From 27b4406f9c35bb1fe9049fdd833d36665fc2b077 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 commit b3f4f51ea68a495f8a5956064c33dce711a2df91 upstream. 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: 66b6f755ad45 ("rcutorture: Import a copy of nolibc") Cc: stable@vger.kernel.org # v5.0+ Signed-off-by: Willy Tarreau Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman --- tools/include/nolibc/nolibc.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h index 3e2c6f2ed587..d64020c1922c 100644 --- a/tools/include/nolibc/nolibc.h +++ b/tools/include/nolibc/nolibc.h @@ -2408,9 +2408,9 @@ 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;