[PATCH v6 1/8] lib/string_kunit: add correctness test for strlen()

[Feng Jiang]

Add a KUnit test for strlen() 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: Kees Cook <kees at kernel.org>
Signed-off-by: Feng Jiang <jiangfeng at kylinos.cn>
---
 lib/tests/string_kunit.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index f9a8e557ba77..335f2e6c2ed6 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -10,6 +10,7 @@
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/vmalloc.h>
 
 #define STRCMP_LARGE_BUF_LEN 2048
 #define STRCMP_CHANGE_POINT 1337
@@ -17,6 +18,9 @@
 #define STRCMP_TEST_EXPECT_LOWER(test, fn, ...) KUNIT_EXPECT_LT(test, fn(__VA_ARGS__), 0)
 #define STRCMP_TEST_EXPECT_GREATER(test, fn, ...) KUNIT_EXPECT_GT(test, fn(__VA_ARGS__), 0)
 
+#define STRING_TEST_MAX_LEN	128
+#define STRING_TEST_MAX_OFFSET	16
+
 static void string_test_memset16(struct kunit *test)
 {
 	unsigned i, j, k;
@@ -104,6 +108,30 @@ static void string_test_memset64(struct kunit *test)
 	}
 }
 
+static void string_test_strlen(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';
+			KUNIT_EXPECT_EQ_MSG(test, strlen(s), len,
+				"offset:%zu len:%zu", offset, len);
+			s[len] = 'A';
+		}
+	}
+
+	vfree(buf);
+}
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -618,6 +646,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset16),
 	KUNIT_CASE(string_test_memset32),
 	KUNIT_CASE(string_test_memset64),
+	KUNIT_CASE(string_test_strlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strspn),
-- 
2.25.1