lib/string_kunit: add correctness test for strrchr()

Add a KUnit test for strrchr() 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@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20260130025018.172925-4-jiangfeng@kylinos.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 1c2d57e056249849b6e650ce81f8963a60dd0b26..2bed641e1eaeb7756bd61e364b63ad69595966e0 100644 (file)
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -190,6 +190,36 @@ static void string_test_strchr(struct kunit *test)
        KUNIT_ASSERT_NULL(test, result);
 }
 
+static void string_test_strrchr(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_PTR_EQ(test, strrchr(s, 'Z'), NULL);
+
+                       if (len > 0)
+                               KUNIT_EXPECT_PTR_EQ(test, strrchr(s, 'A'), s + len - 1);
+                       else
+                               KUNIT_EXPECT_PTR_EQ(test, strrchr(s, 'A'), NULL);
+
+                       s[len] = 'A';
+               }
+       }
+
+       vfree(buf);
+}
+
 static void string_test_strnchr(struct kunit *test)
 {
        const char *test_string = "abcdefghijkl";
@@ -685,6 +715,7 @@ static struct kunit_case string_test_cases[] = {
        KUNIT_CASE(string_test_strnlen),
        KUNIT_CASE(string_test_strchr),
        KUNIT_CASE(string_test_strnchr),
+       KUNIT_CASE(string_test_strrchr),
        KUNIT_CASE(string_test_strspn),
        KUNIT_CASE(string_test_strcmp),
        KUNIT_CASE(string_test_strcmp_long_strings),