ext4: check s_chksum_driver when looking for bg csum presence

djwong · tytso · commit 813d32f91333 · 2014-10-14T02:35:49.000-04:00
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 &lt;darrick.wong@oracle.com&gt;
Signed-off-by: Theodore Ts'o &lt;tytso@mit.edu&gt;
Reviewed-by: Dmitry Monakhov &lt;dmonakhov@openvz.org&gt;
Cc: stable@vger.kernel.org
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
@@ -2333,8 +2333,8 @@ 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
@@ -2005,6 +2005,10 @@ 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));

Original file line number	Diff line number	Diff line change
`@@ -2333,8 +2333,8 @@ extern int ext4_register_li_request(struct super_block *sb,`
`2333`	`2333`	`static inline int ext4_has_group_desc_csum(struct super_block *sb)`
`2334`	`2334`	`{`
`2335`	`2335`	`return EXT4_HAS_RO_COMPAT_FEATURE(sb,`
`2336`		`- EXT4_FEATURE_RO_COMPAT_GDT_CSUM \|`
`2337`		`- EXT4_FEATURE_RO_COMPAT_METADATA_CSUM);`
	`2336`	`+ EXT4_FEATURE_RO_COMPAT_GDT_CSUM) \|\|`
	`2337`	`+ (EXT4_SB(sb)->s_chksum_driver != NULL);`
`2338`	`2338`	`}`
`2339`	`2339`
`2340`	`2340`	`static inline int ext4_has_metadata_csum(struct super_block *sb)`
Original file line number	Diff line number	Diff line change
`@@ -2005,6 +2005,10 @@ static __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,`
`2005`	`2005`	`}`
`2006`	`2006`
`2007`	`2007`	`/* old crc16 code */`
	`2008`	`+ if (!(sbi->s_es->s_feature_ro_compat &`
	`2009`	`+ cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)))`
	`2010`	`+ return 0;`
	`2011`	`+`
`2008`	`2012`	`offset = offsetof(struct ext4_group_desc, bg_checksum);`
`2009`	`2013`
`2010`	`2014`	`crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));`