mm/damon/core-kunit: skip wrong dest walk in commit_dests_for()

damos_test_commit_dests_for() traverse damos action destinations after
damos_commit_dests().  It assumes damos_commit_dests() made expected
numbers of destinations for source and destination structures.  It might
not.  Because the traversal is made based on destination struct length, it
could do out of bounds access for source value expectation.

The consequent user impact (out-of-bound access ) is quite bad.  The
realistic user impact would be limited, though.  It would affect only test
run setups.

Fix it by exiting early for the number of regions test failure.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260718001442.87129-6-sj@kernel.org
Link: https://lore.kernel.org/20260713144757.39740-1-sj@kernel.org [1]
Fixes: eec573b8dd65 ("mm/damon/tests/core-kunit: add damos_commit_dests() test")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: <stable@vger.kernel.org> # 6.19.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index eddf3a048458..9b8c20a50ad5 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1008,6 +1008,8 @@ static void damos_test_commit_dests_for(struct kunit *test,
 	skip = false;
 
 	KUNIT_EXPECT_EQ(test, dst.nr_dests, src_nr_dests);
+	if (dst.nr_dests != src_nr_dests)
+		goto out;
 	for (i = 0; i < dst.nr_dests; i++) {
 		KUNIT_EXPECT_EQ(test, dst.node_id_arr[i], src_node_id_arr[i]);
 		KUNIT_EXPECT_EQ(test, dst.weight_arr[i], src_weight_arr[i]);