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 DF8FE18CC1C; Sun, 24 Nov 2024 12:45:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452319; cv=none; b=j+CLJ/RalFS9E4oPxtJEFpRbvLodibfCSHC0CeH0Tln0hyLyopNC+G+wtZ12AEyaV7r0/aAqhbXkPoUA3Eg2q5brjU5SqAzyQE7+R3BlMewCdwusOViu1AZJzTJ7vBOODnfM2FN3rPJbKORTENddyjOxdPyuopobmMFFOve9skk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452319; c=relaxed/simple; bh=oirgsQnHBfGFNBrWVg1xmJLEkU3WZRxplluiMQ+96mc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=ZQlxT+zqyDDzvz7uxwHPnt/y0+5pRJmroTcFUnDTqMxsMrkL70Ysig/0AyTHOBvLt6TXodAzYvjrjn0d4COlYNWk0tG9MXnp6ONcn96Mo49iSffq43b6pmEFTlgxSQmGASmFrzozYE4lgwKG0C1qWSmKNGbLAKiKyG8vWRYhL88= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TBNRls1O; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TBNRls1O" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B5F0C4CECC; Sun, 24 Nov 2024 12:45:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452318; bh=oirgsQnHBfGFNBrWVg1xmJLEkU3WZRxplluiMQ+96mc=; h=From:To:Cc:Subject:Date:From; b=TBNRls1OTpbIZsa3DtJaC6aT9U5xvRKNhAr0lBffagq/oDK4XAyVYg9Y0tSNOHnP5 r/Zj6+E9zcZYk/xWQYUF30rJZ7AS+WuBsmga7u1PPl68ZYR+3J9giyh2eBl+Do8lPE //yYhzn2PdrZFsYAnHhYa1NBZgbWg+HNPDmKBvhjdCZPxCts0/uexa4V8dMSa5SyUN WwN4ogy1TdrnuN9Wbf2yqhYTwpcGB5+v7C2tgVK7eaPyEgWrJIc2mjx+2SK1mfyg26 8mUzfpC5z7XAnhPgjFEffnFnvUeC+WlJA4Qja36eyeYrnSZ/3fvnx0D/kFParBudnO wiC2wDUtvSBKg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Lukas Wunner , Stefan Berger , Jonathan Cameron , Herbert Xu , Sasha Levin , davem@davemloft.net, linux-crypto@vger.kernel.org Subject: [PATCH AUTOSEL 6.12 1/6] crypto: ecdsa - Avoid signed integer overflow on signature decoding Date: Sun, 24 Nov 2024 07:45:06 -0500 Message-ID: <20241124124516.3337485-1-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.12.1 Content-Transfer-Encoding: 8bit From: Lukas Wunner [ Upstream commit 3b0565c703503f832d6cd7ba805aafa3b330cb9d ] 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 Signed-off-by: Herbert Xu Signed-off-by: Sasha Levin --- crypto/ecdsa.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index d5a10959ec281..80ef16ae6a40b 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -36,29 +36,24 @@ 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); -- 2.43.0