[PATCH 1/1][T/X/B] xfs: don't fail when converting shortform attr to long form during ATTR_REPLACE

[Tyler Hicks]

From: "Darrick J. Wong" <darrick.wong at oracle.com>

Kanda Motohiro reported that expanding a tiny xattr into a large xattr
fails on XFS because we remove the tiny xattr from a shortform fork and
then try to re-add it after converting the fork to extents format having
not removed the ATTR_REPLACE flag.  This fails because the attr is no
longer present, causing a fs shutdown.

This is derived from the patch in his bug report, but we really
shouldn't ignore a nonzero retval from the remove call.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199119
Reported-by: kanda.motohiro at gmail.com
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>

CVE-2018-18690

(cherry picked from commit 7b38460dc8e4eafba06c78f8e37099d3b34d473c)
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 fs/xfs/libxfs/xfs_attr.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index a76914db72ef..e4265db08e4b 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -511,7 +511,14 @@ xfs_attr_shortform_addname(xfs_da_args_t *args)
 		if (args->flags & ATTR_CREATE)
 			return retval;
 		retval = xfs_attr_shortform_remove(args);
-		ASSERT(retval == 0);
+		if (retval)
+			return retval;
+		/*
+		 * Since we have removed the old attr, clear ATTR_REPLACE so
+		 * that the leaf format add routine won't trip over the attr
+		 * not being around.
+		 */
+		args->flags &= ~ATTR_REPLACE;
 	}
 
 	if (args->namelen >= XFS_ATTR_SF_ENTSIZE_MAX ||
-- 
2.7.4