tinc/src/protocol_key.c

/*
    protocol_key.c -- handle the meta-protocol, key exchange
    Copyright (C) 1999-2005 Ivo Timmermans,
                  2000-2014 Guus Sliepen <guus@tinc-vpn.org>

    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.

    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.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include "system.h"

#include "cipher.h"
#include "connection.h"
#include "crypto.h"
#include "logger.h"
#include "net.h"
#include "netutl.h"
#include "node.h"
#include "prf.h"
#include "protocol.h"
#include "sptps.h"
#include "utils.h"
#include "xalloc.h"

static bool mykeyused = false;

void send_key_changed(void) {
	send_request(everyone, "%d %x %s", KEY_CHANGED, rand(), myself->name);

	/* Immediately send new keys to directly connected nodes to keep UDP mappings alive */

	for list_each(connection_t, c, connection_list)
		if(c->edge && c->node && c->node->status.reachable && !c->node->status.sptps)
			send_ans_key(c->node);

	/* Force key exchange for connections using SPTPS */

	if(experimental) {
		for splay_each(node_t, n, node_tree)
			if(n->status.reachable && n->status.validkey && n->status.sptps)
				sptps_force_kex(&n->sptps);
	}
}

bool key_changed_h(connection_t *c, const char *request) {
	char name[MAX_STRING_SIZE];
	node_t *n;

	if(sscanf(request, "%*d %*x " MAX_STRING, name) != 1) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s)", "KEY_CHANGED",
			   c->name, c->hostname);
		return false;
	}

	if(seen_request(request))
		return true;

	n = lookup_node(name);

	if(!n) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) origin %s which does not exist",
			   "KEY_CHANGED", c->name, c->hostname, name);
		return true;
	}

	if(!n->status.sptps) {
		n->status.validkey = false;
		n->last_req_key = 0;
	}

	/* Tell the others */

	if(!tunnelserver)
		forward_request(c, request);

	return true;
}

static bool send_initial_sptps_data(void *handle, uint8_t type, const void *data, size_t len) {
	node_t *to = handle;
	to->sptps.send_data = send_sptps_data;
	char buf[len * 4 / 3 + 5];
	b64encode(data, buf, len);
	return send_request(to->nexthop->connection, "%d %s %s %d %s", REQ_KEY, myself->name, to->name, REQ_KEY, buf);
}

bool send_req_key(node_t *to) {
	if(to->status.sptps) {
		if(!node_read_ecdsa_public_key(to)) {
			logger(DEBUG_PROTOCOL, LOG_DEBUG, "No Ed25519 key known for %s (%s)", to->name, to->hostname);
			send_request(to->nexthop->connection, "%d %s %s %d", REQ_KEY, myself->name, to->name, REQ_PUBKEY);
			return true;
		}

		if(to->sptps.label)
			logger(DEBUG_ALWAYS, LOG_DEBUG, "send_req_key(%s) called while sptps->label != NULL!", to->name);

		char label[25 + strlen(myself->name) + strlen(to->name)];
		snprintf(label, sizeof label, "tinc UDP key expansion %s %s", myself->name, to->name);
		sptps_stop(&to->sptps);
		to->status.validkey = false;
		to->status.waitingforkey = true;
		to->last_req_key = now.tv_sec;
		to->incompression = myself->incompression;
		return sptps_start(&to->sptps, to, true, true, myself->connection->ecdsa, to->ecdsa, label, sizeof label, send_initial_sptps_data, receive_sptps_record);
	}

	return send_request(to->nexthop->connection, "%d %s %s", REQ_KEY, myself->name, to->name);
}

/* REQ_KEY is overloaded to allow arbitrary requests to be routed between two nodes. */

static bool req_key_ext_h(connection_t *c, const char *request, node_t *from, int reqno) {
	switch(reqno) {
		case REQ_PUBKEY: {
			if(!node_read_ecdsa_public_key(from)) {
				/* Request their key *before* we send our key back. Otherwise the first SPTPS packet from them will get dropped. */
				logger(DEBUG_PROTOCOL, LOG_DEBUG, "Preemptively requesting Ed25519 key for %s (%s)", from->name, from->hostname);
				send_request(from->nexthop->connection, "%d %s %s %d", REQ_KEY, myself->name, from->name, REQ_PUBKEY);
			}
			char *pubkey = ecdsa_get_base64_public_key(myself->connection->ecdsa);
			send_request(from->nexthop->connection, "%d %s %s %d %s", REQ_KEY, myself->name, from->name, ANS_PUBKEY, pubkey);
			free(pubkey);
			return true;
		}

		case ANS_PUBKEY: {
			if(node_read_ecdsa_public_key(from)) {
				logger(DEBUG_PROTOCOL, LOG_WARNING, "Got ANS_PUBKEY from %s (%s) even though we already have his pubkey", from->name, from->hostname);
				return true;
			}

			char pubkey[MAX_STRING_SIZE];
			if(sscanf(request, "%*d %*s %*s %*d " MAX_STRING, pubkey) != 1 || !(from->ecdsa = ecdsa_set_base64_public_key(pubkey))) {
				logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "ANS_PUBKEY", from->name, from->hostname, "invalid pubkey");
				return true;
			}

			logger(DEBUG_PROTOCOL, LOG_INFO, "Learned Ed25519 public key from %s (%s)", from->name, from->hostname);
			append_config_file(from->name, "Ed25519PublicKey", pubkey);
			return true;
		}

		case REQ_KEY: {
			if(!node_read_ecdsa_public_key(from)) {
				logger(DEBUG_PROTOCOL, LOG_DEBUG, "No Ed25519 key known for %s (%s)", from->name, from->hostname);
				send_request(from->nexthop->connection, "%d %s %s %d", REQ_KEY, myself->name, from->name, REQ_PUBKEY);
				return true;
			}

			if(from->sptps.label)
				logger(DEBUG_ALWAYS, LOG_DEBUG, "Got REQ_KEY from %s while we already started a SPTPS session!", from->name);

			char buf[MAX_STRING_SIZE];
			int len;

			if(sscanf(request, "%*d %*s %*s %*d " MAX_STRING, buf) != 1 || !(len = b64decode(buf, buf, strlen(buf)))) {
				logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "REQ_SPTPS_START", from->name, from->hostname, "invalid SPTPS data");
				return true;
			}

			char label[25 + strlen(from->name) + strlen(myself->name)];
			snprintf(label, sizeof label, "tinc UDP key expansion %s %s", from->name, myself->name);
			sptps_stop(&from->sptps);
			from->status.validkey = false;
			from->status.waitingforkey = true;
			from->last_req_key = now.tv_sec;
			sptps_start(&from->sptps, from, false, true, myself->connection->ecdsa, from->ecdsa, label, sizeof label, send_sptps_data, receive_sptps_record);
			sptps_receive_data(&from->sptps, buf, len);
			return true;
		}

		case REQ_SPTPS: {
			if(!from->status.validkey) {
				logger(DEBUG_PROTOCOL, LOG_ERR, "Got REQ_SPTPS from %s (%s) but we don't have a valid key yet", from->name, from->hostname);
				return true;
			}

			char buf[MAX_STRING_SIZE];
			int len;
			if(sscanf(request, "%*d %*s %*s %*d " MAX_STRING, buf) != 1 || !(len = b64decode(buf, buf, strlen(buf)))) {
				logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "REQ_SPTPS", from->name, from->hostname, "invalid SPTPS data");
				return true;
			}
			sptps_receive_data(&from->sptps, buf, len);
			return true;
		}

		default:
			logger(DEBUG_ALWAYS, LOG_ERR, "Unknown extended REQ_KEY request from %s (%s): %s", from->name, from->hostname, request);
			return true;
	}
}

bool req_key_h(connection_t *c, const char *request) {
	char from_name[MAX_STRING_SIZE];
	char to_name[MAX_STRING_SIZE];
	node_t *from, *to;
	int reqno = 0;

	if(sscanf(request, "%*d " MAX_STRING " " MAX_STRING " %d", from_name, to_name, &reqno) < 2) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s)", "REQ_KEY", c->name,
			   c->hostname);
		return false;
	}

	if(!check_id(from_name) || !check_id(to_name)) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "REQ_KEY", c->name, c->hostname, "invalid name");
		return false;
	}

	from = lookup_node(from_name);

	if(!from) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) origin %s which does not exist in our connection list",
			   "REQ_KEY", c->name, c->hostname, from_name);
		return true;
	}

	to = lookup_node(to_name);

	if(!to) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) destination %s which does not exist in our connection list",
			   "REQ_KEY", c->name, c->hostname, to_name);
		return true;
	}

	/* Check if this key request is for us */

	if(to == myself) {                      /* Yes */
		/* Is this an extended REQ_KEY message? */
		if(experimental && reqno)
			return req_key_ext_h(c, request, from, reqno);

		/* No, just send our key back */
		send_ans_key(from);
	} else {
		if(tunnelserver)
			return true;

		if(!to->status.reachable) {
			logger(DEBUG_PROTOCOL, LOG_WARNING, "Got %s from %s (%s) destination %s which is not reachable",
				"REQ_KEY", c->name, c->hostname, to_name);
			return true;
		}

		/* TODO: forwarding SPTPS packets in this way is inefficient because we send them over TCP without checking for UDP connectivity */
		send_request(to->nexthop->connection, "%s", request);
	}

	return true;
}

bool send_ans_key(node_t *to) {
	if(to->status.sptps)
		abort();

	size_t keylen = myself->incipher ? cipher_keylength(myself->incipher) : 1;
	char key[keylen * 2 + 1];

	randomize(key, keylen);

	cipher_close(to->incipher);
	digest_close(to->indigest);

	if(myself->incipher) {
		to->incipher = cipher_open_by_nid(cipher_get_nid(myself->incipher));
		if(!to->incipher)
			abort();
		if(!cipher_set_key(to->incipher, key, false))
			abort();
	}

	if(myself->indigest) {
		to->indigest = digest_open_by_nid(digest_get_nid(myself->indigest), digest_length(myself->indigest));
		if(!to->indigest)
			abort();
		if(!digest_set_key(to->indigest, key, keylen))
			abort();
	}

	to->incompression = myself->incompression;

	bin2hex(key, key, keylen);

	// Reset sequence number and late packet window
	mykeyused = true;
	to->received_seqno = 0;
	to->received = 0;
	if(replaywin) memset(to->late, 0, replaywin);

	return send_request(to->nexthop->connection, "%d %s %s %s %d %d %d %d", ANS_KEY,
						myself->name, to->name, key,
						cipher_get_nid(to->incipher),
						digest_get_nid(to->indigest),
						(int)digest_length(to->indigest),
						to->incompression);
}

bool ans_key_h(connection_t *c, const char *request) {
	char from_name[MAX_STRING_SIZE];
	char to_name[MAX_STRING_SIZE];
	char key[MAX_STRING_SIZE];
	char address[MAX_STRING_SIZE] = "";
	char port[MAX_STRING_SIZE] = "";
	int cipher, digest, maclength, compression, keylen;
	node_t *from, *to;

	if(sscanf(request, "%*d "MAX_STRING" "MAX_STRING" "MAX_STRING" %d %d %d %d "MAX_STRING" "MAX_STRING,
		from_name, to_name, key, &cipher, &digest, &maclength,
		&compression, address, port) < 7) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s)", "ANS_KEY", c->name,
			   c->hostname);
		return false;
	}

	if(!check_id(from_name) || !check_id(to_name)) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "ANS_KEY", c->name, c->hostname, "invalid name");
		return false;
	}

	from = lookup_node(from_name);

	if(!from) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) origin %s which does not exist in our connection list",
			   "ANS_KEY", c->name, c->hostname, from_name);
		return true;
	}

	to = lookup_node(to_name);

	if(!to) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) destination %s which does not exist in our connection list",
			   "ANS_KEY", c->name, c->hostname, to_name);
		return true;
	}

	/* Forward it if necessary */

	if(to != myself) {
		if(tunnelserver)
			return true;

		if(!to->status.reachable) {
			logger(DEBUG_ALWAYS, LOG_WARNING, "Got %s from %s (%s) destination %s which is not reachable",
				   "ANS_KEY", c->name, c->hostname, to_name);
			return true;
		}

		if(!*address && from->address.sa.sa_family != AF_UNSPEC) {
			char *address, *port;
			logger(DEBUG_PROTOCOL, LOG_DEBUG, "Appending reflexive UDP address to ANS_KEY from %s to %s", from->name, to->name);
			sockaddr2str(&from->address, &address, &port);
			send_request(to->nexthop->connection, "%s %s %s", request, address, port);
			free(address);
			free(port);
			return true;
		}

		return send_request(to->nexthop->connection, "%s", request);
	}

	/* Don't use key material until every check has passed. */
	cipher_close(from->outcipher);
	digest_close(from->outdigest);
	from->status.validkey = false;

	if(compression < 0 || compression > 11) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Node %s (%s) uses bogus compression level!", from->name, from->hostname);
		return true;
	}

	from->outcompression = compression;

	/* SPTPS or old-style key exchange? */

	if(from->status.sptps) {
		char buf[strlen(key)];
		int len = b64decode(key, buf, strlen(key));

		if(!len || !sptps_receive_data(&from->sptps, buf, len))
			logger(DEBUG_ALWAYS, LOG_ERR, "Error processing SPTPS data from %s (%s)", from->name, from->hostname);

		if(from->status.validkey) {
			if(*address && *port) {
				logger(DEBUG_PROTOCOL, LOG_DEBUG, "Using reflexive UDP address from %s: %s port %s", from->name, address, port);
				sockaddr_t sa = str2sockaddr(address, port);
				update_node_udp(from, &sa);
			}

			/* Don't send probes if we can't send UDP packets directly to that node.
			   TODO: the indirect (via) condition can change at any time as edges are added and removed, so this should probably be moved to graph.c. */
			if((from->via == myself || from->via == from) && from->options & OPTION_PMTU_DISCOVERY && !(from->options & OPTION_TCPONLY))
				send_mtu_probe(from);
		}

		return true;
	}

	/* Check and lookup cipher and digest algorithms */

	if(cipher) {
		if(!(from->outcipher = cipher_open_by_nid(cipher))) {
			logger(DEBUG_ALWAYS, LOG_ERR, "Node %s (%s) uses unknown cipher!", from->name, from->hostname);
			return false;
		}
	} else {
		from->outcipher = NULL;
	}

	if(digest) {
		if(!(from->outdigest = digest_open_by_nid(digest, maclength))) {
			logger(DEBUG_ALWAYS, LOG_ERR, "Node %s (%s) uses unknown digest!", from->name, from->hostname);
			return false;
		}
	} else {
		from->outdigest = NULL;
	}

	if(maclength != digest_length(from->outdigest)) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Node %s (%s) uses bogus MAC length!", from->name, from->hostname);
		return false;
	}

	/* Process key */

	keylen = hex2bin(key, key, sizeof key);

	if(keylen != (from->outcipher ? cipher_keylength(from->outcipher) : 1)) {
		logger(DEBUG_ALWAYS, LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname);
		return true;
	}

	/* Update our copy of the origin's packet key */

	if(from->outcipher && !cipher_set_key(from->outcipher, key, true))
		return false;
	if(from->outdigest && !digest_set_key(from->outdigest, key, keylen))
		return false;

	from->status.validkey = true;
	from->sent_seqno = 0;

	if(*address && *port) {
		logger(DEBUG_PROTOCOL, LOG_DEBUG, "Using reflexive UDP address from %s: %s port %s", from->name, address, port);
		sockaddr_t sa = str2sockaddr(address, port);
		update_node_udp(from, &sa);
	}

	if(from->options & OPTION_PMTU_DISCOVERY && !(from->options & OPTION_TCPONLY))
		send_mtu_probe(from);

	return true;
}