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Subject[PATCH 3.13 074/162] ext4: check s_chksum_driver when looking for bg csum presence
Date -stable review patch.  If anyone has any objections, please let me know.


From: "Darrick J. Wong" <>

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

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 <>
Signed-off-by: Theodore Ts'o <>
Reviewed-by: Dmitry Monakhov <>
Signed-off-by: Kamal Mostafa <>
fs/ext4/ext4.h | 4 ++--
fs/ext4/super.c | 4 ++++
2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5b250fe..bfb7fed 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2337,8 +2337,8 @@ extern int ext4_register_li_request(struct super_block *sb,
static inline int ext4_has_group_desc_csum(struct super_block *sb)
+ (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 6686ce4..608db58 100644
--- 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 &
+ 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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