string: Convert strscpy() self-test to KUnit

Convert the strscpy() self-test to a KUnit test.

Cc: David Gow <davidgow@google.com>
Cc: Tobin C. Harding <tobin@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/lkml/Y072ZMk/hNkfwqMv@dev-arch.thelio-3990X
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 129 insertions, 0 deletions

diff --git a/lib/strscpy_kunit.c b/lib/strscpy_kunit.c
new file mode 100644
index 000000000000..98523f828d3a
--- /dev/null
+++ b/lib/strscpy_kunit.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Kernel module for testing 'strscpy' family of functions.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/string.h>
+
+/*
+ * tc() - Run a specific test case.
+ * @src: Source string, argument to strscpy_pad()
+ * @count: Size of destination buffer, argument to strscpy_pad()
+ * @expected: Expected return value from call to strscpy_pad()
+ * @terminator: 1 if there should be a terminating null byte 0 otherwise.
+ * @chars: Number of characters from the src string expected to be
+ *         written to the dst buffer.
+ * @pad: Number of pad characters expected (in the tail of dst buffer).
+ *       (@pad does not include the null terminator byte.)
+ *
+ * Calls strscpy_pad() and verifies the return value and state of the
+ * destination buffer after the call returns.
+ */
+static void tc(struct kunit *test, char *src, int count, int expected,
+	       int chars, int terminator, int pad)
+{
+	int nr_bytes_poison;
+	int max_expected;
+	int max_count;
+	int written;
+	char buf[6];
+	int index, i;
+	const char POISON = 'z';
+
+	KUNIT_ASSERT_TRUE_MSG(test, src != NULL,
+			      "null source string not supported");
+
+	memset(buf, POISON, sizeof(buf));
+	/* Future proofing test suite, validate args */
+	max_count = sizeof(buf) - 2; /* Space for null and to verify overflow */
+	max_expected = count - 1;    /* Space for the null */
+
+	KUNIT_ASSERT_LE_MSG(test, count, max_count,
+		"count (%d) is too big (%d) ... aborting", count, max_count);
+	KUNIT_EXPECT_LE_MSG(test, expected, max_expected,
+		"expected (%d) is bigger than can possibly be returned (%d)",
+		expected, max_expected);
+
+	written = strscpy_pad(buf, src, count);
+	KUNIT_ASSERT_EQ(test, written, expected);
+
+	if (count && written == -E2BIG) {
+		KUNIT_ASSERT_EQ_MSG(test, 0, strncmp(buf, src, count - 1),
+			"buffer state invalid for -E2BIG");
+		KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
+			"too big string is not null terminated correctly");
+	}
+
+	for (i = 0; i < chars; i++)
+		KUNIT_ASSERT_EQ_MSG(test, buf[i], src[i],
+			"buf[i]==%c != src[i]==%c", buf[i], src[i]);
+
+	if (terminator)
+		KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
+			"string is not null terminated correctly");
+
+	for (i = 0; i < pad; i++) {
+		index = chars + terminator + i;
+		KUNIT_ASSERT_EQ_MSG(test, buf[index], '\0',
+			"padding missing at index: %d", i);
+	}
+
+	nr_bytes_poison = sizeof(buf) - chars - terminator - pad;
+	for (i = 0; i < nr_bytes_poison; i++) {
+		index = sizeof(buf) - 1 - i; /* Check from the end back */
+		KUNIT_ASSERT_EQ_MSG(test, buf[index], POISON,
+			"poison value missing at index: %d", i);
+	}
+}
+
+static void strscpy_test(struct kunit *test)
+{
+	/*
+	 * tc() uses a destination buffer of size 6 and needs at
+	 * least 2 characters spare (one for null and one to check for
+	 * overflow).  This means we should only call tc() with
+	 * strings up to a maximum of 4 characters long and 'count'
+	 * should not exceed 4.  To test with longer strings increase
+	 * the buffer size in tc().
+	 */
+
+	/* tc(test, src, count, expected, chars, terminator, pad) */
+	tc(test, "a", 0, -E2BIG, 0, 0, 0);
+	tc(test, "",  0, -E2BIG, 0, 0, 0);
+
+	tc(test, "a", 1, -E2BIG, 0, 1, 0);
+	tc(test, "",  1, 0,	 0, 1, 0);
+
+	tc(test, "ab", 2, -E2BIG, 1, 1, 0);
+	tc(test, "a",  2, 1,	  1, 1, 0);
+	tc(test, "",   2, 0,	  0, 1, 1);
+
+	tc(test, "abc", 3, -E2BIG, 2, 1, 0);
+	tc(test, "ab",  3, 2,	   2, 1, 0);
+	tc(test, "a",   3, 1,	   1, 1, 1);
+	tc(test, "",    3, 0,	   0, 1, 2);
+
+	tc(test, "abcd", 4, -E2BIG, 3, 1, 0);
+	tc(test, "abc",  4, 3,	    3, 1, 0);
+	tc(test, "ab",   4, 2,	    2, 1, 1);
+	tc(test, "a",    4, 1,	    1, 1, 2);
+	tc(test, "",     4, 0,	    0, 1, 3);
+}
+
+static struct kunit_case strscpy_test_cases[] = {
+	KUNIT_CASE(strscpy_test),
+	{}
+};
+
+static struct kunit_suite strscpy_test_suite = {
+	.name = "strscpy",
+	.test_cases = strscpy_test_cases,
+};
+
+kunit_test_suite(strscpy_test_suite);
+
+MODULE_AUTHOR("Tobin C. Harding <tobin@kernel.org>");
+MODULE_LICENSE("GPL");