[PATCH] Allow receiving packets on the fallback tunnel if they pass sanity checks

[Phil Dibowitz <phil@ipom.com>]

Ville Nuorvala wrote this patch to solve a problem we were having at Facebook.
He hasn't had time to send it upstream yet, but gave me permission to do it,
and I want to make sure it makes it upstream by World v6 Launch Day.

>From b413062771afbba064ae9bc49b5daed7abb1243d Mon Sep 17 00:00:00 2001
From: Ville Nuorvala <ville.nuorvala@gmail.com>
Subject: [PATCH] Allow receiving packets on the fallback tunnel if they pass sanity checks

The same IPv6 address checks are performed as with any normal tunnel,
but as the fallback tunnel endpoint addresses are unspecified, the checks
must be performed on a per-packet basis, rather than at tunnel
configuration time.

Signed-off-by: Ville Nuorvala <ville.nuorvala@gmail.com>
Tested-by: Phil Dibowitz <phil@ipom.com>

---
 include/net/ip6_tunnel.h |    2 +
 net/ipv6/ip6_tunnel.c    |   65 +++++++++++++++++++++++++++-------------------
 2 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h
index fc73e66..358fb86 100644
--- a/include/net/ip6_tunnel.h
+++ b/include/net/ip6_tunnel.h
@@ -9,6 +9,8 @@
 #define IP6_TNL_F_CAP_XMIT 0x10000
 /* capable of receiving packets */
 #define IP6_TNL_F_CAP_RCV 0x20000
+/* determine capability on a per-packet basis */
+#define IP6_TNL_F_CAP_PER_PACKET 0x40000
 
 /* IPv6 tunnel */
 
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index c9015fa..04a3cba 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -684,24 +684,50 @@ static void ip6ip6_dscp_ecn_decapsulate(const struct ip6_tnl *t,
 		IP6_ECN_set_ce(ipv6_hdr(skb));
 }
 
+static __u32 ip6_tnl_get_cap(struct ip6_tnl *t,
+			     const struct in6_addr *laddr,
+			     const struct in6_addr *raddr)
+{
+	struct ip6_tnl_parm *p = &t->parms;
+	int ltype = ipv6_addr_type(laddr);
+	int rtype = ipv6_addr_type(raddr);
+	__u32 flags = 0;
+
+	if (ltype == IPV6_ADDR_ANY || rtype == IPV6_ADDR_ANY) {
+		flags = IP6_TNL_F_CAP_PER_PACKET;
+	} else if (ltype & (IPV6_ADDR_UNICAST|IPV6_ADDR_MULTICAST) &&
+		   rtype & (IPV6_ADDR_UNICAST|IPV6_ADDR_MULTICAST) &&
+		   !((ltype|rtype) & IPV6_ADDR_LOOPBACK) &&
+		   (!((ltype|rtype) & IPV6_ADDR_LINKLOCAL) || p->link)) {
+		if (ltype&IPV6_ADDR_UNICAST)
+			flags |= IP6_TNL_F_CAP_XMIT;
+		if (rtype&IPV6_ADDR_UNICAST)
+			flags |= IP6_TNL_F_CAP_RCV;
+	}
+	return flags;
+}
+
 /* called with rcu_read_lock() */
-static inline int ip6_tnl_rcv_ctl(struct ip6_tnl *t)
+static inline int ip6_tnl_rcv_ctl(struct ip6_tnl *t,
+				  const struct in6_addr *laddr,
+				  const struct in6_addr *raddr)
 {
 	struct ip6_tnl_parm *p = &t->parms;
 	int ret = 0;
 	struct net *net = dev_net(t->dev);
 
-	if (p->flags & IP6_TNL_F_CAP_RCV) {
+	if ((p->flags & IP6_TNL_F_CAP_RCV) ||
+	    ((p->flags & IP6_TNL_F_CAP_PER_PACKET) &&
+	     (ip6_tnl_get_cap(t, laddr, raddr) & IP6_TNL_F_CAP_RCV))) {
 		struct net_device *ldev = NULL;
 
 		if (p->link)
 			ldev = dev_get_by_index_rcu(net, p->link);
 
-		if ((ipv6_addr_is_multicast(&p->laddr) ||
-		     likely(ipv6_chk_addr(net, &p->laddr, ldev, 0))) &&
-		    likely(!ipv6_chk_addr(net, &p->raddr, NULL, 0)))
+		if ((ipv6_addr_is_multicast(laddr) ||
+		     likely(ipv6_chk_addr(net, laddr, ldev, 0))) &&
+		    likely(!ipv6_chk_addr(net, raddr, NULL, 0)))
 			ret = 1;
-
 	}
 	return ret;
 }
@@ -740,7 +766,7 @@ static int ip6_tnl_rcv(struct sk_buff *skb, __u16 protocol,
 			goto discard;
 		}
 
-		if (!ip6_tnl_rcv_ctl(t)) {
+		if (!ip6_tnl_rcv_ctl(t, &ipv6h->daddr, &ipv6h->saddr)) {
 			t->dev->stats.rx_dropped++;
 			rcu_read_unlock();
 			goto discard;
@@ -1114,25 +1140,6 @@ tx_err:
 	return NETDEV_TX_OK;
 }
 
-static void ip6_tnl_set_cap(struct ip6_tnl *t)
-{
-	struct ip6_tnl_parm *p = &t->parms;
-	int ltype = ipv6_addr_type(&p->laddr);
-	int rtype = ipv6_addr_type(&p->raddr);
-
-	p->flags &= ~(IP6_TNL_F_CAP_XMIT|IP6_TNL_F_CAP_RCV);
-
-	if (ltype & (IPV6_ADDR_UNICAST|IPV6_ADDR_MULTICAST) &&
-	    rtype & (IPV6_ADDR_UNICAST|IPV6_ADDR_MULTICAST) &&
-	    !((ltype|rtype) & IPV6_ADDR_LOOPBACK) &&
-	    (!((ltype|rtype) & IPV6_ADDR_LINKLOCAL) || p->link)) {
-		if (ltype&IPV6_ADDR_UNICAST)
-			p->flags |= IP6_TNL_F_CAP_XMIT;
-		if (rtype&IPV6_ADDR_UNICAST)
-			p->flags |= IP6_TNL_F_CAP_RCV;
-	}
-}
-
 static void ip6_tnl_link_config(struct ip6_tnl *t)
 {
 	struct net_device *dev = t->dev;
@@ -1153,7 +1160,8 @@ static void ip6_tnl_link_config(struct ip6_tnl *t)
 	if (!(p->flags&IP6_TNL_F_USE_ORIG_FLOWLABEL))
 		fl6->flowlabel |= IPV6_FLOWLABEL_MASK & p->flowinfo;
 
-	ip6_tnl_set_cap(t);
+	p->flags &= ~(IP6_TNL_F_CAP_XMIT|IP6_TNL_F_CAP_RCV|IP6_TNL_F_CAP_PER_PACKET);
+	p->flags |= ip6_tnl_get_cap(t, &p->laddr, &p->raddr);
 
 	if (p->flags&IP6_TNL_F_CAP_XMIT && p->flags&IP6_TNL_F_CAP_RCV)
 		dev->flags |= IFF_POINTOPOINT;
@@ -1438,6 +1446,9 @@ static int __net_init ip6_fb_tnl_dev_init(struct net_device *dev)
 
 	t->parms.proto = IPPROTO_IPV6;
 	dev_hold(dev);
+
+	ip6_tnl_link_config(t);
+
 	rcu_assign_pointer(ip6n->tnls_wc[0], t);
 	return 0;
 }

-- 
Phil Dibowitz                             phil@ipom.com
Open Source software and tech docs        Insanity Palace of Metallica
http://www.phildev.net/                   http://www.ipom.com/

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