From: Darrick J. Wong <darrick.wong@oracle.com>
Date: Fri, 26 Aug 2016 01:16:41 +0000 (+1000)
Subject: xfs: don't perform lookups on zero-height btrees
X-Git-Tag: v4.8.0-rc1~18
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=574b41535bd2b2a07b5ffdf466a6bb4585907f3e;p=thirdparty%2Fxfsprogs-dev.git

xfs: don't perform lookups on zero-height btrees

If the caller passes in a cursor to a zero-height btree (which is
impossible), we never set block to anything but NULL, which causes the
later dereference of it to crash.  Instead, just return -EFSCORRUPTED.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
---

diff --git a/libxfs/xfs_btree.c b/libxfs/xfs_btree.c
index 8391078f3..cb671f654 100644
--- a/libxfs/xfs_btree.c
+++ b/libxfs/xfs_btree.c
@@ -1810,6 +1810,10 @@ xfs_btree_lookup(
 
 	XFS_BTREE_STATS_INC(cur, lookup);
 
+	/* No such thing as a zero-level tree. */
+	if (cur->bc_nlevels == 0)
+		return -EFSCORRUPTED;
+
 	block = NULL;
 	keyno = 0;