[PATCH v2 4/5] kasan: Avoid an unrelated RCU warning in the callback test

[Joel Fernandes]

rcu_uaf() passes a false protection condition to
rcu_dereference_protected(), which produces a suspicious-RCU-usage
warning before the intended KASAN failure occurs.

The pointer refers to a fresh allocation that has not been published to
readers. State that protection condition explicitly, leaving the intended
tests intact.

Test:
Built with CONFIG_KASAN_KUNIT_TEST=m
Booted Qemu guest (8 CPUs), ran modprobe kasan_test filtered to kasan.*rcu_uaf*

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
---
 mm/kasan/kasan_test_c.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index b9e167ed5be3..4e23765d722c 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -967,8 +967,9 @@ static void rcu_uaf(struct kunit *test)
 	ptr = kmalloc_obj(struct kasan_rcu_info);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	/* The freshly allocated object has not been published to readers. */
 	global_rcu_ptr = rcu_dereference_protected(
-				(struct kasan_rcu_info __rcu *)ptr, NULL);
+				(struct kasan_rcu_info __rcu *)ptr, true);
 
 	KUNIT_EXPECT_KASAN_FAIL_READ(test,
 			call_rcu(&global_rcu_ptr->rcu, rcu_uaf_reclaim);
-- 
2.54.0