Date:	Tue, 10 Sep 2013 20:05:16 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	davem@...emloft.net
Cc:	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: [PATCH net] net: sctp: fix ipv6 ipsec encryption bug in sctp_v6_xmit

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.

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. Hence,
lets do the same for IPv6 and invoke inet6_csk_xmit() [it does the same work
for us we do here manually anyway]; result 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.

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>
---
 net/sctp/ipv6.c | 34 ++++++++--------------------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index da613ce..74ba5ee 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -69,6 +69,7 @@
 #include <net/addrconf.h>
 #include <net/ip6_route.h>
 #include <net/inet_common.h>
+#include <net/inet6_connection_sock.h>
 #include <net/inet_ecn.h>
 #include <net/sctp/sctp.h>
 
@@ -209,39 +210,20 @@ 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;
-	}
+	/* This needs to explicitly done as we can have different transports. */
+	np->daddr = transport->ipaddr.v6.sin6_addr;
+	np->saddr = transport->saddr.v6.sin6_addr;
 
 	pr_debug("%s: skb:%p, len:%d, src:%pI6 dst:%pI6\n", __func__, skb,
-		 skb->len, &fl6.saddr, &fl6.daddr);
-
-	SCTP_INC_STATS(sock_net(sk), SCTP_MIB_OUTSCTPPACKS);
+		 skb->len, &np->saddr, &np->daddr);
 
 	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 inet6_csk_xmit(skb, NULL);
 }
 
 /* Returns the dst cache entry for the given source and destination ip
-- 
1.7.11.7

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