cfg80211: validate key index better

Don't accept it if a key_idx < 0 snuck through, reject WEP keys with
key index 4 and 5 (which are used for IGTKs) and don't allow IGTKs
with key indices other than 4 and 5. This makes the key data match
expectations better.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/util.c

@@ -218,7 +218,7 @@ int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
 				   struct key_params *params, int key_idx,
 				   bool pairwise, const u8 *mac_addr)
 {
-	if (key_idx > 5)
+	if (key_idx < 0 || key_idx > 5)
 		return -EINVAL;
 
 	if (!pairwise && mac_addr && !(rdev->wiphy.flags & WIPHY_FLAG_IBSS_RSN))
@@ -249,7 +249,13 @@ int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
 		/* Disallow BIP (group-only) cipher as pairwise cipher */
 		if (pairwise)
 			return -EINVAL;
+		if (key_idx < 4)
+			return -EINVAL;
 		break;
+	case WLAN_CIPHER_SUITE_WEP40:
+	case WLAN_CIPHER_SUITE_WEP104:
+		if (key_idx > 3)
+			return -EINVAL;
 	default:
 		break;
 	}