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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 AB1D5C48BD1 for ; Fri, 11 Jun 2021 14:54:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F3C2613F3 for ; Fri, 11 Jun 2021 14:54:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231231AbhFKO43 (ORCPT ); Fri, 11 Jun 2021 10:56:29 -0400 Received: from mail.netfilter.org ([217.70.188.207]:37320 "EHLO mail.netfilter.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230508AbhFKO43 (ORCPT ); Fri, 11 Jun 2021 10:56:29 -0400 Received: from netfilter.org (unknown [90.77.255.23]) by mail.netfilter.org (Postfix) with ESMTPSA id BED2D6423A; Fri, 11 Jun 2021 16:53:14 +0200 (CEST) Date: Fri, 11 Jun 2021 16:54:26 +0200 From: Pablo Neira Ayuso To: Phil Sutter , netfilter-devel@vger.kernel.org, Florian Westphal Subject: Re: [nf-next PATCH] netfilter: nft_exthdr: Search chunks in SCTP packets only Message-ID: <20210611145426.GA6760@salvia> References: <20210610142316.24354-1-phil@nwl.cc> <20210610174334.GA24536@salvia> <20210611102624.GI22614@orbyte.nwl.cc> <20210611115654.GA6356@salvia> <20210611125248.GL22614@orbyte.nwl.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210611125248.GL22614@orbyte.nwl.cc> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Fri, Jun 11, 2021 at 02:52:48PM +0200, Phil Sutter wrote: > On Fri, Jun 11, 2021 at 01:56:54PM +0200, Pablo Neira Ayuso wrote: > > On Fri, Jun 11, 2021 at 12:26:24PM +0200, Phil Sutter wrote: > > > On Thu, Jun 10, 2021 at 07:43:34PM +0200, Pablo Neira Ayuso wrote: > > > > On Thu, Jun 10, 2021 at 04:23:16PM +0200, Phil Sutter wrote: > > > > > Since user space does not generate a payload dependency, plain sctp > > > > > chunk matches cause searching in non-SCTP packets, too. Avoid this > > > > > potential mis-interpretation of packet data by checking pkt->tprot. > > > > > > > > > > Fixes: 133dc203d77df ("netfilter: nft_exthdr: Support SCTP chunks") > > > > > Signed-off-by: Phil Sutter > > > > > --- > > > > > net/netfilter/nft_exthdr.c | 5 ++++- > > > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c > > > > > index 7f705b5c09de8..1093bb83f8aeb 100644 > > > > > --- a/net/netfilter/nft_exthdr.c > > > > > +++ b/net/netfilter/nft_exthdr.c > > > > > @@ -312,6 +312,9 @@ static void nft_exthdr_sctp_eval(const struct nft_expr *expr, > > > > > const struct sctp_chunkhdr *sch; > > > > > struct sctp_chunkhdr _sch; > > > > > > > > > > + if (!pkt->tprot_set || pkt->tprot != IPPROTO_SCTP) > > > > > + goto err; > > > > > > > > nft_set_pktinfo_unspec() already initializes pkt->tprot to zero. > > > > > > > > I think it's safe to simplify this to: > > > > > > > > if (pkt->tprot != IPPROTO_SCTP) > > > > > > Are you sure? Checking the spots that (should) initialize > > > tprot/tprot_set, in nft_do_chain_inet() it seems that if state->pf is > > > neither NFPROTO_IPV4 nor NFPROTO_IPV6, nft_do_chain() is called without > > > prior init. Maybe default case should call nft_set_pktinfo_unspec()? > > > > state->pf in nft_do_chain_inet() can only be either NFPROTO_IPV4 or > > NFPROTO_IPV6. > > Shouldn't there be a WARN_ON_ONCE or something in the default case then? > Looking at nf_hook(), it seems entirely possible to me that state->pf > might be NFPROTO_ARP, for instance. That's probably just me not getting > it, but things we rely upon shouldn't be hidden that well, right? nft_do_chain_inet() is called from the NFPROTO_INET hook, which results in either NFPROTO_IPV4 or NFPROTO_IPV6. This is hot path, I would not add more code there. The default case is just there to avoid a warning from gcc. Probably a comment like /* Should not ever happen */ for the default case in nft_do_chain_inet() is fine with you? :) > > pkt->tprot_set is there to deal with a corner case: IPPROTO_IP (0). > > If pkt->tprot_set == true and pkt->tprot == 0, it means: "match on > > IPPROTO_IP". For other IPPROTO_*, checking pkt->tprot looks safe to me. > > Ah, thanks for clarifying! So whenever I check a specific value that's > non-zero, tprot_set doesn't matter. Should I send a patch for the same > change in nft_tcp_header_pointer(), too? (That's where I copied the code > from. ;) I think so, that's fine indeed.