ext4: check s_chksum_driver when looking for bg csum presence

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>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index f57e9a795c5f3a6cfa5858a8066307c53cfa1442..2a6830a7af33df1b119780537cb44e8d514a4c50 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2341,8 +2341,8 @@ extern int ext4_register_li_request(struct super_block *sb,
 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)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6686ce4a87738bb8cb653f21e15552c32ab2d807..608db5820740b6364fa0c07d288abe62d41def64 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2019,6 +2019,10 @@ static __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,
        }
 
        /* 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));