[PATCH v6 2/8] lib/string_kunit: add correctness test for strnlen()

[Feng Jiang]

Add a KUnit test for strnlen() to verify correctness across
different string lengths and memory alignments. Use vmalloc()
to place the NUL character at the page boundary to ensure
over-reads are detected.

Suggested-by: Andy Shevchenko <andy at kernel.org>
Suggested-by: Kees Cook <kees at kernel.org>
Signed-off-by: Feng Jiang <jiangfeng at kylinos.cn>
---
 lib/tests/string_kunit.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 335f2e6c2ed6..886d21d32fa9 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -132,6 +132,40 @@ static void string_test_strlen(struct kunit *test)
 	vfree(buf);
 }
 
+static void string_test_strnlen(struct kunit *test)
+{
+	size_t buf_size;
+	char *buf, *s;
+
+	buf_size = PAGE_ALIGN(STRING_TEST_MAX_LEN + STRING_TEST_MAX_OFFSET + 1);
+	buf = vmalloc(buf_size);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+	memset(buf, 'A', buf_size);
+
+	for (size_t offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
+		for (size_t len = 0; len <= STRING_TEST_MAX_LEN; len++) {
+			s = buf + buf_size - 1 - offset - len;
+			s[len] = '\0';
+
+			if (len > 0)
+				KUNIT_EXPECT_EQ(test, strnlen(s, len - 1), len - 1);
+			if (len > 1)
+				KUNIT_EXPECT_EQ(test, strnlen(s, len - 2), len - 2);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s, len), len);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 1), len);
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 2), len);
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 10), len);
+
+			s[len] = 'A';
+		}
+	}
+
+	vfree(buf);
+}
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -647,6 +681,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset32),
 	KUNIT_CASE(string_test_memset64),
 	KUNIT_CASE(string_test_strlen),
+	KUNIT_CASE(string_test_strnlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strspn),
-- 
2.25.1