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Date: Wed, 11 Sep 2013 11:30:16 -0400
From: Vlad Yasevich <vyasevich@...il.com>
To: Daniel Borkmann <dborkman@...hat.com>
CC: davem@...emloft.net, netdev@...r.kernel.org,
linux-sctp@...r.kernel.org, adobriyan@...il.com,
Steffen Klassert <steffen.klassert@...unet.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net v2] net: sctp: fix ipv6 ipsec encryption bug in sctp_v6_xmit
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 <alan.chester@...elec.com>
> Reported-by: Alexey Dobriyan <adobriyan@...il.com>
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
Acked-by: Vlad Yasevich <vyasevich@...il.com>
-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:
>
--
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