[3.16.y-ckt extended stable] Patch "ext4: check s_chksum_driver when looking for bg csum presence" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ext4: check s_chksum_driver when looking for bg csum presence

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c6243bdb2f0a6a1767e52a6d127f4441ba6b8503 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong at oracle.com>
Date: Tue, 14 Oct 2014 02:35:49 -0400
Subject: 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 at oracle.com>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Reviewed-by: Dmitry Monakhov <dmonakhov at openvz.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 cf79b1d9b028..20889da7f8a0 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2332,8 +2332,8 @@ 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 872f5a188a0d..a6c188bb5265 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2025,6 +2025,10 @@ 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));
--
2.1.0