[PATCH 4.9 09/35] dm cache metadata: ignore hints array being too small during resize

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt@redhat.com>

commit 4561ffca88c546f96367f94b8f1e4715a9c62314 upstream.

Commit fd2fa9541 ("dm cache metadata: save in-core policy_hint_size to
on-disk superblock") enabled previously written policy hints to be
used after a cache is reactivated.  But in doing so the cache
metadata's hint array was left exposed to out of bounds access because
on resize the metadata's on-disk hint array wasn't ever extended.

Fix this by ignoring that there are no on-disk hints associated with the
newly added cache blocks.  An expanded on-disk hint array is later
rewritten upon the next clean shutdown of the cache.

Fixes: fd2fa9541 ("dm cache metadata: save in-core policy_hint_size to on-disk superblock")
Cc: stable@vger.kernel.org
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/dm-cache-metadata.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1262,8 +1262,8 @@ static int __load_mappings(struct dm_cac
 		if (hints_valid) {
 			r = dm_array_cursor_next(&cmd->hint_cursor);
 			if (r) {
-				DMERR("dm_array_cursor_next for hint failed");
-				goto out;
+				dm_array_cursor_end(&cmd->hint_cursor);
+				hints_valid = false;
 			}
 		}
 	}