From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CF25915CAC for ; Tue, 8 Nov 2022 13:51:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F3F0C433C1; Tue, 8 Nov 2022 13:51:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1667915493; bh=/sB7xKj7T3vXXsjWW7Qq6aoAXcjhvWgXNGcrzwpYhWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nXORvCYcbmdF/ZY6Q3PVsNHg45+ck74sGLDSH6marEkjhojUb5f6rOd8Tg9DWQ55V Yzt1uMH2WVBWCSTH10Y55GWwXObJLd7YO8uXPP8E41R1UGM78IIHgxNwABiZodGg9y kt/X7ixxk8pXbMSmcseRg4Uj8rjr7xdrP8FM//jE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Rasmus Villemoes , Willy Tarreau , "Paul E. McKenney" Subject: [PATCH 5.4 51/74] tools/nolibc/string: Fix memcmp() implementation Date: Tue, 8 Nov 2022 14:39:19 +0100 Message-Id: <20221108133335.850656530@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221108133333.659601604@linuxfoundation.org> References: <20221108133333.659601604@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Rasmus Villemoes 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(-) --- a/tools/include/nolibc/nolibc.h +++ b/tools/include/nolibc/nolibc.h @@ -2318,9 +2318,9 @@ 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;