iwd/src/eap-tls.c

/*
 *
 *  Wireless daemon for Linux
 *
 *  Copyright (C) 2013-2014  Intel Corporation. All rights reserved.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <ell/ell.h>
#include <ell/tls-private.h>

#include "eap.h"

struct eap_tls_state {
	char *ca_cert;
	char *client_cert;
	char *client_key;
	char *passphrase;

	struct l_tls *tls;
	uint8_t *rx_pkt_buf;
	size_t rx_pkt_received, rx_pkt_len;
	uint8_t *tx_pkt_buf;
	size_t tx_pkt_len, tx_pkt_capacity, tx_pkt_offset;
	bool completed;
};

static int eap_tls_probe(struct eap_state *eap, const char *name)
{
	struct eap_tls_state *tls;

	if (strcasecmp(name, "TLS"))
		return -ENOTSUP;

	tls = l_new(struct eap_tls_state, 1);

	eap_set_data(eap, tls);

	return 0;
}

static void eap_tls_remove(struct eap_state *eap)
{
	struct eap_tls_state *tls = eap_get_data(eap);

	eap_set_data(eap, NULL);

	l_free(tls->ca_cert);
	l_free(tls->client_cert);
	l_free(tls->client_key);
	l_free(tls->passphrase);

	if (tls->rx_pkt_buf) {
		l_free(tls->rx_pkt_buf);
		tls->rx_pkt_buf = NULL;
	}

	if (tls->tx_pkt_buf) {
		l_free(tls->tx_pkt_buf);
		tls->tx_pkt_buf = NULL;
		tls->tx_pkt_capacity = 0;
		tls->tx_pkt_len = 0;
	}

	if (tls->tls) {
		l_tls_free(tls->tls);
		tls->tls = NULL;
	}

	l_free(tls);
}

#define EAP_TLS_RESPONSE_HEADER_LEN	10

#define EAP_TLS_FLAG_L (1 << 7)
#define EAP_TLS_FLAG_M (1 << 6)
#define EAP_TLS_FLAG_S (1 << 5)

static uint8_t *eap_tls_tx_buf_reserve(struct eap_tls_state *tls, size_t size)
{
	int offset = tls->tx_pkt_offset + tls->tx_pkt_len;
	size_t end_offset = offset + size;

	tls->tx_pkt_len += size;

	if (end_offset > tls->tx_pkt_capacity) {
		tls->tx_pkt_capacity = end_offset + 1024;
		tls->tx_pkt_buf =
			l_realloc(tls->tx_pkt_buf, tls->tx_pkt_capacity);
	}

	return tls->tx_pkt_buf + offset;
}

static void eap_tls_tx_cb(const uint8_t *data, size_t len, void *user_data)
{
	struct eap_state *eap = user_data;
	struct eap_tls_state *tls = eap_get_data(eap);

	memcpy(eap_tls_tx_buf_reserve(tls, len), data, len);
}

static void eap_tls_data_cb(const uint8_t *data, size_t len, void *user_data)
{
	/* This should never be called */
}

static void eap_tls_ready_cb(const char *peer_identity, void *user_data)
{
	struct eap_state *eap = user_data;
	struct eap_tls_state *tls = eap_get_data(eap);
	uint8_t msk_emsk[128];
	uint8_t iv[64];
	uint8_t seed[64];

	/* TODO: if we have a CA certificate require non-NULL peer_identity */

	eap_method_success(eap);
	tls->completed = true;

	eap_start_complete_timeout(eap);

	/* MSK, EMSK and IV derivation */
	memcpy(seed +  0, tls->tls->pending.client_random, 32);
	memcpy(seed + 32, tls->tls->pending.server_random, 32);

	tls_prf_get_bytes(tls->tls, L_CHECKSUM_SHA256, 32,
				tls->tls->pending.master_secret,
				sizeof(tls->tls->pending.master_secret),
				"client EAP encryption", seed, 64,
				msk_emsk, 128);
	tls_prf_get_bytes(tls->tls, L_CHECKSUM_SHA256, 32, NULL, 0,
				"client EAP encryption", seed, 64,
				iv, 64);

	memset(seed, 0, 64);

	eap_set_key_material(eap, msk_emsk + 0, 64, msk_emsk + 64, 64, iv, 64);
}

static void eap_tls_disconnect_cb(enum l_tls_alert_desc reason,
					bool remote, void *user_data)
{
	struct eap_state *eap = user_data;
	struct eap_tls_state *tls = eap_get_data(eap);

	tls->completed = true;
}

static void eap_tls_handle_request(struct eap_state *eap,
					const uint8_t *pkt, size_t len)
{
	uint8_t flags;
	uint32_t total_len;
	struct eap_tls_state *tls = eap_get_data(eap);
	size_t fragment_len;
	uint8_t *tx_buf;

	if (len < 1) {
		l_error("EAP-TLS request too short");
		goto err;
	}

	flags = pkt[0];

	pkt += 1;
	len -= 1;

	/* Check if we're expecting a fragment ACK */
	if (tls->tx_pkt_len) {
		if (flags || len) {
			l_error("EAP-TLS request is not an ACK");
			goto err;
		}

		/* Send next response fragment, prepend the 6-byte header */
		tx_buf = &tls->tx_pkt_buf[tls->tx_pkt_offset - 6];

		fragment_len = eap_get_mtu(eap) - 6;
		tx_buf[5] = EAP_TLS_FLAG_M; /* Flags */

		if (tls->tx_pkt_len <= fragment_len) {
			fragment_len = tls->tx_pkt_len;
			tx_buf[5] = 0; /* Flags */
		}

		eap_send_response(eap, EAP_TYPE_TLS_EAP,
					tx_buf, fragment_len + 6);

		tls->tx_pkt_len -= fragment_len;
		tls->tx_pkt_offset += fragment_len;

		return;
	}

	/* Complain if S bit is not correct */
	if (!(flags & EAP_TLS_FLAG_S) == !tls->tls) {
		l_error("EAP-TLS request S flag invalid");
		goto err;
	}

	/* Method can't be restarted */
	if ((flags & EAP_TLS_FLAG_S) && tls->completed) {
		l_error("EAP-TLS start after completed");
		goto err;
	}

	if (flags & EAP_TLS_FLAG_L) {
		if (len < 7) {
			l_error("EAP-TLS request with L flag too short");
			goto err;
		}

		total_len = l_get_be32(pkt);
		pkt += 4;
		len -= 4;

		if (tls->rx_pkt_buf && total_len != tls->rx_pkt_len) {
			l_error("EAP-TLS request length mismatch");

			l_free(tls->rx_pkt_buf);
			tls->rx_pkt_buf = NULL;

			goto err;
		}
	}

	if (!tls->rx_pkt_buf && (flags & EAP_TLS_FLAG_M)) {
		if (!(flags & EAP_TLS_FLAG_L)) {
			l_error("EAP-TLS requst 1st fragment with no length");

			goto err;
		}

		tls->rx_pkt_buf = l_malloc(total_len);
		tls->rx_pkt_len = total_len;
		tls->rx_pkt_received = 0;
	}

	if (tls->rx_pkt_buf) {
		if (
				((flags & EAP_TLS_FLAG_M) &&
				 tls->rx_pkt_received + len >=
				 tls->rx_pkt_len) ||
				(!(flags & EAP_TLS_FLAG_M) &&
				 tls->rx_pkt_received + len !=
				 tls->rx_pkt_len)) {
			l_error("EAP-TLS request fragment length mismatch");

			l_free(tls->rx_pkt_buf);
			tls->rx_pkt_buf = NULL;

			goto err;
		}

		memcpy(tls->rx_pkt_buf + tls->rx_pkt_received, pkt, len);
		tls->rx_pkt_received += len;
	}

	if (flags & EAP_TLS_FLAG_M) {
		uint8_t buf[6];

		/* Send an empty response as ACK */
		buf[5] = 0;
		eap_send_response(eap, EAP_TYPE_TLS_EAP, buf, 6);

		return;
	}

	if (tls->rx_pkt_buf) {
		pkt = tls->rx_pkt_buf;
		len = tls->rx_pkt_len;
	}

	eap_tls_tx_buf_reserve(tls, EAP_TLS_RESPONSE_HEADER_LEN);
	tls->tx_pkt_offset = tls->tx_pkt_len;
	tls->tx_pkt_len = 0;

	if (flags & EAP_TLS_FLAG_S) {
		tls->tls = l_tls_new(false, eap_tls_data_cb,
					eap_tls_tx_cb, eap_tls_ready_cb,
					eap_tls_disconnect_cb, eap);

		if (!tls->tls) {
			l_error("Creating a TLS instance failed");
			goto err;
		}

		l_tls_set_auth_data(tls->tls, tls->client_cert, tls->client_key,
					tls->passphrase);

		if (tls->ca_cert)
			l_tls_set_cacert(tls->tls, tls->ca_cert);
	}

	/*
	 * Here we take advantage of knowing that ell will send all the
	 * records corresponding to the current handshake step from within
	 * the l_tls_handle_rx call because it doesn't use any other context
	 * such as timers - basic TLS specifies no timeouts.  Otherwise we
	 * would need to analyze the record types in eap_tls_tx_cb to decide
	 * when we're ready to send out a response.
	 */
	if (len)
		l_tls_handle_rx(tls->tls, pkt, len);

	if (tls->rx_pkt_buf) {
		l_free(tls->rx_pkt_buf);
		tls->rx_pkt_buf = NULL;
	}

	/*
	 * Note if tls->completed && !eap->method_success we can send an empty
	 * response instead of passing the TLS alert.
	 */

	if (tls->tx_pkt_len + 6 <= eap_get_mtu(eap)) {
		/*
		 * Response fits in a single response packet, prepend the
		 * 6-byte header (no length) before the data.
		 */
		tx_buf = &tls->tx_pkt_buf[tls->tx_pkt_offset - 6];

		tx_buf[5] = 0; /* Flags */

		eap_send_response(eap, EAP_TYPE_TLS_EAP,
					tx_buf, tls->tx_pkt_len + 6);

		tls->tx_pkt_len = 0;
	} else {
		/*
		 * Fragmentation needed, prepend the 10-byte header
		 * (4 EAP header + 2 response + 4 length) to build the
		 * initial fragment packet.
		 */
		tx_buf = &tls->tx_pkt_buf[tls->tx_pkt_offset - 10];

		tx_buf[5] = EAP_TLS_FLAG_L | EAP_TLS_FLAG_M; /* Flags */
		l_put_be32(tls->tx_pkt_len, &tx_buf[6]);

		fragment_len = eap_get_mtu(eap) - 10;
		eap_send_response(eap, EAP_TYPE_TLS_EAP,
					tx_buf, fragment_len + 10);

		tls->tx_pkt_len -= fragment_len;
		tls->tx_pkt_offset += fragment_len;
	}

	if (tls->completed) {
		l_tls_free(tls->tls);
		tls->tls = NULL;
	}

	return;

err:
	tls->completed = true;

	l_tls_free(tls->tls);
	tls->tls = NULL;

	eap_method_error(eap);
}

static bool eap_tls_load_settings(struct eap_state *eap,
					struct l_settings *settings,
					const char *prefix)
{
	struct eap_tls_state *tls = eap_get_data(eap);
	char setting[64];

	snprintf(setting, sizeof(setting), "%sTLS-CACert", prefix);
	tls->ca_cert = l_strdup(l_settings_get_value(settings,
						"Security", setting));

	snprintf(setting, sizeof(setting), "%sTLS-ClientCert", prefix);
	tls->client_cert = l_strdup(l_settings_get_value(settings,
						"Security", setting));

	snprintf(setting, sizeof(setting), "%sTLS-ClientKey", prefix);
	tls->client_key = l_strdup(l_settings_get_value(settings,
						"Security", setting));

	snprintf(setting, sizeof(setting), "%sTLS-ClientKeyPassphrase", prefix);
	tls->passphrase = l_strdup(l_settings_get_value(settings,
						"Security", setting));

	if (!tls->client_cert && tls->client_key) {
		l_error("Client key present but no client certificate");
		return false;
	}

	if (!tls->client_key && tls->passphrase) {
		l_error("Passphrase present but no client private key");
		return false;
	}

	return true;
}

static struct eap_method eap_tls = {
	.request_type = EAP_TYPE_TLS_EAP,
	.exports_msk = true,
	.name = "TLS",

	.probe = eap_tls_probe,
	.remove = eap_tls_remove,
	.handle_request = eap_tls_handle_request,
	.load_settings = eap_tls_load_settings,
};

static int eap_tls_init(void)
{
	l_debug("");
	return eap_register_method(&eap_tls);
}

static void eap_tls_exit(void)
{
	l_debug("");
	eap_unregister_method(&eap_tls);
}

EAP_METHOD_BUILTIN(eap_tls, eap_tls_init, eap_tls_exit)