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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 4CC27C433DF for ; Thu, 20 Aug 2020 07:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3390620786 for ; Thu, 20 Aug 2020 07:15:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725798AbgHTHPs (ORCPT ); Thu, 20 Aug 2020 03:15:48 -0400 Received: from helcar.hmeau.com ([216.24.177.18]:48934 "EHLO fornost.hmeau.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725797AbgHTHPs (ORCPT ); Thu, 20 Aug 2020 03:15:48 -0400 Received: from gwarestrin.arnor.me.apana.org.au ([192.168.0.7]) by fornost.hmeau.com with smtp (Exim 4.92 #5 (Debian)) id 1k8enC-000612-KO; Thu, 20 Aug 2020 17:15:23 +1000 Received: by gwarestrin.arnor.me.apana.org.au (sSMTP sendmail emulation); Thu, 20 Aug 2020 17:15:22 +1000 Date: Thu, 20 Aug 2020 17:15:22 +1000 From: Herbert Xu To: trix@redhat.com Cc: davem@davemloft.net, smueller@chronox.de, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] crypto: drbg: check blocklen is non zero Message-ID: <20200820071522.GA21511@gondor.apana.org.au> References: <20200802171247.16558-1-trix@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200802171247.16558-1-trix@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Sun, Aug 02, 2020 at 10:12:47AM -0700, trix@redhat.com wrote: > From: Tom Rix > > Clang static analysis reports this error > > crypto/drbg.c:441:40: warning: Division by zero > padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg)); > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > > When drbg_bocklen fails it returns 0. > > if (drbg && drbg->core) > return drbg->core->blocklen_bytes; > return 0; Yes but it can only fail if the drbg is not instantiated. If you're hitting the generate path with an uninstantiated drbg you've got bigger problems than a divide by zero. So how is this even possible? Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt