[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, 14 insertions, 3 deletions

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 2e10d46..a83b5e1 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1469,11 +1469,13 @@ restart:
 			goto dropdst;
 	}
 
+	err = -ENOENT;
+
 	if (!policy) {
 		/* To accelerate a bit...  */
 		if ((dst_orig->flags & DST_NOXFRM) ||
 		    !xfrm_policy_count[XFRM_POLICY_OUT])
-			return 0;
+			goto nopol;
 
 		policy = flow_cache_lookup(fl, dst_orig->ops->family,
 					   dir, xfrm_policy_lookup);
@@ -1483,14 +1485,18 @@ restart:
 	}
 
 	if (!policy)
-		return 0;
+		goto nopol;
 
 	family = dst_orig->ops->family;
-	policy->curlft.use_time = get_seconds();
 	pols[0] = policy;
 	npols ++;
 	xfrm_nr += pols[0]->xfrm_nr;
 
+	if ((flags & XFRM_LOOKUP_ICMP) && !(policy->flags & XFRM_POLICY_ICMP))
+		goto error;
+
+	policy->curlft.use_time = get_seconds();
+
 	switch (policy->action) {
 	default:
 	case XFRM_POLICY_BLOCK:
@@ -1649,6 +1655,11 @@ dropdst:
 	dst_release(dst_orig);
 	*dst_p = NULL;
 	return err;
+
+nopol:
+	if (flags & XFRM_LOOKUP_ICMP)
+		goto dropdst;
+	return 0;
 }
 EXPORT_SYMBOL(__xfrm_lookup);