From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH net v2] net: sctp: fix ipv6 ipsec encryption bug in sctp_v6_xmit Date: Wed, 11 Sep 2013 11:30:16 -0400 Message-ID: <52308C88.10604@gmail.com> References: <1378911516-15942-1-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-sctp@vger.kernel.org, adobriyan@gmail.com, Steffen Klassert , Hannes Frederic Sowa To: Daniel Borkmann Return-path: Received: from mail-ie0-f176.google.com ([209.85.223.176]:57978 "EHLO mail-ie0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753854Ab3IKPaU (ORCPT ); Wed, 11 Sep 2013 11:30:20 -0400 In-Reply-To: <1378911516-15942-1-git-send-email-dborkman@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 09/11/2013 10:58 AM, Daniel Borkmann wrote: > Alan Chester reported an issue with IPv6 on SCTP that IPsec traffic is not > being encrypted, whereas on IPv4 it is. Setting up an AH + ESP transport > does not seem to have the desired effect: > > SCTP + IPv4: > > 22:14:20.809645 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto AH (51), length 116) > 192.168.0.2 > 192.168.0.5: AH(spi=0x00000042,sumlen=16,seq=0x1): ESP(spi=0x00000044,seq=0x1), length 72 > 22:14:20.813270 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto AH (51), length 340) > 192.168.0.5 > 192.168.0.2: AH(spi=0x00000043,sumlen=16,seq=0x1): > > SCTP + IPv6: > > 22:31:19.215029 IP6 (class 0x02, hlim 64, next-header SCTP (132) payload length: 364) > fe80::222:15ff:fe87:7fc.3333 > fe80::92e6:baff:fe0d:5a54.36767: sctp > 1) [INIT ACK] [init tag: 747759530] [rwnd: 62464] [OS: 10] [MIS: 10] > > Moreover, Alan says: > > This problem was seen with both Racoon and Racoon2. Other people have seen > this with OpenSwan. When IPsec is configured to encrypt all upper layer > protocols the SCTP connection does not initialize. After using Wireshark to > follow packets, this is because the SCTP packet leaves Box A unencrypted and > Box B believes all upper layer protocols are to be encrypted so it drops > this packet, causing the SCTP connection to fail to initialize. When IPsec > is configured to encrypt just SCTP, the SCTP packets are observed unencrypted. > > In fact, using `socat sctp6-listen:3333 -` on one end and transferring "plaintext" > string on the other end, results in cleartext on the wire where SCTP eventually > does not report any errors, thus in the latter case that Alan reports, the > non-paranoid user might think he's communicating over an encrypted transport on > SCTP although he's not (tcpdump ... -X): > > ... > 0x0030: 5d70 8e1a 0003 001a 177d eb6c 0000 0000 ]p.......}.l.... > 0x0040: 0000 0000 706c 6169 6e74 6578 740a 0000 ....plaintext... > > Only in /proc/net/xfrm_stat we can see XfrmInTmplMismatch increasing on the > receiver side. Initial follow-up analysis from Alan's bug report was done by > Alexey Dobriyan. Also thanks to Vlad Yasevich for feedback on this. > > SCTP has its own implementation of sctp_v6_xmit() not calling inet6_csk_xmit(). > This has the implication that it probably never really got updated along with > changes in inet6_csk_xmit() and therefore does not seem to invoke xfrm handlers. > > SCTP's IPv4 xmit however, properly calls ip_queue_xmit() to do the work. Since > a call to inet6_csk_xmit() would solve this problem, but result in unecessary > route lookups, let us just use the cached flowi6 instead that we got through > sctp_v6_get_dst(). Since all SCTP packets are being sent through sctp_packet_transmit(), > we do the route lookup / flow caching in sctp_transport_route(), hold it in > tp->dst and skb_dst_set() right after that. If we would alter fl6->daddr in > sctp_v6_xmit() to np->opt->srcrt, we possibly could run into the same effect > of not having xfrm layer pick it up, hence, use fl6_update_dst() in sctp_v6_get_dst() > instead to get the correct source routed dst entry, which we assign to the skb. > > Also source address routing example from 625034113 ("sctp: fix sctp to work with > ipv6 source address routing") still works with this patch! Nevertheless, in RFC5095 > it is actually 'recommended' to not use that anyway due to traffic amplification [1]. > So it seems we're not supposed to do that anyway in sctp_v6_xmit(). Moreover, if > we overwrite the flow destination here, the lower IPv6 layer will be unable to > put the correct destination address into IP header, as routing header is added in > ipv6_push_nfrag_opts() but then probably with wrong final destination. Things aside, > result of this patch is that we do not have any XfrmInTmplMismatch increase plus on > the wire with this patch it now looks like: > > SCTP + IPv6: > > 08:17:47.074080 IP6 2620:52:0:102f:7a2b:cbff:fe27:1b0a > 2620:52:0:102f:213:72ff:fe32:7eba: > AH(spi=0x00005fb4,seq=0x1): ESP(spi=0x00005fb5,seq=0x1), length 72 > 08:17:47.074264 IP6 2620:52:0:102f:213:72ff:fe32:7eba > 2620:52:0:102f:7a2b:cbff:fe27:1b0a: > AH(spi=0x00003d54,seq=0x1): ESP(spi=0x00003d55,seq=0x1), length 296 > > This fixes Kernel Bugzilla 24412. This security issue seems to be present since > 2.6.18 kernels. Lets just hope some big passive adversary in the wild didn't have > its fun with that. lksctp-tools IPv6 regression test suite passes as well with > this patch. > > [1] http://www.secdev.org/conf/IPv6_RH_security-csw07.pdf > > Reported-by: Alan Chester > Reported-by: Alexey Dobriyan > Signed-off-by: Daniel Borkmann > Cc: Steffen Klassert > Cc: Hannes Frederic Sowa Acked-by: Vlad Yasevich -vlad > --- > v1->v2: > - use cached flow > - improved commit msg > > net/sctp/ipv6.c | 42 +++++++++++++----------------------------- > 1 file changed, 13 insertions(+), 29 deletions(-) > > diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c > index da613ce..4f52e2c 100644 > --- a/net/sctp/ipv6.c > +++ b/net/sctp/ipv6.c > @@ -204,44 +204,23 @@ out: > in6_dev_put(idev); > } > > -/* Based on tcp_v6_xmit() in tcp_ipv6.c. */ > static int sctp_v6_xmit(struct sk_buff *skb, struct sctp_transport *transport) > { > struct sock *sk = skb->sk; > struct ipv6_pinfo *np = inet6_sk(sk); > - struct flowi6 fl6; > - > - memset(&fl6, 0, sizeof(fl6)); > - > - fl6.flowi6_proto = sk->sk_protocol; > - > - /* Fill in the dest address from the route entry passed with the skb > - * and the source address from the transport. > - */ > - fl6.daddr = transport->ipaddr.v6.sin6_addr; > - fl6.saddr = transport->saddr.v6.sin6_addr; > - > - fl6.flowlabel = np->flow_label; > - IP6_ECN_flow_xmit(sk, fl6.flowlabel); > - if (ipv6_addr_type(&fl6.saddr) & IPV6_ADDR_LINKLOCAL) > - fl6.flowi6_oif = transport->saddr.v6.sin6_scope_id; > - else > - fl6.flowi6_oif = sk->sk_bound_dev_if; > - > - if (np->opt && np->opt->srcrt) { > - struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt; > - fl6.daddr = *rt0->addr; > - } > + struct flowi6 *fl6 = &transport->fl.u.ip6; > > pr_debug("%s: skb:%p, len:%d, src:%pI6 dst:%pI6\n", __func__, skb, > - skb->len, &fl6.saddr, &fl6.daddr); > + skb->len, &fl6->saddr, &fl6->daddr); > > - SCTP_INC_STATS(sock_net(sk), SCTP_MIB_OUTSCTPPACKS); > + IP6_ECN_flow_xmit(sk, fl6->flowlabel); > > if (!(transport->param_flags & SPP_PMTUD_ENABLE)) > skb->local_df = 1; > > - return ip6_xmit(sk, skb, &fl6, np->opt, np->tclass); > + SCTP_INC_STATS(sock_net(sk), SCTP_MIB_OUTSCTPPACKS); > + > + return ip6_xmit(sk, skb, fl6, np->opt, np->tclass); > } > > /* Returns the dst cache entry for the given source and destination ip > @@ -254,10 +233,12 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr, > struct dst_entry *dst = NULL; > struct flowi6 *fl6 = &fl->u.ip6; > struct sctp_bind_addr *bp; > + struct ipv6_pinfo *np = inet6_sk(sk); > struct sctp_sockaddr_entry *laddr; > union sctp_addr *baddr = NULL; > union sctp_addr *daddr = &t->ipaddr; > union sctp_addr dst_saddr; > + struct in6_addr *final_p, final; > __u8 matchlen = 0; > __u8 bmatchlen; > sctp_scope_t scope; > @@ -281,7 +262,8 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr, > pr_debug("src=%pI6 - ", &fl6->saddr); > } > > - dst = ip6_dst_lookup_flow(sk, fl6, NULL, false); > + final_p = fl6_update_dst(fl6, np->opt, &final); > + dst = ip6_dst_lookup_flow(sk, fl6, final_p, false); > if (!asoc || saddr) > goto out; > > @@ -333,10 +315,12 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr, > } > } > rcu_read_unlock(); > + > if (baddr) { > fl6->saddr = baddr->v6.sin6_addr; > fl6->fl6_sport = baddr->v6.sin6_port; > - dst = ip6_dst_lookup_flow(sk, fl6, NULL, false); > + final_p = fl6_update_dst(fl6, np->opt, &final); > + dst = ip6_dst_lookup_flow(sk, fl6, final_p, false); > } > > out: >