Hi Pablo, Hannes On Fri, Jan 9, 2015 at 9:20 PM, Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx> 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 <pablo@xxxxxxxxxxxxx> >> > > 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. I checked skb->len inside nf_ct_frag6_output() and it implies that they were indeed reassembled. Now from what I follow from the code, this function seems to iterate over both the fragments with corresponding skb's and incrementing thresh(NF_IP6_PRI_CONNTRACK_DEFRAG) by 1 so the subsequent hooks (ip6table_raw_hook, ipv6_conntrack_in, ip6table_mangle_hook) should get called in order for both the fragments. This works fine for the first fragment as I had mentioned, but the ip6table_raw_hook returns NF_DROP for the second fragment. Please let me know if you need more inputs. Thanks, Rahul -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
