[SRU][X/A/B][PATCH 1/1] xfs: set format back to extents if xfs_bmap_extents_to_btree

[Khalid Elmously]

From: Eric Sandeen <sandeen at redhat.com>

CVE-2018-10323

If xfs_bmap_extents_to_btree fails in a mode where we call
xfs_iroot_realloc(-1) to de-allocate the root, set the
format back to extents.

Otherwise we can assume we can dereference ifp->if_broot
based on the XFS_DINODE_FMT_BTREE format, and crash.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199423
Signed-off-by: Eric Sandeen <sandeen at redhat.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong at oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
(cherry-picked from 2c4306f719b083d17df2963bc761777576b8ad1b)
Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
---
 fs/xfs/libxfs/xfs_bmap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 1bddbba6b80c..c756db755a5a 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -725,12 +725,16 @@ xfs_bmap_extents_to_btree(
 	*logflagsp = 0;
 	if ((error = xfs_alloc_vextent(&args))) {
 		xfs_iroot_realloc(ip, -1, whichfork);
+		ASSERT(ifp->if_broot == NULL);
+		XFS_IFORK_FMT_SET(ip, whichfork, XFS_DINODE_FMT_EXTENTS);
 		xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
 		return error;
 	}
 
 	if (WARN_ON_ONCE(args.fsbno == NULLFSBLOCK)) {
 		xfs_iroot_realloc(ip, -1, whichfork);
+		ASSERT(ifp->if_broot == NULL);
+		XFS_IFORK_FMT_SET(ip, whichfork, XFS_DINODE_FMT_EXTENTS);
 		xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
 		return -ENOSPC;
 	}
-- 
2.17.1