cfg80211: introduce scan IE limit attribute

This patch introduces a new attribute for a wiphy that tells
userspace how long the information elements added to a probe
request frame can be at most. It also updates the at76 to
advertise that it cannot support that, and, for now until I
can fix that, iwlwifi too.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/at76c50x-usb.c

@@ -2250,6 +2250,7 @@ static int at76_init_new_device(struct at76_priv *priv,
 
 	/* mac80211 initialisation */
 	priv->hw->wiphy->max_scan_ssids = 1;
+	priv->hw->wiphy->max_scan_ie_len = 0;
 	priv->hw->wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION);
 	priv->hw->wiphy->bands[IEEE80211_BAND_2GHZ] = &at76_supported_band;
 	priv->hw->flags = IEEE80211_HW_RX_INCLUDES_FCS |

drivers/net/wireless/iwlwifi/iwl-core.c

@@ -1306,6 +1306,7 @@ int iwl_setup_mac(struct iwl_priv *priv)
 
 	hw->wiphy->custom_regulatory = true;
 	hw->wiphy->max_scan_ssids = 1;
+	hw->wiphy->max_scan_ie_len = 0; /* XXX for now */
 
 	/* Default value; 4 EDCA QOS priorities */
 	hw->queues = 4;

include/linux/nl80211.h

@@ -390,6 +390,8 @@ enum nl80211_commands {
  *
  * @NL80211_ATTR_MAX_NUM_SCAN_SSIDS: number of SSIDs you can scan with
  *	a single scan request, a wiphy attribute.
+ * @NL80211_ATTR_MAX_SCAN_IE_LEN: maximum length of information elements
+ *	that can be added to a scan request
  *
  * @NL80211_ATTR_SCAN_FREQUENCIES: nested attribute with frequencies (in MHz)
  * @NL80211_ATTR_SCAN_SSIDS: nested attribute with SSIDs, leave out for passive
@@ -507,6 +509,8 @@ enum nl80211_attrs {
 
 	NL80211_ATTR_KEY_TYPE,
 
+	NL80211_ATTR_MAX_SCAN_IE_LEN,
+
 	/* add attributes here, update the policy in nl80211.c */
 
 	__NL80211_ATTR_AFTER_LAST,

include/net/wireless.h

@@ -222,6 +222,7 @@ struct wiphy {
 
 	int bss_priv_size;
 	u8 max_scan_ssids;
+	u16 max_scan_ie_len;
 
 	/* If multiple wiphys are registered and you're handed e.g.
 	 * a regular netdev with assigned ieee80211_ptr, you won't

net/mac80211/main.c

@@ -728,7 +728,18 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
 		return NULL;
 
 	wiphy->privid = mac80211_wiphy_privid;
+
+	if (!ops->hw_scan) {
+		/* For hw_scan, driver needs to set these up. */
 		wiphy->max_scan_ssids = 4;
+
+		/* we support a maximum of 32 rates in cfg80211 */
+		wiphy->max_scan_ie_len = IEEE80211_MAX_DATA_LEN
+					 - 2 - 32 /* SSID */
+					 - 4 - 32 /* (ext) supp rates */;
+
+	}
+
 	/* Yes, putting cfg80211_bss into ieee80211_bss is a hack */
 	wiphy->bss_priv_size = sizeof(struct ieee80211_bss) -
 			       sizeof(struct cfg80211_bss);

net/mac80211/util.c

@@ -890,6 +890,8 @@ void ieee80211_send_probe_req(struct ieee80211_sub_if_data *sdata, u8 *dst,
 		*pos = rate->bitrate / 5;
 	}
 
+	/* if adding more here, adjust max_scan_ie_len */
+
 	if (ie)
 		memcpy(skb_put(skb, ie_len), ie, ie_len);
 

net/wireless/nl80211.c

@@ -181,6 +181,8 @@ static int nl80211_send_wiphy(struct sk_buff *msg, u32 pid, u32 seq, int flags,
 	NLA_PUT_STRING(msg, NL80211_ATTR_WIPHY_NAME, wiphy_name(&dev->wiphy));
 	NLA_PUT_U8(msg, NL80211_ATTR_MAX_NUM_SCAN_SSIDS,
 		   dev->wiphy.max_scan_ssids);
+	NLA_PUT_U16(msg, NL80211_ATTR_MAX_SCAN_IE_LEN,
+		    dev->wiphy.max_scan_ie_len);
 
 	nl_modes = nla_nest_start(msg, NL80211_ATTR_SUPPORTED_IFTYPES);
 	if (!nl_modes)
@@ -2528,6 +2530,11 @@ static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
 	else
 		ie_len = 0;
 
+	if (ie_len > wiphy->max_scan_ie_len) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	request = kzalloc(sizeof(*request)
 			+ sizeof(*ssid) * n_ssids
 			+ sizeof(channel) * n_channels