linux-kernel - [PATCH 3.12 141/142] libxfs: pack the agfl header structure so XFS_AGFL

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Date:	Wed, 24 Feb 2016 11:05:36 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Dave Chinner <david@...morbit.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 141/142] libxfs: pack the agfl header structure so XFS_AGFL_SIZE is correct

From: "Darrick J. Wong" <darrick.wong@...cle.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 96f859d52bcb1c6ea6f3388d39862bf7143e2f30 upstream.

Because struct xfs_agfl is 36 bytes long and has a 64-bit integer
inside it, gcc will quietly round the structure size up to the nearest
64 bits -- in this case, 40 bytes.  This results in the XFS_AGFL_SIZE
macro returning incorrect results for v5 filesystems on 64-bit
machines (118 items instead of 119).  As a result, a 32-bit xfs_repair
will see garbage in AGFL item 119 and complain.

Therefore, tell gcc not to pad the structure so that the AGFL size
calculation is correct.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Reviewed-by: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/xfs/xfs_ag.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 1cb740afd674..78ec58fc282e 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -224,7 +224,7 @@ typedef struct xfs_agfl {
 	__be64		agfl_lsn;
 	__be32		agfl_crc;
 	__be32		agfl_bno[];	/* actually XFS_AGFL_SIZE(mp) */
-} xfs_agfl_t;
+} __attribute__((packed)) xfs_agfl_t;

 /*
  * tags for inode radix tree
-- 
2.7.1