From: Tobias Brunner <tobias@strongswan.org>
Date: Fri, 25 Sep 2015 17:24:44 +0000 (+0200)
Subject: ike-natd: Create fake NAT-D payloads in a more static way
X-Git-Tag: 5.3.4dr3~20
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8484d2b01d5475abd1ded60b6b451a22cec99a61;p=thirdparty%2Fstrongswan.git

ike-natd: Create fake NAT-D payloads in a more static way

In some scenarios an IKE_SA might get restarted multiple times (e.g.
due to retransmits and delayed INVALID_KE_PAYLOAD notifies) so that
two IKE_SA_INIT messages might be sent that only differ in the
previously randomly generated NAT_DETECTION_SOURCE_IP payload.
This could cause an authentication failure on the responder if the two
peers don't use the same IKE_SA_INIT message in their InitiatorSignedOctets.

While the payload is generated in a reproducible way it will still change
when the daemon is restarted, which should make detecting the payloads
as fake a bit harder (compared to e.g. just using 0.0.0.0:0 as address).

Fixes #1131.
---

diff --git a/src/libcharon/sa/ikev2/tasks/ike_natd.c b/src/libcharon/sa/ikev2/tasks/ike_natd.c
index 9e0eb68ce9..dd34c12347 100644
--- a/src/libcharon/sa/ikev2/tasks/ike_natd.c
+++ b/src/libcharon/sa/ikev2/tasks/ike_natd.c
@@ -128,25 +128,6 @@ static chunk_t generate_natd_hash(private_ike_natd_t *this,
 	return natd_hash;
 }
 
-/**
- * build a faked NATD payload to enforce UDP encap
- */
-static chunk_t generate_natd_hash_faked(private_ike_natd_t *this)
-{
-	rng_t *rng;
-	chunk_t chunk;
-
-	rng = lib->crypto->create_rng(lib->crypto, RNG_WEAK);
-	if (!rng || !rng->allocate_bytes(rng, HASH_SIZE_SHA1, &chunk))
-	{
-		DBG1(DBG_IKE, "unable to get random bytes for NATD fake");
-		DESTROY_IF(rng);
-		return chunk_empty;
-	}
-	rng->destroy(rng);
-	return chunk;
-}
-
 /**
  * Build a NAT detection notify payload.
  */
@@ -162,7 +143,14 @@ static notify_payload_t *build_natd_payload(private_ike_natd_t *this,
 	config = this->ike_sa->get_ike_cfg(this->ike_sa);
 	if (force_encap(config) && type == NAT_DETECTION_SOURCE_IP)
 	{
-		hash = generate_natd_hash_faked(this);
+		u_int32_t addr;
+
+		/* chunk_hash() is randomly keyed so this produces a random IPv4 address
+		 * that changes with every restart but otherwise stays the same */
+		addr = chunk_hash(chunk_from_chars(0x00, 0x00, 0x00, 0x00));
+		host = host_create_from_chunk(AF_INET, chunk_from_thing(addr), 0);
+		hash = generate_natd_hash(this, ike_sa_id, host);
+		host->destroy(host);
 	}
 	else
 	{