From patchwork Mon Jul 29 13:49:00 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lukas Wunner X-Patchwork-Id: 815119 Received: from mailout1.hostsharing.net (mailout1.hostsharing.net [83.223.95.204]) (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 BBEBE1E515; Mon, 29 Jul 2024 14:09:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=83.223.95.204 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722262177; cv=none; b=L2AHy2BK94rgEUnrWEBzERzvnn21YB6EVo85PWUQSP8jrn+v6pPa7UIivb5A7vbJjmVSfOESp4KC8v2K33lulYJmSGTXwdRlq+EblyRKrW65Y4EAMPm1vWxFZa3Rzj+oYyNYNtdG5u2RMOeZL2k1g6HnmRWLEYmkhUseheEiNKc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722262177; c=relaxed/simple; bh=RcAAJ8fmfX2NcwwdaRaXyVBwYdu794CqKr587/Wkr2A=; h=Message-ID:In-Reply-To:References:From:Date:Subject:To:Cc; b=D7SLyur4PytigjLan+pWSNUpz2Mx0FGCC6RHQH3c7C0hVZtbuyupdPXQdAimnYWy65t8sFvs30USHpwf44qGd7OxkFC5e6b9FY/Gs6ujZIFNY6toLTyqIB3Ubkh+0FiIlE2zXGzf1iPWqihMZ5LSvRkeGT2O0Q7KAEBCKcbHG1U= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de; spf=pass smtp.mailfrom=wunner.de; arc=none smtp.client-ip=83.223.95.204 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=wunner.de Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by mailout1.hostsharing.net (Postfix) with ESMTPS id B04DC101917BB; Mon, 29 Jul 2024 16:09:32 +0200 (CEST) Received: from localhost (unknown [89.246.108.87]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by h08.hostsharing.net (Postfix) with ESMTPSA id 8383562FAD29; Mon, 29 Jul 2024 16:09:32 +0200 (CEST) X-Mailbox-Line: From 919ce5664ab3883f1bc15aadfc6b6a2d9b30ecbd Mon Sep 17 00:00:00 2001 Message-ID: <919ce5664ab3883f1bc15aadfc6b6a2d9b30ecbd.1722260176.git.lukas@wunner.de> In-Reply-To: References: From: Lukas Wunner Date: Mon, 29 Jul 2024 15:49:00 +0200 Subject: [PATCH 3/5] crypto: ecdsa - Avoid signed integer overflow on signature decoding To: Herbert Xu , "David S. Miller" , Stefan Berger Cc: David Howells , Vitaly Chikunov , Tadeusz Struk , Andrew Zaborowski , Saulo Alessandre , Jonathan Cameron , linux-crypto@vger.kernel.org, keyrings@vger.kernel.org Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: When extracting a signature component r or s from an ASN.1-encoded integer, ecdsa_get_signature_rs() subtracts the expected length "bufsize" from the ASN.1 length "vlen" (both of unsigned type size_t) and stores the result in "diff" (of signed type ssize_t). This results in a signed integer overflow if vlen > SSIZE_MAX + bufsize. The kernel is compiled with -fno-strict-overflow, which implies -fwrapv, meaning signed integer overflow is not undefined behavior. And the function does check for overflow: if (-diff >= bufsize) return -EINVAL; So the code is fine in principle but not very obvious. In the future it might trigger a false-positive with CONFIG_UBSAN_SIGNED_WRAP=y. Avoid by comparing the two unsigned variables directly and erroring out if "vlen" is too large. Signed-off-by: Lukas Wunner Reviewed-by: Stefan Berger Reviewed-by: Jonathan Cameron --- crypto/ecdsa.c | 17 ++++------------- 1 file changed, 4 insertions(+), 13 deletions(-) diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index f63731fb7535..03f608132242 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -35,29 +35,20 @@ static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag, const void *value, size_t vlen, unsigned int ndigits) { size_t bufsize = ndigits * sizeof(u64); - ssize_t diff = vlen - bufsize; const char *d = value; - if (!value || !vlen) + if (!value || !vlen || vlen > bufsize + 1) return -EINVAL; - /* diff = 0: 'value' has exacly the right size - * diff > 0: 'value' has too many bytes; one leading zero is allowed that - * makes the value a positive integer; error on more - * diff < 0: 'value' is missing leading zeros - */ - if (diff > 0) { + if (vlen > bufsize) { /* skip over leading zeros that make 'value' a positive int */ if (*d == 0) { vlen -= 1; - diff--; d++; - } - if (diff) + } else { return -EINVAL; + } } - if (-diff >= bufsize) - return -EINVAL; ecc_digits_from_bytes(d, vlen, dest, ndigits);