mac80211: use min rate as basic rate for buggy APs

Some buggy APs (and even P2P_GO) don't advertise their
basic rates in the association response.

In such case, use the min supported rate as the
basic rate.
Reported-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -1485,6 +1485,7 @@ static bool ieee80211_assoc_success(struct ieee80211_work *wk,
 	int i, j, err;
 	bool have_higher_than_11mbit = false;
 	u16 ap_ht_cap_flags;
+	int min_rate = INT_MAX, min_rate_index = -1;
 
 	/* AssocResp and ReassocResp have identical structure */
 
@@ -1551,6 +1552,10 @@ static bool ieee80211_assoc_success(struct ieee80211_work *wk,
 				rates |= BIT(j);
 				if (is_basic)
 					basic_rates |= BIT(j);
+				if (rate < min_rate) {
+					min_rate = rate;
+					min_rate_index = j;
+				}
 				break;
 			}
 		}
@@ -1568,11 +1573,25 @@ static bool ieee80211_assoc_success(struct ieee80211_work *wk,
 				rates |= BIT(j);
 				if (is_basic)
 					basic_rates |= BIT(j);
+				if (rate < min_rate) {
+					min_rate = rate;
+					min_rate_index = j;
+				}
 				break;
 			}
 		}
 	}
 
+	/*
+	 * some buggy APs don't advertise basic_rates. use the lowest
+	 * supported rate instead.
+	 */
+	if (unlikely(!basic_rates) && min_rate_index >= 0) {
+		printk(KERN_DEBUG "%s: No basic rates in AssocResp. "
+		       "Using min supported rate instead.\n", sdata->name);
+		basic_rates = BIT(min_rate_index);
+	}
+
 	sta->sta.supp_rates[wk->chan->band] = rates;
 	sdata->vif.bss_conf.basic_rates = basic_rates;