New upstream version 5.5.2

8 files changed, 507 insertions, 18 deletions

diff --git a/src/libcharon/sa/ikev2/authenticators/pubkey_authenticator.c b/src/libcharon/sa/ikev2/authenticators/pubkey_authenticator.c
index 592f49770..19ea72d0b 100644
--- a/src/libcharon/sa/ikev2/authenticators/pubkey_authenticator.c
+++ b/src/libcharon/sa/ikev2/authenticators/pubkey_authenticator.c
@@ -217,7 +217,8 @@ static status_t sign_signature_auth(private_pubkey_authenticator_t *this,
 	}
 
 	if (keymat->get_auth_octets(keymat, FALSE, this->ike_sa_init,
-								this->nonce, id, this->reserved, &octets))
+								this->nonce, id, this->reserved, &octets,
+								schemes))
 	{
 		enumerator = array_create_enumerator(schemes);
 		while (enumerator->enumerate(enumerator, &schemep))
@@ -247,6 +248,32 @@ static status_t sign_signature_auth(private_pubkey_authenticator_t *this,
 }
 
 /**
+ * Get the auth octets and the signature scheme (in case it is changed by the
+ * keymat).
+ */
+static bool get_auth_octets_scheme(private_pubkey_authenticator_t *this,
+								   bool verify, identification_t *id,
+								   chunk_t *octets, signature_scheme_t *scheme)
+{
+	keymat_v2_t *keymat;
+	array_t *schemes;
+	bool success = FALSE;
+
+	schemes = array_create(sizeof(signature_scheme_t), 0);
+	array_insert(schemes, ARRAY_TAIL, scheme);
+
+	keymat = (keymat_v2_t*)this->ike_sa->get_keymat(this->ike_sa);
+	if (keymat->get_auth_octets(keymat, verify, this->ike_sa_init, this->nonce,
+								id, this->reserved, octets, schemes) &&
+		array_get(schemes, 0, &scheme))
+	{
+		success = TRUE;
+	}
+	array_destroy(schemes);
+	return success;
+}
+
+/**
  * Create a classic IKEv2 signature
  */
 static status_t sign_classic(private_pubkey_authenticator_t *this,
@@ -255,7 +282,6 @@ static status_t sign_classic(private_pubkey_authenticator_t *this,
 							 chunk_t *auth_data)
 {
 	signature_scheme_t scheme;
-	keymat_v2_t *keymat;
 	chunk_t octets = chunk_empty;
 	status_t status = FAILED;
 
@@ -293,9 +319,7 @@ static status_t sign_classic(private_pubkey_authenticator_t *this,
 			return FAILED;
 	}
 
-	keymat = (keymat_v2_t*)this->ike_sa->get_keymat(this->ike_sa);
-	if (keymat->get_auth_octets(keymat, FALSE, this->ike_sa_init,
-								this->nonce, id, this->reserved, &octets) &&
+	if (get_auth_octets_scheme(this, FALSE, id, &octets, &scheme) &&
 		private->sign(private, scheme, octets, auth_data))
 	{
 		status = SUCCESS;
@@ -363,7 +387,6 @@ METHOD(authenticator_t, process, status_t,
 	key_type_t key_type = KEY_ECDSA;
 	signature_scheme_t scheme;
 	status_t status = NOT_FOUND;
-	keymat_v2_t *keymat;
 	const char *reason = "unsupported";
 	bool online;
 
@@ -402,9 +425,7 @@ METHOD(authenticator_t, process, status_t,
 			return INVALID_ARG;
 	}
 	id = this->ike_sa->get_other_id(this->ike_sa);
-	keymat = (keymat_v2_t*)this->ike_sa->get_keymat(this->ike_sa);
-	if (!keymat->get_auth_octets(keymat, TRUE, this->ike_sa_init,
-								 this->nonce, id, this->reserved, &octets))
+	if (!get_auth_octets_scheme(this, TRUE, id, &octets, &scheme))
 	{
 		return FAILED;
 	}
diff --git a/src/libcharon/sa/ikev2/keymat_v2.c b/src/libcharon/sa/ikev2/keymat_v2.c
index 58efdbabe..70dacd1dc 100644
--- a/src/libcharon/sa/ikev2/keymat_v2.c
+++ b/src/libcharon/sa/ikev2/keymat_v2.c
@@ -629,7 +629,8 @@ METHOD(keymat_t, get_aead, aead_t*,
 
 METHOD(keymat_v2_t, get_auth_octets, bool,
 	private_keymat_v2_t *this, bool verify, chunk_t ike_sa_init,
-	chunk_t nonce, identification_t *id, char reserved[3], chunk_t *octets)
+	chunk_t nonce, identification_t *id, char reserved[3], chunk_t *octets,
+	array_t *schemes)
 {
 	chunk_t chunk, idx;
 	chunk_t skp;
@@ -669,7 +670,8 @@ METHOD(keymat_v2_t, get_psk_sig, bool,
 	{	/* EAP uses SK_p if no MSK has been established */
 		secret = verify ? this->skp_verify : this->skp_build;
 	}
-	if (!get_auth_octets(this, verify, ike_sa_init, nonce, id, reserved, &octets))
+	if (!get_auth_octets(this, verify, ike_sa_init, nonce, id, reserved,
+						 &octets, NULL))
 	{
 		return FALSE;
 	}
diff --git a/src/libcharon/sa/ikev2/keymat_v2.h b/src/libcharon/sa/ikev2/keymat_v2.h
index 927b62b03..36bf149fe 100644
--- a/src/libcharon/sa/ikev2/keymat_v2.h
+++ b/src/libcharon/sa/ikev2/keymat_v2.h
@@ -22,6 +22,7 @@
 #define KEYMAT_V2_H_
 
 #include <sa/keymat.h>
+#include <collections/array.h>
 
 typedef struct keymat_v2_t keymat_v2_t;
 
@@ -100,11 +101,14 @@ struct keymat_v2_t {
 	 * @param id			identity
 	 * @param reserved		reserved bytes of id_payload
 	 * @param octests		chunk receiving allocated auth octets
+	 * @param schemes		array containing signature schemes in case they
+	 * 						need to be modified by the keymat implementation
 	 * @return				TRUE if octets created successfully
 	 */
 	bool (*get_auth_octets)(keymat_v2_t *this, bool verify, chunk_t ike_sa_init,
 							chunk_t nonce, identification_t *id,
-							char reserved[3], chunk_t *octets);
+							char reserved[3], chunk_t *octets,
+							array_t *schemes);
 	/**
 	 * Build the shared secret signature used for PSK and EAP authentication.
 	 *
diff --git a/src/libcharon/sa/ikev2/task_manager_v2.c b/src/libcharon/sa/ikev2/task_manager_v2.c
index 60a262ffc..e4a16faf0 100644
--- a/src/libcharon/sa/ikev2/task_manager_v2.c
+++ b/src/libcharon/sa/ikev2/task_manager_v2.c
@@ -34,6 +34,7 @@
 #include <sa/ikev2/tasks/ike_delete.h>
 #include <sa/ikev2/tasks/ike_config.h>
 #include <sa/ikev2/tasks/ike_dpd.h>
+#include <sa/ikev2/tasks/ike_mid_sync.h>
 #include <sa/ikev2/tasks/ike_vendor.h>
 #include <sa/ikev2/tasks/ike_verify_peer_cert.h>
 #include <sa/ikev2/tasks/child_create.h>
@@ -817,7 +818,7 @@ static status_t build_response(private_task_manager_t *this, message_t *request)
 	task_t *task;
 	message_t *message;
 	host_t *me, *other;
-	bool delete = FALSE, hook = FALSE;
+	bool delete = FALSE, hook = FALSE, mid_sync = FALSE;
 	ike_sa_id_t *id = NULL;
 	uint64_t responder_spi = 0;
 	bool result;
@@ -836,6 +837,10 @@ static status_t build_response(private_task_manager_t *this, message_t *request)
 	enumerator = array_create_enumerator(this->passive_tasks);
 	while (enumerator->enumerate(enumerator, (void*)&task))
 	{
+		if (task->get_type(task) == TASK_IKE_MID_SYNC)
+		{
+			mid_sync = TRUE;
+		}
 		switch (task->build(task, message))
 		{
 			case SUCCESS:
@@ -908,6 +913,15 @@ static status_t build_response(private_task_manager_t *this, message_t *request)
 		}
 		return DESTROY_ME;
 	}
+	else if (mid_sync)
+	{
+		/* we don't want to resend messages to sync MIDs if requests with the
+		 * previous MID arrive */
+		clear_packets(this->responding.packets);
+		/* avoid increasing the expected message ID after handling a message
+		 * to sync MIDs with MID 0 */
+		return NEED_MORE;
+	}
 
 	array_compress(this->passive_tasks);
 
@@ -1069,6 +1083,10 @@ static status_t process_request(private_task_manager_t *this,
 									task = (task_t*)ike_redirect_create(
 															this->ike_sa, NULL);
 									break;
+								case IKEV2_MESSAGE_ID_SYNC:
+									task = (task_t*)ike_mid_sync_create(
+																 this->ike_sa);
+									break;
 								default:
 									break;
 							}
@@ -1200,6 +1218,12 @@ METHOD(task_manager_t, incr_mid, void,
 	}
 }
 
+METHOD(task_manager_t, get_mid, uint32_t,
+	private_task_manager_t *this, bool initiate)
+{
+	return initiate ? this->initiating.mid : this->responding.mid;
+}
+
 /**
  * Handle the given IKE fragment, if it is one.
  *
@@ -1373,6 +1397,64 @@ static status_t parse_message(private_task_manager_t *this, message_t *msg)
 	return status;
 }
 
+/**
+ * Check if a message with message ID 0 looks like it is used to synchronize
+ * the message IDs.
+ */
+static bool looks_like_mid_sync(private_task_manager_t *this, message_t *msg,
+								bool strict)
+{
+	enumerator_t *enumerator;
+	notify_payload_t *notify;
+	payload_t *payload;
+	bool found = FALSE, other = FALSE;
+
+	if (msg->get_exchange_type(msg) == INFORMATIONAL)
+	{
+		enumerator = msg->create_payload_enumerator(msg);
+		while (enumerator->enumerate(enumerator, &payload))
+		{
+			if (payload->get_type(payload) == PLV2_NOTIFY)
+			{
+				notify = (notify_payload_t*)payload;
+				switch (notify->get_notify_type(notify))
+				{
+					case IKEV2_MESSAGE_ID_SYNC:
+					case IPSEC_REPLAY_COUNTER_SYNC:
+						found = TRUE;
+						continue;
+					default:
+						break;
+				}
+			}
+			if (strict)
+			{
+				other = TRUE;
+				break;
+			}
+		}
+		enumerator->destroy(enumerator);
+	}
+	return found && !other;
+}
+
+/**
+ * Check if a message with message ID 0 looks like it is used to synchronize
+ * the message IDs and we are prepared to process it.
+ *
+ * Note: This is not called if the responder never sent a message before (i.e.
+ * we expect MID 0).
+ */
+static bool is_mid_sync(private_task_manager_t *this, message_t *msg)
+{
+	if (this->ike_sa->get_state(this->ike_sa) == IKE_ESTABLISHED &&
+		this->ike_sa->supports_extension(this->ike_sa,
+										 EXT_IKE_MESSAGE_ID_SYNC))
+	{
+		return looks_like_mid_sync(this, msg, TRUE);
+	}
+	return FALSE;
+}
 
 METHOD(task_manager_t, process_message, status_t,
 	private_task_manager_t *this, message_t *msg)
@@ -1421,7 +1503,7 @@ METHOD(task_manager_t, process_message, status_t,
 	mid = msg->get_message_id(msg);
 	if (msg->get_request(msg))
 	{
-		if (mid == this->responding.mid)
+		if (mid == this->responding.mid || (mid == 0 && is_mid_sync(this, msg)))
 		{
 			/* reject initial messages if not received in specific states,
 			 * after rekeying we only expect a DELETE in an INFORMATIONAL */
@@ -1462,7 +1544,8 @@ METHOD(task_manager_t, process_message, status_t,
 			}
 		}
 		else if ((mid == this->responding.mid - 1) &&
-				 array_count(this->responding.packets))
+				 array_count(this->responding.packets) &&
+				 !(mid == 0 && looks_like_mid_sync(this, msg, FALSE)))
 		{
 			status = handle_fragment(this, &this->responding.defrag, msg);
 			if (status != SUCCESS)
@@ -1477,7 +1560,7 @@ METHOD(task_manager_t, process_message, status_t,
 		}
 		else
 		{
-			DBG1(DBG_IKE, "received message ID %d, expected %d. Ignored",
+			DBG1(DBG_IKE, "received message ID %d, expected %d, ignored",
 				 mid, this->responding.mid);
 		}
 	}
@@ -1515,7 +1598,7 @@ METHOD(task_manager_t, process_message, status_t,
 		}
 		else
 		{
-			DBG1(DBG_IKE, "received message ID %d, expected %d. Ignored",
+			DBG1(DBG_IKE, "received message ID %d, expected %d, ignored",
 				 mid, this->initiating.mid);
 			return SUCCESS;
 		}
@@ -2046,6 +2129,7 @@ task_manager_v2_t *task_manager_v2_create(ike_sa_t *ike_sa)
 				.initiate = _initiate,
 				.retransmit = _retransmit,
 				.incr_mid = _incr_mid,
+				.get_mid = _get_mid,
 				.reset = _reset,
 				.adopt_tasks = _adopt_tasks,
 				.adopt_child_tasks = _adopt_child_tasks,
diff --git a/src/libcharon/sa/ikev2/tasks/ike_auth.c b/src/libcharon/sa/ikev2/tasks/ike_auth.c
index 036910d0e..53daaf2ad 100644
--- a/src/libcharon/sa/ikev2/tasks/ike_auth.c
+++ b/src/libcharon/sa/ikev2/tasks/ike_auth.c
@@ -417,6 +417,9 @@ METHOD(task_t, build_i, status_t,
 		/* indicate support for EAP-only authentication */
 		message->add_notify(message, FALSE, EAP_ONLY_AUTHENTICATION,
 							chunk_empty);
+		/* indicate support for RFC 6311 Message ID synchronization */
+		message->add_notify(message, FALSE, IKEV2_MESSAGE_ID_SYNC_SUPPORTED,
+							chunk_empty);
 	}
 
 	if (!this->do_another_auth && !this->my_auth)
@@ -466,7 +469,8 @@ METHOD(task_t, build_i, status_t,
 		get_reserved_id_bytes(this, id_payload);
 		message->add_payload(message, (payload_t*)id_payload);
 
-		if (idr && message->get_message_id(message) == 1 &&
+		if (idr && !idr->contains_wildcards(idr) &&
+			message->get_message_id(message) == 1 &&
 			this->peer_cfg->get_unique_policy(this->peer_cfg) != UNIQUE_NO &&
 			this->peer_cfg->get_unique_policy(this->peer_cfg) != UNIQUE_NEVER)
 		{
@@ -991,6 +995,10 @@ METHOD(task_t, process_i, status_t,
 						DBG1(DBG_IKE, "received invalid REDIRECT notify");
 					}
 					break;
+				case IKEV2_MESSAGE_ID_SYNC_SUPPORTED:
+					this->ike_sa->enable_extension(this->ike_sa,
+												   EXT_IKE_MESSAGE_ID_SYNC);
+					break;
 				default:
 				{
 					if (type <= 16383)
diff --git a/src/libcharon/sa/ikev2/tasks/ike_init.c b/src/libcharon/sa/ikev2/tasks/ike_init.c
index d82e206b8..58b710616 100644
--- a/src/libcharon/sa/ikev2/tasks/ike_init.c
+++ b/src/libcharon/sa/ikev2/tasks/ike_init.c
@@ -159,6 +159,10 @@ static void send_supported_hash_algorithms(private_ike_init_t *this,
 	auth_cfg_t *auth;
 	auth_rule_t rule;
 	uintptr_t config;
+	int written;
+	size_t len = BUF_LEN;
+	char buf[len];
+	char *pos = buf;
 	char *plugin_name;
 
 	algos = hash_algorithm_set_create();
@@ -205,11 +209,23 @@ static void send_supported_hash_algorithms(private_ike_init_t *this,
 		while (enumerator->enumerate(enumerator, &hash))
 		{
 			writer->write_uint16(writer, hash);
+
+			/* generate debug output */
+			written = snprintf(pos, len, " %N", hash_algorithm_short_names,
+							   hash);
+			if (written > 0 && written < len)
+			{
+				pos += written;
+				len -= written;
+			}
 		}
 		enumerator->destroy(enumerator);
 		message->add_notify(message, FALSE, SIGNATURE_HASH_ALGORITHMS,
 							writer->get_buf(writer));
 		writer->destroy(writer);
+
+		*pos = '\0';
+		DBG2(DBG_CFG, "sending supported signature hash algorithms:%s", buf);
 	}
 	algos->destroy(algos);
 }
@@ -222,6 +238,10 @@ static void handle_supported_hash_algorithms(private_ike_init_t *this,
 {
 	bio_reader_t *reader;
 	uint16_t algo;
+	int written;
+	size_t len = BUF_LEN;
+	char buf[len];
+	char *pos = buf;
 	bool added = FALSE;
 
 	reader = bio_reader_create(notify->get_notification_data(notify));
@@ -231,10 +251,22 @@ static void handle_supported_hash_algorithms(private_ike_init_t *this,
 		{
 			this->keymat->add_hash_algorithm(this->keymat, algo);
 			added = TRUE;
+
+			/* generate debug output */
+			written = snprintf(pos, len, " %N", hash_algorithm_short_names,
+							   algo);
+			if (written > 0 && written < len)
+			{
+				pos += written;
+				len -= written;
+			}
 		}
 	}
 	reader->destroy(reader);
 
+	*pos = '\0';
+	DBG2(DBG_CFG, "received supported signature hash algorithms:%s", buf);
+
 	if (added)
 	{
 		this->ike_sa->enable_extension(this->ike_sa, EXT_SIGNATURE_AUTH);
diff --git a/src/libcharon/sa/ikev2/tasks/ike_mid_sync.c b/src/libcharon/sa/ikev2/tasks/ike_mid_sync.c
new file mode 100644
index 000000000..24cf276f4
--- /dev/null
+++ b/src/libcharon/sa/ikev2/tasks/ike_mid_sync.c
@@ -0,0 +1,264 @@
+/*
+ * Copyright (C) 2016 Tobias Brunner
+ * HSR Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+/*
+ * Copyright (C) 2016 Stephen J. Bevan
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "ike_mid_sync.h"
+
+#include <daemon.h>
+#include <bio/bio_reader.h>
+#include <bio/bio_writer.h>
+#include <encoding/payloads/notify_payload.h>
+
+typedef struct private_ike_mid_sync_t private_ike_mid_sync_t;
+
+/**
+ * Private members
+ */
+struct private_ike_mid_sync_t {
+
+	/**
+	 * Public methods and task_t interface.
+	 */
+	ike_mid_sync_t public;
+
+	/**
+	 * Assigned IKE_SA.
+	 */
+	ike_sa_t *ike_sa;
+
+	/**
+	 * Nonce sent by the peer and expected to be returned
+	 */
+	chunk_t nonce;
+
+	/**
+	 * Expected next sender message ID
+	 */
+	uint32_t send;
+
+	/**
+	 * Expected received message ID
+	 */
+	uint32_t recv;
+};
+
+/*
+ * Encoding of IKEV2_MESSAGE_SYNC_ID notify, RFC 6311
+ *
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * | Next Payload  |C|  RESERVED   |         Payload Length        |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |Protocol ID(=0)| SPI Size (=0) |      Notify Message Type      |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |             Nonce Data                                        |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |             EXPECTED_SEND_REQ_MESSAGE_ID                      |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |             EXPECTED_RECV_REQ_MESSAGE_ID                      |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ */
+
+/*
+ * RFC 6311 section 5.1
+ *
+ *  o  The peer MUST silently drop any received synchronization message
+ *     if M1 is lower than or equal to the highest value it has seen from
+ *     the cluster.  This includes any previous received synchronization
+ *     messages.
+ */
+METHOD(task_t, pre_process, status_t,
+	private_ike_mid_sync_t *this, message_t *message)
+{
+	notify_payload_t *notify;
+	bio_reader_t *reader;
+	chunk_t nonce;
+	uint32_t resp;
+
+	if (message->get_message_id(message) != 0)
+	{	/* ignore the notify if it was contained in an INFORMATIONAL with
+		 * unexpected message ID */
+		return SUCCESS;
+	}
+	if (!this->ike_sa->supports_extension(this->ike_sa,
+										  EXT_IKE_MESSAGE_ID_SYNC))
+	{
+		DBG1(DBG_ENC, "unexpected %N notify, ignored", notify_type_names,
+			 IKEV2_MESSAGE_ID_SYNC);
+		return FAILED;
+	}
+	notify = message->get_notify(message, IKEV2_MESSAGE_ID_SYNC);
+
+	reader = bio_reader_create(notify->get_notification_data(notify));
+	if (!reader->read_data(reader, 4, &nonce) ||
+		!reader->read_uint32(reader, &this->send) ||
+		!reader->read_uint32(reader, &this->recv))
+	{
+		reader->destroy(reader);
+		DBG1(DBG_ENC, "received invalid %N notify",
+			 notify_type_names, IKEV2_MESSAGE_ID_SYNC);
+		return FAILED;
+	}
+	reader->destroy(reader);
+	resp = this->ike_sa->get_message_id(this->ike_sa, FALSE);
+	if (this->send < resp)
+	{
+		DBG1(DBG_ENC, "ignore %N notify with lower (%d) than expected (%d) "
+			 "sender MID", notify_type_names, IKEV2_MESSAGE_ID_SYNC, this->send,
+			 resp);
+		return FAILED;
+	}
+	this->nonce = chunk_clone(nonce);
+	return SUCCESS;
+}
+
+/**
+ * Check if there are any active tasks, indicating that we already
+ * used the currents message ID and are waiting for a response.
+ */
+static bool has_active_tasks(private_ike_mid_sync_t *this)
+{
+	enumerator_t *enumerator;
+	task_t *task;
+	bool active;
+
+	enumerator = this->ike_sa->create_task_enumerator(this->ike_sa,
+													  TASK_QUEUE_ACTIVE);
+	active = enumerator->enumerate(enumerator, &task);
+	enumerator->destroy(enumerator);
+	return active;
+}
+
+/*
+ * RFC 6311 section 5.1
+ *
+ *  o  M2 MUST be at least the higher of the received M1, and one more
+ *     than the highest sender value received from the cluster.  This
+ *     includes any previous received synchronization messages.
+ *
+ *  o  P2 MUST be the higher of the received P1 value, and one more than
+ *     the highest sender value used by the peer.
+ *
+ * M1 is this->send, P1 is this->recv
+ */
+METHOD(task_t, process, status_t,
+	private_ike_mid_sync_t *this, message_t *message)
+{
+	uint32_t resp, init, m2, p2;
+
+	if (message->get_message_id(message) != 0)
+	{	/* ignore the notify if it was contained in an INFORMATIONAL with
+		 * unexpected message id */
+		return SUCCESS;
+	}
+	resp = this->ike_sa->get_message_id(this->ike_sa, FALSE);
+	m2 = max(this->send, resp);
+	if (resp != m2)
+	{
+		this->ike_sa->set_message_id(this->ike_sa, FALSE, m2);
+	}
+	init = this->ike_sa->get_message_id(this->ike_sa, TRUE);
+	p2 = max(this->recv, has_active_tasks(this) ? init + 1 : init);
+	if (init != p2)
+	{
+		this->ike_sa->set_message_id(this->ike_sa, TRUE, p2);
+	}
+	DBG1(DBG_IKE, "responder requested MID sync: initiating %d[%d], "
+		 "responding %d[%d]", p2, init, m2, resp);
+	this->send = p2;
+	this->recv = m2;
+	return NEED_MORE;
+}
+
+METHOD(task_t, build, status_t,
+	private_ike_mid_sync_t *this, message_t *message)
+{
+	bio_writer_t *writer;
+
+	writer = bio_writer_create(12);
+	writer->write_data(writer, this->nonce);
+	writer->write_uint32(writer, this->send);
+	writer->write_uint32(writer, this->recv);
+
+	message->set_message_id(message, 0);
+	message->add_notify(message, FALSE, IKEV2_MESSAGE_ID_SYNC,
+						writer->get_buf(writer));
+
+	writer->destroy(writer);
+	return SUCCESS;
+}
+
+METHOD(task_t, get_type, task_type_t,
+	private_ike_mid_sync_t *this)
+{
+	return TASK_IKE_MID_SYNC;
+}
+
+METHOD(task_t, migrate, void,
+	private_ike_mid_sync_t *this, ike_sa_t *ike_sa)
+{
+	this->ike_sa = ike_sa;
+	chunk_free(&this->nonce);
+}
+
+METHOD(task_t, destroy, void,
+	private_ike_mid_sync_t *this)
+{
+	chunk_free(&this->nonce);
+	free(this);
+}
+
+/*
+ * Described in header.
+ */
+ike_mid_sync_t *ike_mid_sync_create(ike_sa_t *ike_sa)
+{
+	private_ike_mid_sync_t *this;
+
+	INIT(this,
+		.public = {
+			.task = {
+				.get_type = _get_type,
+				.build = _build,
+				.pre_process = _pre_process,
+				.process = _process,
+				.migrate = _migrate,
+				.destroy = _destroy,
+			},
+		},
+		.ike_sa = ike_sa,
+	);
+	return &this->public;
+}
diff --git a/src/libcharon/sa/ikev2/tasks/ike_mid_sync.h b/src/libcharon/sa/ikev2/tasks/ike_mid_sync.h
new file mode 100644
index 000000000..9dd46f925
--- /dev/null
+++ b/src/libcharon/sa/ikev2/tasks/ike_mid_sync.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2016 Tobias Brunner
+ * HSR Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+/*
+ * Copyright (C) 2016 Stephen J. Bevan
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * @defgroup ike_mid_sync ike_mid_sync
+ * @{ @ingroup tasks_v2
+ */
+
+#ifndef IKE_MID_SYNC_H_
+#define IKE_MID_SYNC_H_
+
+typedef struct ike_mid_sync_t ike_mid_sync_t;
+
+#include <library.h>
+#include <sa/ike_sa.h>
+#include <sa/task.h>
+
+/**
+ * Task of type TASK_IKE_MID_SYNC, implements RFC 6311 responder.
+ *
+ * This task handles an IKEV2_MESSAGE_ID_SYNC notify sent by a peer
+ * and if acceptable updates the SA MIDs and replies with the updated
+ * MID values.
+ */
+struct ike_mid_sync_t {
+
+	/**
+	 * Implements the task_t interface
+	 */
+	task_t task;
+};
+
+/**
+ * Create a new TASK_IKE_MID_SYNC task.
+ *
+ * @param ike_sa	IKE_SA this task works for
+ * @return			task to handle by the task_manager
+ */
+ike_mid_sync_t *ike_mid_sync_create(ike_sa_t *ike_sa);
+
+#endif /** IKE_MID_SYNC_H_ @}*/