[PATCH] xfs: growfs overruns AGFL buffer on V4 filesystems

[Dave Chinner]

From: Dave Chinner <dchinner at redhat.com>

This loop in xfs_growfs_data_private() is incorrect for V4
superblocks filesystems:

		for (bucket = 0; bucket < XFS_AGFL_SIZE(mp); bucket++)
			agfl->agfl_bno[bucket] = cpu_to_be32(NULLAGBLOCK);

For V4 filesystems, we don't have a agfl header structure, and so
XFS_AGFL_SIZE() returns an entire sector's worth of entries, which
we then index from an offset into the sector. Hence: buffer overrun.

This problem was introduced in 3.10 by commit 77c95bba ("xfs: add
CRC checks to the AGFL") which changed the AGFL structure but failed
to update the growfs code to handle the different structures.

Fix it by using the correct offset into the buffer for both V4 and
V5 filesystems.

Cc: <stable at vger.kernel.org>
Signed-off-by: Dave Chinner <dchinner at redhat.com>
---
 fs/xfs/xfs_fsops.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index a6e54b3..02fb943 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -220,6 +220,8 @@ xfs_growfs_data_private(
 	 */
 	nfree = 0;
 	for (agno = nagcount - 1; agno >= oagcount; agno--, new -= agsize) {
+		__be32	*agfl_bno;
+
 		/*
 		 * AG freespace header block
 		 */
@@ -279,8 +281,10 @@ xfs_growfs_data_private(
 			agfl->agfl_seqno = cpu_to_be32(agno);
 			uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_uuid);
 		}
+
+		agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, bp);
 		for (bucket = 0; bucket < XFS_AGFL_SIZE(mp); bucket++)
-			agfl->agfl_bno[bucket] = cpu_to_be32(NULLAGBLOCK);
+			agfl_bno[bucket] = cpu_to_be32(NULLAGBLOCK);
 
 		error = xfs_bwrite(bp);
 		xfs_buf_relse(bp);
-- 
1.8.4.rc3