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: Mon, 12 Jan 2015 12:51:11 +0100 Message-ID: <20150112115111.GA3506@salvia> References: <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> <20150109114506.GA4857@salvia> <1420818636.31075.15.camel@stressinduktion.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Hannes Frederic Sowa , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org To: Rahul Sharma Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org On Mon, Jan 12, 2015 at 04:38:16PM +0530, Rahul Sharma wrote: > Hi Pablo, Hannes > > On Fri, Jan 9, 2015 at 9:20 PM, Hannes Frederic Sowa > wrote: > > On Fr, 2015-01-09 at 12:45 +0100, Pablo Neira Ayuso wrote: > >> 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. > > > > I tried to reproduce it, but couldn't get non-1st fragments getting > > dropped during traversal of the raw table. They get dropped earlier at > > during reassembly or pass. > > > > I agree with Pablo, I also would like to see more data. > > > > Thanks, > > Hannes > > > > > > I enabled pr_debug() and there was no error in nf_ct_frag6_gather(). > It seems to have defragmented the packet correctly. As expected, > ipv6_defrag() returns NF_STOLEN for the first packet after queuing it. > For the next fragment, ipv6_defrag() calls nf_ct_frag6_output() after > after reassembling it. nf_ct_frag6_output() doesn't exist anymore. You're using an old kernel, you should have started by telling so in your report. See 6aafeef ("netfilter: push reasm skb through instead of original frag skbs").