From d8ded8f4724c83279823231b65c9bac2deb62d40 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Fri, 21 Oct 2022 08:01:53 +0200 Subject: [PATCH] tools/nolibc/string: Fix memcmp() implementation The C standard says that memcmp() must treat the buffers as consisting of "unsigned chars". If char happens to be unsigned, the casts are ok, but then obviously the c1 variable can never contain a negative value. And when char is signed, the casts are wrong, and there's still a problem with using an 8-bit quantity to hold the difference, because that can range from -255 to +255. For example, assuming char is signed, comparing two 1-byte buffers, one containing 0x00 and another 0x80, the current implementation would return -128 for both memcmp(a, b, 1) and memcmp(b, a, 1), whereas one of those should of course return something positive. Signed-off-by: Rasmus Villemoes Fixes: 6c9adb75b7b3 ("rcutorture: Import a copy of nolibc") Cc: stable@vger.kernel.org # v5.0+ Signed-off-by: Willy Tarreau Signed-off-by: Paul E. McKenney --- tools/include/nolibc/string.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h index 718a405ffbc38..ad97c0d522b8e 100644 --- a/tools/include/nolibc/string.h +++ b/tools/include/nolibc/string.h @@ -19,9 +19,9 @@ static __attribute__((unused)) int memcmp(const void *s1, const void *s2, size_t n) { size_t ofs = 0; - char c1 = 0; + int c1 = 0; - while (ofs < n && !(c1 = ((char *)s1)[ofs] - ((char *)s2)[ofs])) { + while (ofs < n && !(c1 = ((unsigned char *)s1)[ofs] - ((unsigned char *)s2)[ofs])) { ofs++; } return c1; -- 2.39.5