[PATCH 6.6.y] xfs: strengthen the "is cow staging" helpers in scrub

[Sasha Levin <sashal@kernel.org>]

From: "Darrick J. Wong" <djwong@kernel.org>

[ Upstream commit 0d43368844a75ad13561a1198a3b027940730756 ]

LOLLM pointed out a bug in both of the refcount scrub predicates that
determine if a range of blocks is marked as CoW staging in the btree.
While it compares blockcount < len, this isn't enough to determine that
the CoW staging record is at least as large as the range passed into the
helper.  Fix both of them.

Cc: stable@vger.kernel.org # v4.16
Fixes: f6d5fc21fdc713 ("xfs: cross-reference refcount btree during scrub")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
[ Omitted the rtrefcount.c hunk because Linux 6.12 lacks realtime refcount scrub support. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/xfs/scrub/refcount.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/refcount.c b/fs/xfs/scrub/refcount.c
index 304ea1e1bfb08..807785a2e2467 100644
--- a/fs/xfs/scrub/refcount.c
+++ b/fs/xfs/scrub/refcount.c
@@ -569,8 +569,12 @@ xchk_xref_is_cow_staging(
 	if (rc.rc_domain != XFS_REFC_DOMAIN_COW)
 		xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
 
+	/* Can't start after bno */
+	if (rc.rc_startblock > agbno)
+		xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
+
 	/* Must be at least as long as what was passed in */
-	if (rc.rc_blockcount < len)
+	if (rc.rc_startblock + rc.rc_blockcount < agbno + len)
 		xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
 }
 
-- 
2.53.0