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>
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index fbcbed6..ee58a78 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -728,7 +728,18 @@
 		return NULL;
 
 	wiphy->privid = mac80211_wiphy_privid;
-	wiphy->max_scan_ssids = 4;
+
+	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);
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index fdf432f..05caf34 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -890,6 +890,8 @@
 		*pos = rate->bitrate / 5;
 	}
 
+	/* if adding more here, adjust max_scan_ie_len */
+
 	if (ie)
 		memcpy(skb_put(skb, ie_len), ie, ie_len);
 
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 1394115..447fa17 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -181,6 +181,8 @@
 	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 @@
 	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