[PATCH 7/7] mm/damon/core-kunit: skip wrong region walk in commit_target_regions()

[SJ Park]

damon_test_commit_target_regions_for() traverses expected values array
after damon_commit_target_regions() call.  It assumes
damon_commit_target_regions() made expected number of regions.  It might
not.  Because the traversal is made based on the region count, it could
do out of bounds access to the expectation value array.

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 testing if the number of regions was also changed as expected
and exit early for the failure.

The issue was discovered [1] by Sashiko.

[1] https://lore.kernel.org/20260713144757.39740-1-sj@xxxxxxxxxx

Fixes: 603f67eb91e0 ("mm/damon/tests/core-kunit: add damon_commit_target_regions() test")
Cc: <stable@xxxxxxxxxxxxxxx> # 6.19.x
Signed-off-by: SJ Park <sj@xxxxxxxxxx>
---
 mm/damon/tests/core-kunit.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index c0fc903a6a259..805d15a64500d 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1277,14 +1277,19 @@ static void damon_test_commit_target_regions_for(struct kunit *test,
 		kunit_skip(test, "src target setup fail");
 	}
 	damon_commit_target_regions(dst_target, src_target, 1);
+
+	KUNIT_EXPECT_EQ(test, damon_nr_regions(dst_target), nr_expect_regions);
+	if (damon_nr_regions(dst_target) != nr_expect_regions)
+		goto out;
+
 	i = 0;
 	damon_for_each_region(r, dst_target) {
 		KUNIT_EXPECT_EQ(test, r->ar.start, expect_start_end[i][0]);
 		KUNIT_EXPECT_EQ(test, r->ar.end, expect_start_end[i][1]);
 		i++;
 	}
-	KUNIT_EXPECT_EQ(test, damon_nr_regions(dst_target), nr_expect_regions);
-	KUNIT_EXPECT_EQ(test, i, nr_expect_regions);
+
+out:
 	damon_free_target(dst_target);
 	damon_free_target(src_target);
 }
-- 
2.47.3