wpa_supplicant: Check rate sets before joining BSS

IEEE Std 802.11-2007 7.3.2.2 demands that in order to join a BSS all
required basic rates have to be supported by the hardware.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>

diff --git a/wpa_supplicant/events.c b/wpa_supplicant/events.c
index 3d88027..5831fbf 100644 (file)
--- a/wpa_supplicant/events.c
+++ b/wpa_supplicant/events.c
@@ -478,6 +478,112 @@ static int freq_allowed(int *freqs, int freq)
 }
 
 
+static int ht_supported(const struct hostapd_hw_modes *mode)
+{
+       if (!(mode->flags & HOSTAPD_MODE_FLAG_HT_INFO_KNOWN)) {
+               /*
+                * The driver did not indicate whether it supports HT. Assume
+                * it does to avoid connection issues.
+                */
+               return 1;
+       }
+
+       /*
+        * IEEE Std 802.11n-2009 20.1.1:
+        * An HT non-AP STA shall support all EQM rates for one spatial stream.
+        */
+       return mode->mcs_set[0] == 0xff;
+}
+
+
+static int rate_match(struct wpa_supplicant *wpa_s, struct wpa_scan_res *bss)
+{
+       const struct hostapd_hw_modes *mode = NULL, *modes;
+       const u8 scan_ie[2] = { WLAN_EID_SUPP_RATES, WLAN_EID_EXT_SUPP_RATES };
+       const u8 *rate_ie;
+       int i, j, k;
+
+       modes = wpa_s->hw.modes;
+       if (modes == NULL) {
+               /*
+                * The driver does not provide any additional information
+                * about the utilized hardware, so allow the connection attempt
+                * to continue.
+                */
+               return 1;
+       }
+
+       for (i = 0; i < wpa_s->hw.num_modes; i++) {
+               for (j = 0; j < modes[i].num_channels; j++) {
+                       int freq = modes[i].channels[j].freq;
+                       if (freq == bss->freq) {
+                               if (mode &&
+                                   mode->mode == HOSTAPD_MODE_IEEE80211G)
+                                       break; /* do not allow 802.11b replace
+                                               * 802.11g */
+                               mode = &modes[i];
+                               break;
+                       }
+               }
+       }
+
+       if (mode == NULL)
+               return 0;
+
+       for (i = 0; i < (int) sizeof(scan_ie); i++) {
+               rate_ie = wpa_scan_get_ie(bss, scan_ie[i]);
+               if (rate_ie == NULL)
+                       continue;
+
+               for (j = 2; j < rate_ie[1] + 2; j++) {
+                       int flagged = !!(rate_ie[j] & 0x80);
+                       int r = (rate_ie[j] & 0x7f) * 5;
+
+                       /*
+                        * IEEE Std 802.11n-2009 7.3.2.2:
+                        * The new BSS Membership selector value is encoded
+                        * like a legacy basic rate, but it is not a rate and
+                        * only indicates if the BSS members are required to
+                        * support the mandatory features of Clause 20 [HT PHY]
+                        * in order to join the BSS.
+                        */
+                       if (flagged && ((rate_ie[j] & 0x7f) ==
+                                       BSS_MEMBERSHIP_SELECTOR_HT_PHY)) {
+                               if (!ht_supported(mode)) {
+                                       wpa_dbg(wpa_s, MSG_DEBUG,
+                                               "   hardware does not support "
+                                               "HT PHY");
+                                       return 0;
+                               }
+                               continue;
+                       }
+
+                       if (!flagged)
+                               continue;
+
+                       /* check for legacy basic rates */
+                       for (k = 0; k < mode->num_rates; k++) {
+                               if (mode->rates[k] == r)
+                                       break;
+                       }
+                       if (k == mode->num_rates) {
+                               /*
+                                * IEEE Std 802.11-2007 7.3.2.2 demands that in
+                                * order to join a BSS all required rates
+                                * have to be supported by the hardware.
+                                */
+                               wpa_dbg(wpa_s, MSG_DEBUG, "   hardware does "
+                                       "not support required rate %d.%d Mbps",
+                                       r / 10, r % 10);
+                               return 0;
+                       }
+               }
+       }
+
+       return 1;
+}
+
+
 static struct wpa_ssid * wpa_scan_res_match(struct wpa_supplicant *wpa_s,
                                            int i, struct wpa_scan_res *bss,
                                            struct wpa_ssid *group)
@@ -610,6 +716,12 @@ static struct wpa_ssid * wpa_scan_res_match(struct wpa_supplicant *wpa_s,
                        continue;
                }
 
+               if (!rate_match(wpa_s, bss)) {
+                       wpa_dbg(wpa_s, MSG_DEBUG, "   skip - rate sets do "
+                               "not match");
+                       continue;
+               }
+
 #ifdef CONFIG_P2P
                /*
                 * TODO: skip the AP if its P2P IE has Group Formation