src/drivers/scan_helpers.c

/*
 * WPA Supplicant - Helper functions for scan result processing
 * Copyright (c) 2007, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */

#include "includes.h"

#include "common.h"
#include "drivers/driver.h"
#include "ieee802_11_defs.h"


const u8 * wpa_scan_get_ie(const struct wpa_scan_res *res, u8 ie)
{
	const u8 *end, *pos;

	pos = (const u8 *) (res + 1);
	end = pos + res->ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == ie)
			return pos;
		pos += 2 + pos[1];
	}

	return NULL;
}


const u8 * wpa_scan_get_vendor_ie(const struct wpa_scan_res *res,
				  u32 vendor_type)
{
	const u8 *end, *pos;

	pos = (const u8 *) (res + 1);
	end = pos + res->ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == WLAN_EID_VENDOR_SPECIFIC && pos[1] >= 4 &&
		    vendor_type == WPA_GET_BE32(&pos[2]))
			return pos;
		pos += 2 + pos[1];
	}

	return NULL;
}


int wpa_scan_get_max_rate(const struct wpa_scan_res *res)
{
	int rate = 0;
	const u8 *ie;
	int i;

	ie = wpa_scan_get_ie(res, WLAN_EID_SUPP_RATES);
	for (i = 0; ie && i < ie[1]; i++) {
		if ((ie[i + 2] & 0x7f) > rate)
			rate = ie[i + 2] & 0x7f;
	}

	ie = wpa_scan_get_ie(res, WLAN_EID_EXT_SUPP_RATES);
	for (i = 0; ie && i < ie[1]; i++) {
		if ((ie[i + 2] & 0x7f) > rate)
			rate = ie[i + 2] & 0x7f;
	}

	return rate;
}


void wpa_scan_results_free(struct wpa_scan_results *res)
{
	size_t i;

	if (res == NULL)
		return;

	for (i = 0; i < res->num; i++)
		os_free(res->res[i]);
	os_free(res->res);
	os_free(res);
}


/* Compare function for sorting scan results. Return >0 if @b is considered
 * better. */
static int wpa_scan_result_compar(const void *a, const void *b)
{
	struct wpa_scan_res **_wa = (void *) a;
	struct wpa_scan_res **_wb = (void *) b;
	struct wpa_scan_res *wa = *_wa;
	struct wpa_scan_res *wb = *_wb;
	int wpa_a, wpa_b, maxrate_a, maxrate_b;

	/* WPA/WPA2 support preferred */
	wpa_a = wpa_scan_get_vendor_ie(wa, WPA_IE_VENDOR_TYPE) != NULL ||
		wpa_scan_get_ie(wa, WLAN_EID_RSN) != NULL;
	wpa_b = wpa_scan_get_vendor_ie(wb, WPA_IE_VENDOR_TYPE) != NULL ||
		wpa_scan_get_ie(wb, WLAN_EID_RSN) != NULL;

	if (wpa_b && !wpa_a)
		return 1;
	if (!wpa_b && wpa_a)
		return -1;

	/* privacy support preferred */
	if ((wa->caps & IEEE80211_CAP_PRIVACY) == 0 &&
	    (wb->caps & IEEE80211_CAP_PRIVACY))
		return 1;
	if ((wa->caps & IEEE80211_CAP_PRIVACY) &&
	    (wb->caps & IEEE80211_CAP_PRIVACY) == 0)
		return -1;

	/* best/max rate preferred if signal level close enough XXX */
	maxrate_a = wpa_scan_get_max_rate(wa);
	maxrate_b = wpa_scan_get_max_rate(wb);
	if (maxrate_a != maxrate_b && abs(wb->level - wa->level) < 5)
		return maxrate_b - maxrate_a;

	/* use freq for channel preference */

	/* all things being equal, use signal level; if signal levels are
	 * identical, use quality values since some drivers may only report
	 * that value and leave the signal level zero */
	if (wb->level == wa->level)
		return wb->qual - wa->qual;
	return wb->level - wa->level;
}


void wpa_scan_sort_results(struct wpa_scan_results *res)
{
	qsort(res->res, res->num, sizeof(struct wpa_scan_res *),
	      wpa_scan_result_compar);
}