From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: Re: [PATCH net] ipv6: Prevent ipv6_find_hdr() from returning ENOENT for valid non-first fragments Date: Fri, 9 Jan 2015 12:45:06 +0100 Message-ID: <20150109114506.GA4857@salvia> References: <20150106224706.GA7416@salvia> <1420627396.26870.36.camel@stressinduktion.org> <20150108205328.GA3361@salvia> <1420756756.1755002.211556745.0418D128@webmail.messagingengine.com> <20150109000546.GA3488@salvia> <1420803255.1978819.211762005.707EFFB9@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Rahul Sharma , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org To: Hannes Frederic Sowa Return-path: Content-Disposition: inline In-Reply-To: <1420803255.1978819.211762005.707EFFB9@webmail.messagingengine.com> Sender: netdev-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org Hi Hannes, On Fri, Jan 09, 2015 at 12:34:15PM +0100, Hannes Frederic Sowa wrote: > On Fri, Jan 9, 2015, at 08:18, Rahul Sharma wrote: > > Hi Pablo, > > > > On Fri, Jan 9, 2015 at 5:35 AM, Pablo Neira Ayuso > > wrote: > > > On Thu, Jan 08, 2015 at 11:39:16PM +0100, Hannes Frederic Sowa wrote: > > >> Hi Pablo, > > >> > > >> On Thu, Jan 8, 2015, at 21:53, Pablo Neira Ayuso wrote: > > >> > I'm afraid we cannot just get rid of that !ipv6_ext_hdr() check. The > > >> > ipv6_find_hdr() function is designed to return the transport protocol. > > >> > After the proposed change, it will return extension header numbers. > > >> > This will break existing ip6tables rulesets since the `-p' option > > >> > relies on this function to match the transport protocol. > > >> > > > >> > Note that the AH header is skipped (see code a bit below this > > >> > problematic fragmentation handling) so the follow up header after the > > >> > AH header is returned as the transport header. > > >> > > > >> > We can probably return the AH protocol number for non-1st fragments. > > >> > However, that would be something new to ip6tables since nobody has > > >> > ever seen packet matching `-p ah' rules. Thus, we restore control to > > >> > the user to allow this, but we would accept all kind of fragmented AH > > >> > traffic through the firewall since we cannot know what transport > > >> > protocol contains from non-1st fragments (unless I'm missing anything, > > >> > I need to have a closer look at this again tomorrow with fresher > > >> > mind). > > >> > > >> The code in question is guarded by (_frag_off != 0), so we are > > >> definitely processing a non-1st fragment currently. The -p match would > > >> happen at the time when the packet is reassembled and thus ipv6_find_hdr > > >> will find the real transport (final) header at this point (I hope I > > >> followed the code correctly here). > > > > > > Then, Rahul should get things working by modprobing nf_defrag_ipv6. > > > > I already had nf_defrag_ipv6 installed when the issue occured. But I > > see ip6table_raw_hook returning NF_DROP for the second fragment. > > That's what I expected. I think the change only affects hooks before > reassembly. reassembly happens at NF_IP6_PRI_CONNTRACK_DEFRAG (-400), so that happens before NF_IP6_PRI_RAW (-300) in IPv6 which is where the raw table is placed.