From patchwork Tue Sep 10 14:30:24 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lukas Wunner X-Patchwork-Id: 827107 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 A41641A01CA; Tue, 10 Sep 2024 15:26:00 +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=1725981962; cv=none; b=Rav8VcPUzIrAktfYWc+w2LQYIb94d31hWvnjNIoLEcg475fqTI5agq6TD/kkx/+yI9ZV3rFO7/TmLydePXFf6/64+C9HfjsFv9Gn92/Q0OIKtazIioxXFe905uDG5FODXdO20NVFoNnWQeF3Zt2srUFhW1KcPkTC6jN7ZKpGDPM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725981962; c=relaxed/simple; bh=UuNWLOkpN2Kr6+gI0jyf4qB6UU6KAPybbT6dZ4y3R5w=; h=Message-ID:In-Reply-To:References:From:Date:Subject:To:Cc; b=sScP4DcSH5ZtPW/dPrQLgLqWkheeTAgaO17Hz5eghgTf/PiYqkQiN3an/1H81E310ILm05GV7OiiqavwX7dvb4I1N3B+MGHBxranUsbLOxoNSZGDjKc6KNikGWlt8uqyNL9D6oTFwPnzPL7CZPFqDrnyOV6nPWvudLZRx1WLy2c= 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 [IPv6:2a01:37:1000::53df:5f1c:0]) (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 8943D1019178F; Tue, 10 Sep 2024 17:25:58 +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 68DD360A8B01; Tue, 10 Sep 2024 17:25:58 +0200 (CEST) X-Mailbox-Line: From d5018797f813f8baae02954dabf6df167324fa75 Mon Sep 17 00:00:00 2001 Message-ID: In-Reply-To: References: From: Lukas Wunner Date: Tue, 10 Sep 2024 16:30:24 +0200 Subject: [PATCH v2 14/19] crypto: ecdsa - Avoid signed integer overflow on signature decoding To: Herbert Xu , "David S. Miller" , Eric Biggers , Stefan Berger , Vitaly Chikunov , Tadeusz Struk Cc: David Howells , Andrew Zaborowski , Saulo Alessandre , Jonathan Cameron , Ignat Korchagin , Marek Behun , Varad Gautam , Stephan Mueller , Denis Kenzior , 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 --- Changes v1 -> v2: * Add code comment explaining why vlen may be larger than bufsize (Stefan) crypto/ecdsa.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index 3b9873f56b0a..4a0ca93c99ea 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -35,29 +35,24 @@ 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 + /* + * vlen may be 1 byte larger than bufsize due to a leading zero byte + * (necessary if the most significant bit of the integer is set). */ - 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);