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    Subject[PATCH 3.17 160/319] ext4: check s_chksum_driver when looking for bg csum presence
    Date
    3.17-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Darrick J. Wong" <darrick.wong@oracle.com>

    commit 813d32f91333e4c33d5a19b67167c4bae42dae75 upstream.

    Convert the ext4_has_group_desc_csum predicate to look for a checksum
    driver instead of the metadata_csum flag and change the bg checksum
    calculation function to look for GDT_CSUM before taking the crc16
    path.

    Without this patch, if we mount with ^uninit_bg,^metadata_csum and
    later metadata_csum gets turned on by accident, the block group
    checksum functions will incorrectly assume that checksumming is
    enabled (metadata_csum) but that crc16 should be used
    (!s_chksum_driver). This is totally wrong, so fix the predicate
    and the checksum formula selection.

    (Granted, if the metadata_csum feature bit gets enabled on a live FS
    then something underhanded is going on, but we could at least avoid
    writing garbage into the on-disk fields.)

    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Reviewed-by: Dmitry Monakhov <dmonakhov@openvz.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/ext4.h | 4 ++--
    fs/ext4/super.c | 4 ++++
    2 files changed, 6 insertions(+), 2 deletions(-)

    --- a/fs/ext4/ext4.h
    +++ b/fs/ext4/ext4.h
    @@ -2333,8 +2333,8 @@ extern int ext4_register_li_request(stru
    static inline int ext4_has_group_desc_csum(struct super_block *sb)
    {
    return EXT4_HAS_RO_COMPAT_FEATURE(sb,
    - EXT4_FEATURE_RO_COMPAT_GDT_CSUM |
    - EXT4_FEATURE_RO_COMPAT_METADATA_CSUM);
    + EXT4_FEATURE_RO_COMPAT_GDT_CSUM) ||
    + (EXT4_SB(sb)->s_chksum_driver != NULL);
    }

    static inline int ext4_has_metadata_csum(struct super_block *sb)
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -2025,6 +2025,10 @@ static __le16 ext4_group_desc_csum(struc
    }

    /* old crc16 code */
    + if (!(sbi->s_es->s_feature_ro_compat &
    + cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)))
    + return 0;
    +
    offset = offsetof(struct ext4_group_desc, bg_checksum);

    crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));



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