src/ap/comeback_token.c

/*
 * hostapd / Comeback token mechanism for SAE
 * Copyright (c) 2002-2017, Jouni Malinen <j@w1.fi>
 *
 * This software may be distributed under the terms of the BSD license.
 * See README for more details.
 */

#include "utils/includes.h"

#include "utils/common.h"
#include "hostapd.h"
#include "crypto/sha256.h"
#include "crypto/random.h"
#include "common/ieee802_11_defs.h"
#include "comeback_token.h"


#if defined(CONFIG_SAE) || defined(CONFIG_PASN)

static int comeback_token_hash(const u8 *comeback_key, const u8 *addr, u8 *idx)
{
	u8 hash[SHA256_MAC_LEN];

	if (hmac_sha256(comeback_key, COMEBACK_KEY_SIZE,
			addr, ETH_ALEN, hash) < 0)
		return -1;
	*idx = hash[0];
	return 0;
}


int check_comeback_token(const u8 *comeback_key,
			 u16 *comeback_pending_idx, const u8 *addr,
			 const u8 *token, size_t token_len)
{
	u8 mac[SHA256_MAC_LEN];
	const u8 *addrs[2];
	size_t len[2];
	u16 token_idx;
	u8 idx;

	if (token_len != SHA256_MAC_LEN ||
	    comeback_token_hash(comeback_key, addr, &idx) < 0)
		return -1;
	token_idx = comeback_pending_idx[idx];
	if (token_idx == 0 || token_idx != WPA_GET_BE16(token)) {
		wpa_printf(MSG_DEBUG,
			   "Comeback: Invalid anti-clogging token from "
			   MACSTR " - token_idx 0x%04x, expected 0x%04x",
			   MAC2STR(addr), WPA_GET_BE16(token), token_idx);
		return -1;
	}

	addrs[0] = addr;
	len[0] = ETH_ALEN;
	addrs[1] = token;
	len[1] = 2;
	if (hmac_sha256_vector(comeback_key, COMEBACK_KEY_SIZE,
			       2, addrs, len, mac) < 0 ||
	    os_memcmp_const(token + 2, &mac[2], SHA256_MAC_LEN - 2) != 0)
		return -1;

	comeback_pending_idx[idx] = 0; /* invalidate used token */

	return 0;
}


struct wpabuf *
auth_build_token_req(struct os_reltime *last_comeback_key_update,
		     u8 *comeback_key, u16 comeback_idx,
		     u16 *comeback_pending_idx, size_t idx_len,
		     int group, const u8 *addr, int h2e)
{
	struct wpabuf *buf;
	u8 *token;
	struct os_reltime now;
	u8 idx[2];
	const u8 *addrs[2];
	size_t len[2];
	u8 p_idx;
	u16 token_idx;

	os_get_reltime(&now);
	if (!os_reltime_initialized(last_comeback_key_update) ||
	    os_reltime_expired(&now, last_comeback_key_update, 60) ||
	    comeback_idx == 0xffff) {
		if (random_get_bytes(comeback_key, COMEBACK_KEY_SIZE) < 0)
			return NULL;
		wpa_hexdump(MSG_DEBUG, "Comeback: Updated token key",
			    comeback_key, COMEBACK_KEY_SIZE);
		*last_comeback_key_update = now;
		comeback_idx = 0;
		os_memset(comeback_pending_idx, 0, idx_len);
	}

	buf = wpabuf_alloc(sizeof(le16) + 3 + SHA256_MAC_LEN);
	if (buf == NULL)
		return NULL;

	if (group)
		wpabuf_put_le16(buf, group); /* Finite Cyclic Group */

	if (h2e) {
		/* Encapsulate Anti-clogging Token field in a container IE */
		wpabuf_put_u8(buf, WLAN_EID_EXTENSION);
		wpabuf_put_u8(buf, 1 + SHA256_MAC_LEN);
		wpabuf_put_u8(buf, WLAN_EID_EXT_ANTI_CLOGGING_TOKEN);
	}

	if (comeback_token_hash(comeback_key, addr, &p_idx) < 0) {
		wpabuf_free(buf);
		return NULL;
	}

	token_idx = comeback_pending_idx[p_idx];
	if (!token_idx) {
		comeback_idx++;
		token_idx = comeback_idx;
		comeback_pending_idx[p_idx] = token_idx;
	}
	WPA_PUT_BE16(idx, token_idx);
	token = wpabuf_put(buf, SHA256_MAC_LEN);
	addrs[0] = addr;
	len[0] = ETH_ALEN;
	addrs[1] = idx;
	len[1] = sizeof(idx);
	if (hmac_sha256_vector(comeback_key, COMEBACK_KEY_SIZE,
			       2, addrs, len, token) < 0) {
		wpabuf_free(buf);
		return NULL;
	}
	WPA_PUT_BE16(token, token_idx);

	return buf;
}

#endif /* defined(CONFIG_SAE) || defined(CONFIG_PASN) */