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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1687BECAAD8 for ; Thu, 1 Sep 2022 06:27:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233361AbiIAG1Q (ORCPT ); Thu, 1 Sep 2022 02:27:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51688 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233316AbiIAG1N (ORCPT ); Thu, 1 Sep 2022 02:27:13 -0400 Received: from mail-pf1-x42f.google.com (mail-pf1-x42f.google.com [IPv6:2607:f8b0:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 99AE7F8FCE for ; Wed, 31 Aug 2022 23:27:11 -0700 (PDT) Received: by mail-pf1-x42f.google.com with SMTP id l65so6232189pfl.8 for ; Wed, 31 Aug 2022 23:27:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc; bh=LUpbwDphPvtED1QTi1ZPW1+S2RNACcn+wb6hlFtY8XY=; b=WWTU4lWTW/7wYi2qJpDzYN8K/NLpv7PlWS5uBAJkKppb81ks8aUuyIiL+aXKUp7YnF YocMSdrWOvhufrkb5kbh/9BZJjVdEzZnGqmd7AB9AVSuhB8lMWZtfoVTtl6TvHeZJ81O bcvx1UIUBnuqv3cP2vYFz0K6ohytRF3RkufYE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=LUpbwDphPvtED1QTi1ZPW1+S2RNACcn+wb6hlFtY8XY=; b=JyCmglvh6Zq8zPd6+Ln4KDxJNUPud7//DOVS5pmQfDaxahFKvuXGB9eKdwFhKzf3Se PuL96cjXieJ8RteUhzmxp6akxqdCQv5z7N8Lb5lCs7OhlQQUMuduruheVyZyBE2OH+gF 1HFQ3hQNA7HJTBduaAIkdT2fNBk+3gosgvzFVrVRkdY1SLB1JwPcU5ZCDQ3D3fanQFQK aiJB3074/G+GLE2KqHw5AgpUcHOB80LDeGfgTQP59oalrMVeglepRsKPdlubgIX2/bFK J5bGdYa7jJpAtRJDOpakKpJMtWSz+hkzvfXtDo4SSo87f4QRqNIOLmWgwOHffKAq7pfQ Hw0A== X-Gm-Message-State: ACgBeo0V1y97Q5D9BghIJcqU37vrB0NNB8JT5V2y4q9w4tBzkj/CDkR8 kSH0fNEmZVGMkVM3qdhlgeM2og== X-Google-Smtp-Source: AA6agR5Ky2h+fMYEWE96VBtRDKYJx75ceGIbNnAxgjJV3/KyA3d0lDG2E0gucajihCuxLu510+QrZA== X-Received: by 2002:a05:6a00:a82:b0:530:2f3c:ec99 with SMTP id b2-20020a056a000a8200b005302f3cec99mr29438360pfl.53.1662013631087; Wed, 31 Aug 2022 23:27:11 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id q12-20020a170902a3cc00b0016d8d277c02sm12816467plb.25.2022.08.31.23.27.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Aug 2022 23:27:09 -0700 (PDT) Date: Wed, 31 Aug 2022 23:27:08 -0700 From: Kees Cook To: Jakub Kicinski Cc: "David S. Miller" , Eric Dumazet , Paolo Abeni , Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , syzbot , Yajun Deng , netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, Oliver Hartkopp , Harshit Mogalapalli , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 1/2] netlink: Bounds-check nlmsg_len() Message-ID: <202208312324.F2F8B28CA@keescook> References: <20220901030610.1121299-1-keescook@chromium.org> <20220901030610.1121299-2-keescook@chromium.org> <20220831201825.378d748d@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220831201825.378d748d@kernel.org> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Aug 31, 2022 at 08:18:25PM -0700, Jakub Kicinski wrote: > On Wed, 31 Aug 2022 20:06:09 -0700 Kees Cook wrote: > > static inline int nlmsg_len(const struct nlmsghdr *nlh) > > { > > - return nlh->nlmsg_len - NLMSG_HDRLEN; > > + u32 nlmsg_contents_len; > > + > > + if (WARN_ON_ONCE(check_sub_overflow(nlh->nlmsg_len, > > + (u32)NLMSG_HDRLEN, > > + &nlmsg_contents_len))) > > + return 0; > > + if (WARN_ON_ONCE(nlmsg_contents_len > INT_MAX)) > > + return INT_MAX; > > + return nlmsg_contents_len; > > We check the messages on input, making sure the length is valid wrt > skb->len, and sane, ie > NLMSG_HDRLEN. See netlink_rcv_skb(). > > Can we not, pretty please? :( This would catch corrupted values... Is the concern the growth in image size? The check_sub_overflow() isn't large at all -- it's just adding a single overflow bit test. The WARNs are heavier, but they're all out-of-line. -- Kees Cook