[IPSEC]: Add ICMP host relookup support

RFC 4301 requires us to relookup ICMP traffic that does not match any
policies using the reverse of its payload.  This patch implements this
for ICMP traffic that originates from or terminates on localhost.

This is activated on outbound with the new policy flag XFRM_POLICY_ICMP,
and on inbound by the new state flag XFRM_STATE_ICMP.

On inbound the policy check is now performed by the ICMP protocol so
that it can repeat the policy check where necessary.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 79 insertions, 3 deletions

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 13d7459..3c41a6f 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -92,6 +92,7 @@
 #include <asm/system.h>
 #include <asm/uaccess.h>
 #include <net/checksum.h>
+#include <net/xfrm.h>
 
 /*
  *	Build xmit assembly blocks
@@ -563,11 +564,71 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 				}
 			}
 		};
+		int err;
+		struct rtable *rt2;
+
 		security_skb_classify_flow(skb_in, &fl);
-		if (ip_route_output_key(&rt, &fl))
+		if (__ip_route_output_key(&rt, &fl))
+			goto out_unlock;
+
+		/* No need to clone since we're just using its address. */
+		rt2 = rt;
+
+		err = xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
+		switch (err) {
+		case 0:
+			if (rt != rt2)
+				goto route_done;
+			break;
+		case -EPERM:
+			rt = NULL;
+			break;
+		default:
+			goto out_unlock;
+		}
+
+		if (xfrm_decode_session_reverse(skb_in, &fl, AF_INET))
+			goto out_unlock;
+
+		if (inet_addr_type(fl.fl4_src) == RTN_LOCAL)
+			err = __ip_route_output_key(&rt2, &fl);
+		else {
+			struct flowi fl2 = {};
+			struct dst_entry *odst;
+
+			fl2.fl4_dst = fl.fl4_src;
+			if (ip_route_output_key(&rt2, &fl2))
+				goto out_unlock;
+
+			/* Ugh! */
+			odst = skb_in->dst;
+			err = ip_route_input(skb_in, fl.fl4_dst, fl.fl4_src,
+					     RT_TOS(tos), rt2->u.dst.dev);
+
+			dst_release(&rt2->u.dst);
+			rt2 = (struct rtable *)skb_in->dst;
+			skb_in->dst = odst;
+		}
+
+		if (err)
+			goto out_unlock;
+
+		err = xfrm_lookup((struct dst_entry **)&rt2, &fl, NULL,
+				  XFRM_LOOKUP_ICMP);
+		if (err == -ENOENT) {
+			if (!rt)
+				goto out_unlock;
+			goto route_done;
+		}
+
+		dst_release(&rt->u.dst);
+		rt = rt2;
+
+		if (err)
 			goto out_unlock;
 	}
 
+route_done:
 	if (!icmpv4_xrlim_allow(rt, type, code))
 		goto ende;
 
@@ -916,6 +977,22 @@ int icmp_rcv(struct sk_buff *skb)
 	struct icmphdr *icmph;
 	struct rtable *rt = (struct rtable *)skb->dst;
 
+	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb) &&
+	    skb->sp->xvec[skb->sp->len - 1]->props.flags & XFRM_STATE_ICMP) {
+		int nh;
+
+		if (!pskb_may_pull(skb, sizeof(*icmph) + sizeof(struct iphdr)))
+			goto drop;
+
+		nh = skb_network_offset(skb);
+		skb_set_network_header(skb, sizeof(*icmph));
+
+		if (!xfrm4_policy_check_reverse(NULL, XFRM_POLICY_IN, skb))
+			goto drop;
+
+		skb_set_network_header(skb, nh);
+	}
+
 	ICMP_INC_STATS_BH(ICMP_MIB_INMSGS);
 
 	switch (skb->ip_summed) {
@@ -929,8 +1006,7 @@ int icmp_rcv(struct sk_buff *skb)
 			goto error;
 	}
 
-	if (!pskb_pull(skb, sizeof(struct icmphdr)))
-		goto error;
+	__skb_pull(skb, sizeof(*icmph));
 
 	icmph = icmp_hdr(skb);