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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 BD512C352A3 for ; Sat, 15 Feb 2020 22:58:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 937DC2083B for ; Sat, 15 Feb 2020 22:58:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726340AbgBOW65 (ORCPT ); Sat, 15 Feb 2020 17:58:57 -0500 Received: from orbyte.nwl.cc ([151.80.46.58]:43626 "EHLO orbyte.nwl.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726275AbgBOW65 (ORCPT ); Sat, 15 Feb 2020 17:58:57 -0500 Received: from n0-1 by orbyte.nwl.cc with local (Exim 4.91) (envelope-from ) id 1j36Ol-0003XA-JN; Sat, 15 Feb 2020 23:58:55 +0100 Date: Sat, 15 Feb 2020 23:58:55 +0100 From: Phil Sutter To: Pablo Neira Ayuso Cc: netfilter-devel@vger.kernel.org Subject: Re: [libnftnl PATCH] src: Fix nftnl_assert() on data_len Message-ID: <20200215225855.GU20005@orbyte.nwl.cc> Mail-Followup-To: Phil Sutter , Pablo Neira Ayuso , netfilter-devel@vger.kernel.org References: <20200214172417.11217-1-phil@nwl.cc> <20200214173247.2wbrvcqilqfmcqq5@salvia> <20200214173450.GR20005@orbyte.nwl.cc> <20200214174200.4xrvnlb72qebtvnb@salvia> <20200215004311.GS20005@orbyte.nwl.cc> <20200215131713.5gwn4ayk2udjff33@salvia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200215131713.5gwn4ayk2udjff33@salvia> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Hi Pablo, On Sat, Feb 15, 2020 at 02:17:13PM +0100, Pablo Neira Ayuso wrote: > On Sat, Feb 15, 2020 at 01:43:11AM +0100, Phil Sutter wrote: > > Hi Pablo, > > > > On Fri, Feb 14, 2020 at 06:42:00PM +0100, Pablo Neira Ayuso wrote: > > > On Fri, Feb 14, 2020 at 06:34:50PM +0100, Phil Sutter wrote: > > > > On Fri, Feb 14, 2020 at 06:32:47PM +0100, Pablo Neira Ayuso wrote: > > > > > On Fri, Feb 14, 2020 at 06:24:17PM +0100, Phil Sutter wrote: > > > > > > Typical idiom for *_get_u*() getters is to call *_get_data() and make > > > > > > sure data_len matches what each of them is returning. Yet they shouldn't > > > > > > trust *_get_data() to write into passed pointer to data_len since for > > > > > > chains and NFTNL_CHAIN_DEVICES attribute, it does not. Make sure these > > > > > > assert() calls trigger in those cases. > > > > > > > > > > The intention to catch for unset attributes through the assertion, > > > > > right? > > > > > > > > No, this is about making sure that no wrong getter is called, e.g. > > > > nftnl_chain_get_u64() with e.g. NFTNL_CHAIN_HOOKNUM attribute which is > > > > only 32bits. > > > > > > I think it will also catch the case I'm asking. If attribute is unset, > > > then nftnl_chain_get_data() returns NULL and the assertion checks > > > data_len, which has not been properly initialized. > > > > With nftnl_assert() being (shortened): > > > > | #define nftnl_assert(val, attr, expr) \ > > | ((!val || expr) ? \ > > | (void)0 : __nftnl_assert_fail(attr, __FILE__, __LINE__)) > > > > Check for 'expr' (which is passed as 'data_len == sizeof()') > > will only happen if 'val' is not NULL. Callers then return like so: > > > > | return val ? *val : 0; > > > > This means that if you pass an unset attribute to the getter, it will > > simply return 0. > > Thanks for explaining, Phil. If the problem is just > NFTNL_CHAIN_DEVICES and NFTNL_FLOWTABLE_DEVICES, probably this is just > fine? So zero data-length is reversed for arrays and update > nftnl_assert() to skip data_len == 0, ie. > > > | #define nftnl_assert(val, attr, expr) \ > > | ((!val || data_len == 0 || expr) ? \ > > | (void)0 : __nftnl_assert_fail(attr, __FILE__, __LINE__)) Your proposed patch would allow to call e.g.: | nftnl_chain_get_u32(c, NFTNL_CHAIN_DEVICES) This would return (uint32_t)*(&c->dev_array[0]), I highly doubt we should allow this. Unless I miss something, it is certainly a programming error if someone calls any of the nftnl_chain_get_{u,s}* getters on NFTNL_CHAIN_DEVICES attribute. So aborting with error message in nftnl_assert() is not only OK but actually helpful, no? Cheers, Phil