[PATCH 5.4 079/168] btrfs: fix RAID direct I/O reads with alternate csums

Greg Kroah-Hartman
2020-03-10T13:29:58Z

From: Omar Sandoval <osandov@fb.com>

commit e7a04894c766daa4248cb736efee93550f2d5872 upstream.

btrfs_lookup_and_bind_dio_csum() does pointer arithmetic which assumes
32-bit checksums. If using a larger checksum, this leads to spurious
failures when a direct I/O read crosses a stripe. This is easy
to reproduce:

# mkfs.btrfs -f --checksum blake2 -d raid0 /dev/vdc /dev/vdd
...
# mount /dev/vdc /mnt
# cd /mnt
# dd if=/dev/urandom of=foo bs=1M count=1 status=none
# dd if=foo of=/dev/null bs=1M iflag=direct status=none
dd: error reading 'foo': Input/output error
# dmesg | tail -1
[ 135.821568] BTRFS warning (device vdc): csum failed root 5 ino 257 off 421888 ...

Fix it by using the actual checksum size.

Fixes: 1e25a2e3ca0d ("btrfs: don't assume ordered sums to be 4 bytes")
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/inode.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8426,6 +8426,7 @@ static inline blk_status_t btrfs_lookup_
{
struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
struct btrfs_io_bio *orig_io_bio = btrfs_io_bio(dip->orig_bio);
+ u16 csum_size;
blk_status_t ret;

/*
@@ -8445,7 +8446,8 @@ static inline blk_status_t btrfs_lookup_

file_offset -= dip->logical_offset;
file_offset >>= inode->i_sb->s_blocksize_bits;
- io_bio->csum = (u8 *)(((u32 *)orig_io_bio->csum) + file_offset);
+ csum_size = btrfs_super_csum_size(btrfs_sb(inode->i_sb)->super_copy);
+ io_bio->csum = orig_io_bio->csum + csum_size * file_offset;

return 0;
}