mac80211: support scan features for improved scan privacy

Support the new random SN and minimal probe request contents
scan flags for the case of software scan - for hardware scan
the drivers need to opt in, but may need to do only that,
depending on their implementation.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

net/mac80211/cfg.c

@@ -3486,7 +3486,7 @@ static int ieee80211_probe_client(struct wiphy *wiphy, struct net_device *dev,
 	}
 
 	local_bh_disable();
-	ieee80211_xmit(sdata, sta, skb);
+	ieee80211_xmit(sdata, sta, skb, 0);
 	local_bh_enable();
 
 	ret = 0;

net/mac80211/ieee80211_i.h

@@ -165,6 +165,7 @@ typedef unsigned __bitwise ieee80211_tx_result;
 #define TX_DROP		((__force ieee80211_tx_result) 1u)
 #define TX_QUEUED	((__force ieee80211_tx_result) 2u)
 
+#define IEEE80211_TX_NO_SEQNO		BIT(0)
 #define IEEE80211_TX_UNICAST		BIT(1)
 #define IEEE80211_TX_PS_BUFFERED	BIT(2)
 
@@ -1880,19 +1881,20 @@ void ieee80211_regulatory_limit_wmm_params(struct ieee80211_sub_if_data *sdata,
 void ieee80211_set_wmm_default(struct ieee80211_sub_if_data *sdata,
 			       bool bss_notify, bool enable_qos);
 void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
-		    struct sta_info *sta, struct sk_buff *skb);
+		    struct sta_info *sta, struct sk_buff *skb,
+		    u32 txdata_flags);
 
 void __ieee80211_tx_skb_tid_band(struct ieee80211_sub_if_data *sdata,
 				 struct sk_buff *skb, int tid,
-				 enum nl80211_band band);
+				 enum nl80211_band band, u32 txdata_flags);
 
 static inline void
 ieee80211_tx_skb_tid_band(struct ieee80211_sub_if_data *sdata,
 			  struct sk_buff *skb, int tid,
-			  enum nl80211_band band)
+			  enum nl80211_band band, u32 txdata_flags)
 {
 	rcu_read_lock();
-	__ieee80211_tx_skb_tid_band(sdata, skb, tid, band);
+	__ieee80211_tx_skb_tid_band(sdata, skb, tid, band, txdata_flags);
 	rcu_read_unlock();
 }
 
@@ -1910,7 +1912,7 @@ static inline void ieee80211_tx_skb_tid(struct ieee80211_sub_if_data *sdata,
 	}
 
 	__ieee80211_tx_skb_tid_band(sdata, skb, tid,
-				    chanctx_conf->def.chan->band);
+				    chanctx_conf->def.chan->band, 0);
 	rcu_read_unlock();
 }
 
@@ -2034,6 +2036,8 @@ void ieee80211_send_deauth_disassoc(struct ieee80211_sub_if_data *sdata,
 
 enum {
 	IEEE80211_PROBE_FLAG_DIRECTED		= BIT(0),
+	IEEE80211_PROBE_FLAG_MIN_CONTENT	= BIT(1),
+	IEEE80211_PROBE_FLAG_RANDOM_SN		= BIT(2),
 };
 
 int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,

net/mac80211/main.c

@@ -557,10 +557,19 @@ struct ieee80211_hw *ieee80211_alloc_hw_nm(size_t priv_data_len,
 	wiphy_ext_feature_set(wiphy,
 			      NL80211_EXT_FEATURE_CONTROL_PORT_OVER_NL80211);
 
-	if (!ops->hw_scan)
+	if (!ops->hw_scan) {
 		wiphy->features |= NL80211_FEATURE_LOW_PRIORITY_SCAN |
 				   NL80211_FEATURE_AP_SCAN;
-
+		/*
+		 * if the driver behaves correctly using the probe request
+		 * (template) from mac80211, then both of these should be
+		 * supported even with hw scan - but let drivers opt in.
+		 */
+		wiphy_ext_feature_set(wiphy,
+				      NL80211_EXT_FEATURE_SCAN_RANDOM_SN);
+		wiphy_ext_feature_set(wiphy,
+				      NL80211_EXT_FEATURE_SCAN_MIN_PREQ_CONTENT);
+	}
 
 	if (!ops->set_key)
 		wiphy->flags |= WIPHY_FLAG_IBSS_RSN;

net/mac80211/offchannel.c

@@ -262,7 +262,7 @@ static void ieee80211_handle_roc_started(struct ieee80211_roc_work *roc,
 	if (roc->mgmt_tx_cookie) {
 		if (!WARN_ON(!roc->frame)) {
 			ieee80211_tx_skb_tid_band(roc->sdata, roc->frame, 7,
-						  roc->chan->band);
+						  roc->chan->band, 0);
 			roc->frame = NULL;
 		}
 	} else {

net/mac80211/rx.c

@@ -3241,7 +3241,7 @@ ieee80211_rx_h_action_return(struct ieee80211_rx_data *rx)
 		}
 
 		__ieee80211_tx_skb_tid_band(rx->sdata, nskb, 7,
-					    status->band);
+					    status->band, 0);
 	}
 	dev_kfree_skb(rx->skb);
 	return RX_QUEUED;

net/mac80211/scan.c

@@ -20,6 +20,7 @@
 #include <net/sch_generic.h>
 #include <linux/slab.h>
 #include <linux/export.h>
+#include <linux/random.h>
 #include <net/mac80211.h>
 
 #include "ieee80211_i.h"
@@ -293,6 +294,7 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
 	struct cfg80211_chan_def chandef;
 	u8 bands_used = 0;
 	int i, ielen, n_chans;
+	u32 flags = 0;
 
 	req = rcu_dereference_protected(local->scan_req,
 					lockdep_is_held(&local->mtx));
@@ -331,12 +333,16 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
 	local->hw_scan_req->req.n_channels = n_chans;
 	ieee80211_prepare_scan_chandef(&chandef, req->scan_width);
 
+	if (req->flags & NL80211_SCAN_FLAG_MIN_PREQ_CONTENT)
+		flags |= IEEE80211_PROBE_FLAG_MIN_CONTENT;
+
 	ielen = ieee80211_build_preq_ies(local,
 					 (u8 *)local->hw_scan_req->req.ie,
 					 local->hw_scan_ies_bufsize,
 					 &local->hw_scan_req->ies,
 					 req->ie, req->ie_len,
-					 bands_used, req->rates, &chandef, 0);
+					 bands_used, req->rates, &chandef,
+					 flags);
 	local->hw_scan_req->req.ie_len = ielen;
 	local->hw_scan_req->req.no_cck = req->no_cck;
 	ether_addr_copy(local->hw_scan_req->req.mac_addr, req->mac_addr);
@@ -536,13 +542,24 @@ static void ieee80211_send_scan_probe_req(struct ieee80211_sub_if_data *sdata,
 					  struct ieee80211_channel *channel)
 {
 	struct sk_buff *skb;
+	u32 txdata_flags = 0;
 
 	skb = ieee80211_build_probe_req(sdata, src, dst, ratemask, channel,
 					ssid, ssid_len,
 					ie, ie_len, flags);
+
 	if (skb) {
+		if (flags & IEEE80211_PROBE_FLAG_RANDOM_SN) {
+			struct ieee80211_hdr *hdr = (void *)skb->data;
+			u16 sn = get_random_u32();
+
+			txdata_flags |= IEEE80211_TX_NO_SEQNO;
+			hdr->seq_ctrl =
+				cpu_to_le16(IEEE80211_SN_TO_SEQ(sn));
+		}
 		IEEE80211_SKB_CB(skb)->flags |= tx_flags;
-		ieee80211_tx_skb_tid_band(sdata, skb, 7, channel->band);
+		ieee80211_tx_skb_tid_band(sdata, skb, 7, channel->band,
+					  txdata_flags);
 	}
 }
 
@@ -553,7 +570,7 @@ static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 	struct ieee80211_sub_if_data *sdata;
 	struct cfg80211_scan_request *scan_req;
 	enum nl80211_band band = local->hw.conf.chandef.chan->band;
-	u32 tx_flags;
+	u32 flags = 0, tx_flags;
 
 	scan_req = rcu_dereference_protected(local->scan_req,
 					     lockdep_is_held(&local->mtx));
@@ -561,6 +578,10 @@ static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 	tx_flags = IEEE80211_TX_INTFL_OFFCHAN_TX_OK;
 	if (scan_req->no_cck)
 		tx_flags |= IEEE80211_TX_CTL_NO_CCK_RATE;
+	if (scan_req->flags & NL80211_SCAN_FLAG_MIN_PREQ_CONTENT)
+		flags |= IEEE80211_PROBE_FLAG_MIN_CONTENT;
+	if (scan_req->flags & NL80211_SCAN_FLAG_RANDOM_SN)
+		flags |= IEEE80211_PROBE_FLAG_RANDOM_SN;
 
 	sdata = rcu_dereference_protected(local->scan_sdata,
 					  lockdep_is_held(&local->mtx));
@@ -570,7 +591,7 @@ static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 			sdata, local->scan_addr, scan_req->bssid,
 			scan_req->ssids[i].ssid, scan_req->ssids[i].ssid_len,
 			scan_req->ie, scan_req->ie_len,
-			scan_req->rates[band], 0,
+			scan_req->rates[band], flags,
 			tx_flags, local->hw.conf.chandef.chan);
 
 	/*
@@ -1159,6 +1180,7 @@ int __ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 	u32 rate_masks[NUM_NL80211_BANDS] = {};
 	u8 bands_used = 0;
 	u8 *ie;
+	u32 flags = 0;
 
 	iebufsz = local->scan_ies_len + req->ie_len;
 
@@ -1175,6 +1197,9 @@ int __ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 		}
 	}
 
+	if (req->flags & NL80211_SCAN_FLAG_MIN_PREQ_CONTENT)
+		flags |= IEEE80211_PROBE_FLAG_MIN_CONTENT;
+
 	ie = kzalloc(num_bands * iebufsz, GFP_KERNEL);
 	if (!ie) {
 		ret = -ENOMEM;
@@ -1186,7 +1211,7 @@ int __ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 	ieee80211_build_preq_ies(local, ie, num_bands * iebufsz,
 				 &sched_scan_ies, req->ie,
 				 req->ie_len, bands_used, rate_masks, &chandef,
-				 0);
+				 flags);
 
 	ret = drv_sched_scan_start(local, sdata, req, &sched_scan_ies);
 	if (ret == 0) {

net/mac80211/sta_info.c

@@ -1391,7 +1391,7 @@ static void ieee80211_send_null_response(struct sta_info *sta, int tid,
 	}
 
 	info->band = chanctx_conf->def.chan->band;
-	ieee80211_xmit(sdata, sta, skb);
+	ieee80211_xmit(sdata, sta, skb, 0);
 	rcu_read_unlock();
 }
 

net/mac80211/tx.c

@@ -825,6 +825,8 @@ ieee80211_tx_h_sequence(struct ieee80211_tx_data *tx)
 	 */
 	if (!ieee80211_is_data_qos(hdr->frame_control) ||
 	    is_multicast_ether_addr(hdr->addr1)) {
+		if (tx->flags & IEEE80211_TX_NO_SEQNO)
+			return TX_CONTINUE;
 		/* driver should assign sequence number */
 		info->flags |= IEEE80211_TX_CTL_ASSIGN_SEQ;
 		/* for pure STA mode without beacons, we can do it */
@@ -1854,7 +1856,7 @@ EXPORT_SYMBOL(ieee80211_tx_prepare_skb);
  */
 static bool ieee80211_tx(struct ieee80211_sub_if_data *sdata,
 			 struct sta_info *sta, struct sk_buff *skb,
-			 bool txpending)
+			 bool txpending, u32 txdata_flags)
 {
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_tx_data tx;
@@ -1872,6 +1874,8 @@ static bool ieee80211_tx(struct ieee80211_sub_if_data *sdata,
 	led_len = skb->len;
 	res_prepare = ieee80211_tx_prepare(sdata, &tx, sta, skb);
 
+	tx.flags |= txdata_flags;
+
 	if (unlikely(res_prepare == TX_DROP)) {
 		ieee80211_free_txskb(&local->hw, skb);
 		return true;
@@ -1933,7 +1937,8 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
 }
 
 void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
-		    struct sta_info *sta, struct sk_buff *skb)
+		    struct sta_info *sta, struct sk_buff *skb,
+		    u32 txdata_flags)
 {
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
@@ -1968,7 +1973,7 @@ void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
 	}
 
 	ieee80211_set_qos_hdr(sdata, skb);
-	ieee80211_tx(sdata, sta, skb, false);
+	ieee80211_tx(sdata, sta, skb, false, txdata_flags);
 }
 
 static bool ieee80211_parse_tx_radiotap(struct ieee80211_local *local,
@@ -2289,7 +2294,7 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 	if (!ieee80211_parse_tx_radiotap(local, skb))
 		goto fail_rcu;
 
-	ieee80211_xmit(sdata, NULL, skb);
+	ieee80211_xmit(sdata, NULL, skb, 0);
 	rcu_read_unlock();
 
 	return NETDEV_TX_OK;
@@ -3648,7 +3653,7 @@ void __ieee80211_subif_start_xmit(struct sk_buff *skb,
 
 		ieee80211_tx_stats(dev, skb->len);
 
-		ieee80211_xmit(sdata, sta, skb);
+		ieee80211_xmit(sdata, sta, skb, 0);
 	}
 	goto out;
  out_free:
@@ -3867,7 +3872,7 @@ static bool ieee80211_tx_pending_skb(struct ieee80211_local *local,
 			return true;
 		}
 		info->band = chanctx_conf->def.chan->band;
-		result = ieee80211_tx(sdata, NULL, skb, true);
+		result = ieee80211_tx(sdata, NULL, skb, true, 0);
 	} else {
 		struct sk_buff_head skbs;
 
@@ -4783,7 +4788,7 @@ EXPORT_SYMBOL(ieee80211_unreserve_tid);
 
 void __ieee80211_tx_skb_tid_band(struct ieee80211_sub_if_data *sdata,
 				 struct sk_buff *skb, int tid,
-				 enum nl80211_band band)
+				 enum nl80211_band band, u32 txdata_flags)
 {
 	int ac = ieee80211_ac_from_tid(tid);
 
@@ -4800,7 +4805,7 @@ void __ieee80211_tx_skb_tid_band(struct ieee80211_sub_if_data *sdata,
 	 */
 	local_bh_disable();
 	IEEE80211_SKB_CB(skb)->band = band;
-	ieee80211_xmit(sdata, NULL, skb);
+	ieee80211_xmit(sdata, NULL, skb, txdata_flags);
 	local_bh_enable();
 }
 

net/mac80211/util.c

@@ -1433,6 +1433,9 @@ static int ieee80211_build_preq_ies_band(struct ieee80211_local *local,
 				chandef->chan->center_freq);
 	}
 
+	if (flags & IEEE80211_PROBE_FLAG_MIN_CONTENT)
+		goto done;
+
 	/* insert custom IEs that go before HT */
 	if (ie && ie_len) {
 		static const u8 before_ht[] = {
@@ -1510,6 +1513,7 @@ static int ieee80211_build_preq_ies_band(struct ieee80211_local *local,
 	return pos - buffer;
  out_err:
 	WARN_ONCE(1, "not enough space for preq IEs\n");
+ done:
 	return pos - buffer;
 }