From: David Laight Date: Mon, 2 Mar 2026 10:17:58 +0000 (+0000) Subject: selftests/nolibc: Check that snprintf() doesn't write beyond the buffer end X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4ea2dedd502e2b4bfa8a47f2aaaaac4eab01e00d;p=thirdparty%2Fkernel%2Flinux.git selftests/nolibc: Check that snprintf() doesn't write beyond the buffer end Fill buf[] with known data and check the vsnprintf() doesn't write beyond the specified buffer length. Would have picked up the bug in field padding. Signed-off-by: David Laight Acked-by: Willy Tarreau Link: https://patch.msgid.link/20260302101815.3043-7-david.laight.linux@gmail.com Signed-off-by: Thomas Weißschuh --- diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c index 154cc5711a4c9..5dc0edfe8d9aa 100644 --- a/tools/testing/selftests/nolibc/nolibc-test.c +++ b/tools/testing/selftests/nolibc/nolibc-test.c @@ -1679,6 +1679,10 @@ static int expect_vfprintf(int llen, const char *expected, const char *fmt, ...) va_list args; ssize_t w, expected_len; + /* Fill and terminate buf[] to check for overlong/absent writes */ + memset(buf, 0xa5, sizeof(buf) - 1); + buf[sizeof(buf) - 1] = 0; + va_start(args, fmt); /* Limit buffer length to test truncation */ w = vsnprintf(buf, VFPRINTF_LEN + 1, fmt, args); @@ -1710,6 +1714,15 @@ static int expect_vfprintf(int llen, const char *expected, const char *fmt, ...) return 1; } + /* Check for any overwrites after the actual data. */ + while (++cmp_len < sizeof(buf) - 1) { + if ((unsigned char)buf[cmp_len] != 0xa5) { + llen += printf(" overwrote buf[%d] with 0x%x", cmp_len, buf[cmp_len]); + result(llen, FAIL); + return 1; + } + } + result(llen, OK); return 0; }