[PATCH 6/7] mm/damon/core-kunit: skip wrong quota goal walk in commit_quota_goals()

[SJ Park]

damos_test_commit_quota_goals_for() traverses damos quota goals after
damos_commit_quota_goals() call.  It assumes damos_commit_quota_goals()
made expected numbers of goals.  It might not.  Because the traversal is
made based on destination struct length, it could do out of bounds
access for source 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 goals 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: d9adfb8a28e7 ("mm/damon/tests/core-kunit: add damos_commit_quota_goals() test")
Cc: <stable@xxxxxxxxxxxxxxx> # 6.19.x
Signed-off-by: SJ Park <sj@xxxxxxxxxx>
---
 mm/damon/tests/core-kunit.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index ca6ac12a15b24..c0fc903a6a259 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -839,6 +839,7 @@ static void damos_test_commit_quota_goals_for(struct kunit *test,
 	struct damos_quota_goal *goal, *next;
 	bool skip = true;
 	int i;
+	int nr_dst = 0, nr_src = 0;
 
 	INIT_LIST_HEAD(&dst.goals);
 	INIT_LIST_HEAD(&src.goals);
@@ -861,6 +862,14 @@ static void damos_test_commit_quota_goals_for(struct kunit *test,
 
 	damos_commit_quota_goals(&dst, &src);
 
+	damos_for_each_quota_goal(goal, &dst)
+		nr_dst++;
+	damos_for_each_quota_goal(goal, &src)
+		nr_src++;
+	KUNIT_EXPECT_EQ(test, nr_dst, nr_src);
+	if (nr_dst != nr_src)
+		goto out;
+
 	i = 0;
 	damos_for_each_quota_goal(goal, (&dst)) {
 		KUNIT_EXPECT_EQ(test, goal->metric, src_goals[i].metric);
-- 
2.47.3