[PATCH AUTOSEL 4.19 106/206] xfs: don't ever return a stale pointer from __xfs_dir3_free_read

From: Sasha Levin
Date: Thu Sep 17 2020 - 22:45:38 EST

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

[ Upstream commit 1cb5deb5bc095c070c09a4540c45f9c9ba24be43 ]

If we decide that a directory free block is corrupt, we must take care
not to leak a buffer pointer to the caller. After xfs_trans_brelse
returns, the buffer can be freed or reused, which means that we have to
set *bpp back to NULL.

Callers are supposed to notice the nonzero return value and not use the
buffer pointer, but we should code more defensively, even if all current
callers handle this situation correctly.

Fixes: de14c5f541e7 ("xfs: verify free block header fields")
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
fs/xfs/libxfs/xfs_dir2_node.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/xfs/libxfs/xfs_dir2_node.c b/fs/xfs/libxfs/xfs_dir2_node.c
index f1bb3434f51c7..01e99806b941f 100644
--- a/fs/xfs/libxfs/xfs_dir2_node.c
+++ b/fs/xfs/libxfs/xfs_dir2_node.c
@@ -214,6 +214,7 @@ __xfs_dir3_free_read(
if (fa) {
xfs_verifier_error(*bpp, -EFSCORRUPTED, fa);
xfs_trans_brelse(tp, *bpp);
+ *bpp = NULL;