[PATCH 2/2] mm/kasan/kunit: extend vmalloc OOB tests to cover vrealloc()

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

Extend the vmalloc_oob() test to validate OOB detection after
resizing vmalloc allocations with vrealloc().

The test now verifies that KASAN correctly poisons and unpoisons vmalloc
memory when allocations are shrunk and expanded, ensuring OOB accesses
are reliably detected after each resize.

Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 mm/kasan/kasan_test_c.c | 50 ++++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index 2cafca31b092..cc8fc479e13a 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1840,6 +1840,29 @@ static void vmalloc_helpers_tags(struct kunit *test)
 	vfree(ptr);
 }
 
+static void vmalloc_oob_helper(struct kunit *test, char *v_ptr, size_t size)
+{
+	/*
+	 * We have to be careful not to hit the guard page in vmalloc tests.
+	 * The MMU will catch that and crash us.
+	 */
+
+	/* Make sure in-bounds accesses are valid. */
+	v_ptr[0] = 0;
+	v_ptr[size - 1] = 0;
+
+	/*
+	 * An unaligned access past the requested vmalloc size.
+	 * Only generic KASAN can precisely detect these.
+	 */
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+		KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)v_ptr)[size]);
+
+	/* An aligned access into the first out-of-bounds granule. */
+	size = round_up(size, KASAN_GRANULE_SIZE);
+	KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)v_ptr)[size]);
+}
+
 static void vmalloc_oob(struct kunit *test)
 {
 	char *v_ptr, *p_ptr;
@@ -1856,24 +1879,21 @@ static void vmalloc_oob(struct kunit *test)
 
 	OPTIMIZER_HIDE_VAR(v_ptr);
 
-	/*
-	 * We have to be careful not to hit the guard page in vmalloc tests.
-	 * The MMU will catch that and crash us.
-	 */
+	vmalloc_oob_helper(test, v_ptr, size);
 
-	/* Make sure in-bounds accesses are valid. */
-	v_ptr[0] = 0;
-	v_ptr[size - 1] = 0;
+	size--;
+	v_ptr = vrealloc(v_ptr, size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, v_ptr);
 
-	/*
-	 * An unaligned access past the requested vmalloc size.
-	 * Only generic KASAN can precisely detect these.
-	 */
-	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
-		KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)v_ptr)[size]);
+	OPTIMIZER_HIDE_VAR(v_ptr);
 
-	/* An aligned access into the first out-of-bounds granule. */
-	KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)v_ptr)[size + 5]);
+	vmalloc_oob_helper(test, v_ptr, size);
+
+	size += 2;
+	v_ptr = vrealloc(v_ptr, size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, v_ptr);
+
+	vmalloc_oob_helper(test, v_ptr, size);
 
 	/* Check that in-bounds accesses to the physical page are valid. */
 	page = vmalloc_to_page(v_ptr);
-- 
2.52.0