linux-kernel - [PATCH 5.5 084/189] btrfs: fix RAID direct I/O reads with alternate csums

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Date:   Tue, 10 Mar 2020 13:38:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Omar Sandoval <osandov@...com>, David Sterba <dsterba@...e.com>
Subject: [PATCH 5.5 084/189] btrfs: fix RAID direct I/O reads with alternate csums

From: Omar Sandoval <osandov@...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@...r.kernel.org # 5.4+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@....com>
Signed-off-by: Omar Sandoval <osandov@...com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8444,6 +8444,7 @@ 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;
 
 	/*
@@ -8463,7 +8464,8 @@ 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;
 }