ipv6:introduce function to find route for redirect

RFC 4861 says that the IP source address of the Redirect is the
same as the current first-hop router for the specified ICMP
Destination Address, so the gateway should be taken into
consideration when we find the route for redirect.

There was once a check in commit
a6279458c534d01ccc39498aba61c93083ee0372 ("NDISC: Search over
all possible rules on receipt of redirect.") and the check
went away in commit b94f1c0904da9b8bf031667afc48080ba7c3e8c9
("ipv6: Use icmpv6_notify() to propagate redirect, instead of
rt6_redirect()").

The bug is only "exploitable" on layer-2 because the source
address of the redirect is checked to be a valid link-local
address but it makes spoofing a lot easier in the same L2
domain nonetheless.

Thanks very much for Hannes's help.

Signed-off-by: Duan Jiong <duanj.fnst@cn.fujitsu.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

6 files changed, 81 insertions, 11 deletions

diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index bb02e176cb70..73784c3d4642 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -628,7 +628,7 @@ static void ah6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                 return;
 
         if (type == NDISC_REDIRECT)
-                ip6_redirect(skb, net, 0, 0);
+                ip6_redirect(skb, net, skb->dev->ifindex, 0);
         else
                 ip6_update_pmtu(skb, net, info, 0, 0);
         xfrm_state_put(x);
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index aeac0dc3635d..d3618a78fcac 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -447,7 +447,7 @@ static void esp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                 return;
 
         if (type == NDISC_REDIRECT)
-                ip6_redirect(skb, net, 0, 0);
+                ip6_redirect(skb, net, skb->dev->ifindex, 0);
         else
                 ip6_update_pmtu(skb, net, info, 0, 0);
         xfrm_state_put(x);
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 7cfc8d284870..73681c227453 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -92,7 +92,7 @@ static void icmpv6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
         if (type == ICMPV6_PKT_TOOBIG)
                 ip6_update_pmtu(skb, net, info, 0, 0);
         else if (type == NDISC_REDIRECT)
-                ip6_redirect(skb, net, 0, 0);
+                ip6_redirect(skb, net, skb->dev->ifindex, 0);
 
         if (!(type & ICMPV6_INFOMSG_MASK))
                 if (icmp6->icmp6_type == ICMPV6_ECHO_REQUEST)
diff --git a/net/ipv6/ipcomp6.c b/net/ipv6/ipcomp6.c
index 7af5aee75d98..5636a912074a 100644
--- a/net/ipv6/ipcomp6.c
+++ b/net/ipv6/ipcomp6.c
@@ -76,7 +76,7 @@ static void ipcomp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                 return;
 
         if (type == NDISC_REDIRECT)
-                ip6_redirect(skb, net, 0, 0);
+                ip6_redirect(skb, net, skb->dev->ifindex, 0);
         else
                 ip6_update_pmtu(skb, net, info, 0, 0);
         xfrm_state_put(x);
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 22210650596f..c4bc7a35cd56 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1367,7 +1367,8 @@ static void ndisc_redirect_rcv(struct sk_buff *skb)
                 return;
 
         if (!ndopts.nd_opts_rh) {
-                ip6_redirect_no_header(skb, dev_net(skb->dev), 0, 0);
+                ip6_redirect_no_header(skb, dev_net(skb->dev),
+                                        skb->dev->ifindex, 0);
                 return;
         }
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index b770085ae36d..c979dd96d82a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1156,6 +1156,77 @@ void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu)
 }
 EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu);
 
+/* Handle redirects */
+struct ip6rd_flowi {
+        struct flowi6 fl6;
+        struct in6_addr gateway;
+};
+
+static struct rt6_info *__ip6_route_redirect(struct net *net,
+                                             struct fib6_table *table,
+                                             struct flowi6 *fl6,
+                                             int flags)
+{
+        struct ip6rd_flowi *rdfl = (struct ip6rd_flowi *)fl6;
+        struct rt6_info *rt;
+        struct fib6_node *fn;
+
+        /* Get the "current" route for this destination and
+         * check if the redirect has come from approriate router.
+         *
+         * RFC 4861 specifies that redirects should only be
+         * accepted if they come from the nexthop to the target.
+         * Due to the way the routes are chosen, this notion
+         * is a bit fuzzy and one might need to check all possible
+         * routes.
+         */
+
+        read_lock_bh(&table->tb6_lock);
+        fn = fib6_lookup(&table->tb6_root, &fl6->daddr, &fl6->saddr);
+restart:
+        for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                if (rt6_check_expired(rt))
+                        continue;
+                if (rt->dst.error)
+                        break;
+                if (!(rt->rt6i_flags & RTF_GATEWAY))
+                        continue;
+                if (fl6->flowi6_oif != rt->dst.dev->ifindex)
+                        continue;
+                if (!ipv6_addr_equal(&rdfl->gateway, &rt->rt6i_gateway))
+                        continue;
+                break;
+        }
+
+        if (!rt)
+                rt = net->ipv6.ip6_null_entry;
+        else if (rt->dst.error) {
+                rt = net->ipv6.ip6_null_entry;
+                goto out;
+        }
+        BACKTRACK(net, &fl6->saddr);
+out:
+        dst_hold(&rt->dst);
+
+        read_unlock_bh(&table->tb6_lock);
+
+        return rt;
+};
+
+static struct dst_entry *ip6_route_redirect(struct net *net,
+                                        const struct flowi6 *fl6,
+                                        const struct in6_addr *gateway)
+{
+        int flags = RT6_LOOKUP_F_HAS_SADDR;
+        struct ip6rd_flowi rdfl;
+
+        rdfl.fl6 = *fl6;
+        rdfl.gateway = *gateway;
+
+        return fib6_rule_lookup(net, &rdfl.fl6,
+                                flags, __ip6_route_redirect);
+}
+
 void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark)
 {
         const struct ipv6hdr *iph = (struct ipv6hdr *) skb->data;
@@ -1170,9 +1241,8 @@ void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark)
         fl6.saddr = iph->saddr;
         fl6.flowlabel = ip6_flowinfo(iph);
 
-        dst = ip6_route_output(net, NULL, &fl6);
-        if (!dst->error)
-                rt6_do_redirect(dst, NULL, skb);
+        dst = ip6_route_redirect(net, &fl6, &ipv6_hdr(skb)->saddr);
+        rt6_do_redirect(dst, NULL, skb);
         dst_release(dst);
 }
 EXPORT_SYMBOL_GPL(ip6_redirect);
@@ -1192,9 +1262,8 @@ void ip6_redirect_no_header(struct sk_buff *skb, struct net *net, int oif,
         fl6.daddr = msg->dest;
         fl6.saddr = iph->daddr;
 
-        dst = ip6_route_output(net, NULL, &fl6);
-        if (!dst->error)
-                rt6_do_redirect(dst, NULL, skb);
+        dst = ip6_route_redirect(net, &fl6, &iph->saddr);
+        rt6_do_redirect(dst, NULL, skb);
         dst_release(dst);
 }