by older mkfs. It turns out that the mkfs.btrfs fix is only introduced in 6718ab4d33aa ("btrfs-progs: Initialize sub_stripes to 1 in btrfs_alloc_data_chunk") which is included in v5.4 btrfs-progs release. So there would be quite some old filesystems with such 0 sub_stripes. [FIX] Just don't trust the sub_stripes values from disk. We have a trusted btrfs_raid_array[] to fetch the correct sub_stripes numbers for each profile and that are fixed. By this, we can keep the compatibility with older filesystems while still avoid divide-by-zero bugs. Reported-by: kernel test robot Reported-by: Viktor Kuzmin Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216559 Fixes: ac0677348f3c ("btrfs: merge calculations for simple striped profiles in btrfs_rmap_block") CC: stable@vger.kernel.org # 6.0 Reviewed-by: Su Yue Reviewed-by: Johannes Thumshirn Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 94ba46d..a8d4bc6 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -7142,6 +7142,7 @@ static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf, u64 devid; u64 type; u8 uuid[BTRFS_UUID_SIZE]; + int index; int num_stripes; int ret; int i; @@ -7149,6 +7150,7 @@ static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf, logical = key->offset; length = btrfs_chunk_length(leaf, chunk); type = btrfs_chunk_type(leaf, chunk); + index = btrfs_bg_flags_to_raid_index(type); num_stripes = btrfs_chunk_num_stripes(leaf, chunk); #if BITS_PER_LONG == 32 @@ -7202,7 +7204,15 @@ static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf, map->io_align = btrfs_chunk_io_align(leaf, chunk); map->stripe_len = btrfs_chunk_stripe_len(leaf, chunk); map->type = type; - map->sub_stripes = btrfs_chunk_sub_stripes(leaf, chunk); + /* + * We can't use the sub_stripes value, as for profiles other than + * RAID10, they may have 0 as sub_stripes for filesystems created by + * older mkfs (sub_stripes = btrfs_raid_array[index].sub_stripes; map->verified_stripes = 0; em->orig_block_len = btrfs_calc_stripe_length(em); for (i = 0; i < num_stripes; i++) { -- 2.7.4