linux-kernel - [PATCH 30/32] selftests/nolibc: add test for snprintf() truncation

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Message-Id: <20250304-nolibc-kselftest-harness-v1-30-adca7cd231e2@linutronix.de>
Date: Tue, 04 Mar 2025 08:11:00 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Shuah Khan <shuah@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>, 
 Willy Tarreau <w@....eu>, 
 Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH 30/32] selftests/nolibc: add test for snprintf() truncation

Now that we have a proper snprintf() implementation,
make sure truncation is handled properly.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index a45fded42c14110c97c4c899d04dba8e676dfd49..0a891c40e2afbb398ae39b43dbe977efdab042e2 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1290,7 +1290,8 @@ static int expect_vfprintf(int llen, int c, const char *expected, const char *fm
 
 
 	va_start(args, fmt);
-	w = vsnprintf(buf, sizeof(buf), fmt, args);
+	/* Only allow writing 21 bytes, to test truncation */
+	w = vsnprintf(buf, 21, fmt, args);
 	va_end(args);
 
 	if (w != c) {
@@ -1396,6 +1397,7 @@ static int run_printf(int min, int max)
 		CASE_TEST(pointer);      EXPECT_VFPRINTF(3, "0x1", "%p", (void *) 0x1); break;
 		CASE_TEST(uintmax_t);    EXPECT_VFPRINTF(20, "18446744073709551615", "%ju", 0xffffffffffffffffULL); break;
 		CASE_TEST(intmax_t);     EXPECT_VFPRINTF(20, "-9223372036854775807", "%jd", 0x8000000000000001LL); break;
+		CASE_TEST(truncation);   EXPECT_VFPRINTF(25, "01234567890123456789", "%s", "0123456789012345678901234"); break;
 		CASE_TEST(scanf);        EXPECT_ZR(1, test_scanf()); break;
 		case __LINE__:
 			return ret; /* must be last */

-- 
2.48.1