From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2E84C43613 for ; Fri, 21 Jun 2019 13:04:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC2E7206B7 for ; Fri, 21 Jun 2019 13:04:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726311AbfFUNEO (ORCPT ); Fri, 21 Jun 2019 09:04:14 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45162 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726299AbfFUNEO (ORCPT ); Fri, 21 Jun 2019 09:04:14 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5LCvAeM024481 for ; Fri, 21 Jun 2019 09:04:13 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0b-001b2d01.pphosted.com with ESMTP id 2t8x7n48ev-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 21 Jun 2019 09:04:12 -0400 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 21 Jun 2019 14:04:09 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5LD48NM54001774 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 21 Jun 2019 13:04:08 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 124C6A4059; Fri, 21 Jun 2019 13:04:08 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 68E18A404D; Fri, 21 Jun 2019 13:04:07 +0000 (GMT) Received: from localhost.localdomain (unknown [9.80.81.152]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 21 Jun 2019 13:04:07 +0000 (GMT) Subject: Re: [PATCH v5 01/11] ima-evm-utils: Make sure sig buffer is always MAX_SIGNATURE_SIZE From: Mimi Zohar To: Vitaly Chikunov Cc: Mimi Zohar , Dmitry Kasatkin , linux-integrity@vger.kernel.org Date: Fri, 21 Jun 2019 09:03:56 -0400 In-Reply-To: <20190621122833.xzy3ztzr2ilmium6@altlinux.org> References: <20190618135623.6861-1-vt@altlinux.org> <20190618135623.6861-2-vt@altlinux.org> <1561066938.4057.18.camel@linux.ibm.com> <20190621065913.a3plltlinylkdkeb@altlinux.org> <1561115292.4057.70.camel@linux.ibm.com> <20190621112225.sf6rtxzc2pu4oyfh@altlinux.org> <1561116450.4057.81.camel@linux.ibm.com> <20190621122833.xzy3ztzr2ilmium6@altlinux.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 (3.20.5-1.fc24) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19062113-0012-0000-0000-0000032B37DA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19062113-0013-0000-0000-0000216461D4 Message-Id: <1561122236.4057.107.camel@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-21_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906210108 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri, 2019-06-21 at 15:28 +0300, Vitaly Chikunov wrote: > Mimi, > > On Fri, Jun 21, 2019 at 07:27:30AM -0400, Mimi Zohar wrote: > > On Fri, 2019-06-21 at 14:22 +0300, Vitaly Chikunov wrote: > > > On Fri, Jun 21, 2019 at 07:08:12AM -0400, Mimi Zohar wrote: > > > > On Fri, 2019-06-21 at 09:59 +0300, Vitaly Chikunov wrote: > > > > > On Thu, Jun 20, 2019 at 05:42:18PM -0400, Mimi Zohar wrote: > > > > > > On Tue, 2019-06-18 at 16:56 +0300, Vitaly Chikunov wrote: > > > > > > > Fix off-by-one error of the output buffer passed to sign_hash(). > > > > > > > > > > > > > > Signed-off-by: Vitaly Chikunov > > > > > > > --- > > > > > > > src/evmctl.c | 4 ++-- > > > > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > diff --git a/src/evmctl.c b/src/evmctl.c > > > > > > > index 15a7226..03f41fe 100644 > > > > > > > --- a/src/evmctl.c > > > > > > > +++ b/src/evmctl.c > > > > > > > @@ -510,7 +510,7 @@ static int calc_evm_hash(const char *file, unsigned char *hash) > > > > > > > static int sign_evm(const char *file, const char *key) > > > > > > > { > > > > > > > unsigned char hash[MAX_DIGEST_SIZE]; > > > > > > > - unsigned char sig[MAX_SIGNATURE_SIZE]; > > > > > > > + unsigned char sig[MAX_SIGNATURE_SIZE + 1]; > > > > > > > int len, err; > > > > > > > > > > > > > > len = calc_evm_hash(file, hash); > > > > > > > @@ -519,7 +519,7 @@ static int sign_evm(const char *file, const char *key) > > > > > > > return len; > > > > > > > > > > > > > > len = sign_hash(params.hash_algo, hash, len, key, NULL, sig + 1); > > > > > > > - assert(len < sizeof(sig)); > > > > > > > + assert(len <= MAX_SIGNATURE_SIZE); > > > > > > > if (len <= 1) > > > > > > > return len; > > > > > > > > > > > > > > > > > > > A similar problem occurs in sign_ima.  Without these changes > > > > > > sign_hash() succeeds, returning a length of 520 for > > > > > > sha256/streebog256. > > > > > > > > > > I will add it. Also, I found more similar errors and will fix them together. > > > > > > > > The first byte of sig is reserved for the type of signature.  The > > > > remaining buffer is for the signature itself.  The existing > > > > "assert(len < sizeof(sig))" is therefore correct.  The sig size being > > > > returned is less than 1023, so why is this change needed? > > > > > > Well, it looked more straightforward to check explicit > > > MAX_SIGNATURE_SIZE instead of relying on that '<' accounts for > > > that additional byte. > > > > > > Main fix is of course this: > > > > > > > > > > - unsigned char sig[MAX_SIGNATURE_SIZE]; > > > > > > > + unsigned char sig[MAX_SIGNATURE_SIZE + 1]; > > > > That is the question.  Why does the buffer need to be > > "MAX_SIGNATURE_SIZE + 1", making it 1025 bytes?  MAX_SIGNATURE_SIZE - > > 1 is large enough for the signature. > > Because maximum signature size is supposed to be MAX_SIGNATURE_SIZE, > isn't it? Why in reality it should be some other value? No, I think it was chosen as an upper bound, simply used for buffer bounds checking.  I wouldn't make sig 1025.  If you want to make MAX_SIGNATuRE_SIZE 1023 and keep the + 1, that would be fine. > > That give me idea to add check if a generated signature will fit into > `sig` (assuming it's of MAX_SIGNATURE_SIZE) in sign_hash_v2() before we > call EVP_PKEY_sign(). Yes, a call to EVP_PKEY_sign(), without providing the "sig", will return the length.  evmctl can be called recursively (-r).  I would hope that EVP_PKEY_sign() would check the buffer size before calculating the sig.  If it does, then checking is duplication.  I'm a bit concerned about the performance impact of checking the sig size each time. Mimi