[PATCH 4.2.y-ckt 079/268] libxfs: pack the agfl header structure so XFS_AGFL_SIZE is correct

From: Kamal Mostafa
Date: Wed Jan 27 2016 - 16:44:42 EST

4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know.


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

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@xxxxxxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
fs/xfs/libxfs/xfs_format.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index a0ae572..cfb8dd6 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -762,7 +762,7 @@ 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;

#define XFS_AGFL_CRC_OFF offsetof(struct xfs_agfl, agfl_crc)