check-s_chksum_driver-when-looking-for-bg-csum-presence

   1 ext4: check s_chksum_driver when looking for bg csum presence
   2
   3 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   4
   5 Convert the ext4_has_group_desc_csum predicate to look for a checksum
   6 driver instead of the metadata_csum flag and change the bg checksum
   7 calculation function to look for GDT_CSUM before taking the crc16
   8 path.
   9
  10 Without this patch, if we mount with ^uninit_bg,^metadata_csum and
  11 later metadata_csum gets turned on by accident, the block group
  12 checksum functions will incorrectly assume that checksumming is
  13 enabled (metadata_csum) but that crc16 should be used
  14 (!s_chksum_driver).  This is totally wrong, so fix the predicate
  15 and the checksum formula selection.
  16
  17 (Granted, if the metadata_csum feature bit gets enabled on a live FS
  18 then something underhanded is going on, but we could at least avoid
  19 writing garbage into the on-disk fields.)
  20
  21 Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  22 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  23 Reviewed-by: Dmitry Monakhov <dmonakhov@openvz.org>
  24 Cc: stable@vger.kernel.org
  25 ---
  26  fs/ext4/ext4.h  |    4 ++--
  27  fs/ext4/super.c |    4 ++++
  28  2 files changed, 6 insertions(+), 2 deletions(-)
  29
  30 diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
  31 index fb6aadf..db38ca0f 100644
  32 --- a/fs/ext4/ext4.h
  33 +++ b/fs/ext4/ext4.h
  34 @@ -2367,8 +2367,8 @@ extern int ext4_register_li_request(struct super_block *sb,
  35  static inline int ext4_has_group_desc_csum(struct super_block *sb)
  36  {
  37         return EXT4_HAS_RO_COMPAT_FEATURE(sb,
  38 -                                         EXT4_FEATURE_RO_COMPAT_GDT_CSUM |
  39 -                                         EXT4_FEATURE_RO_COMPAT_METADATA_CSUM);
  40 +                                         EXT4_FEATURE_RO_COMPAT_GDT_CSUM) ||
  41 +              (EXT4_SB(sb)->s_chksum_driver != NULL);
  42  }
  43
  44  static inline int ext4_has_metadata_csum(struct super_block *sb)
  45 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  46 index 6ae47d4..de38a96 100644
  47 --- a/fs/ext4/super.c
  48 +++ b/fs/ext4/super.c
  49 @@ -2032,6 +2032,10 @@ static __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,
  50         }
  51
  52         /* old crc16 code */
  53 +       if (!(sbi->s_es->s_feature_ro_compat &
  54 +             cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)))
  55 +               return 0;
  56 +
  57         offset = offsetof(struct ext4_group_desc, bg_checksum);
  58
  59         crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));
  60