Commit 813d32f9 authored Oct 14, 2014 by Darrick J. Wong Committed by Theodore Ts'o Oct 14, 2014

ext4: check s_chksum_driver when looking for bg csum presence



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>
Cc: stable@vger.kernel.org

parent aef4885a

fs/ext4/ext4.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -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)

fs/ext4/super.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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));

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