wifi: mac80211: restrict public action ECSA frame handling

Public action extended channel switch announcement (ECSA)
frames cannot be protected well, the spec is unclear about
what should happen in the presence of stations that can
receive protected dual and stations that cannot.

Mitigate these issues by not treating public action frames
as the absolute truth, only treat them as a hint to stop
transmitting (quiet mode), and do the remainder of the CSA
handling only when receiving the next beacon (or protected
action frame) that contains the CSA; or, if it doesn't,
simply stop being quiet and continue operating normally.

This limits the exposure to malicious ECSA public action
frames, since they cannot cause a disconnect now, only a
short interruption in traffic.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240612143037.ec7ccc45903e.Ife17d55c7ecbf98060f9c52889f3c8ba48798970@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ibss.c

@@ -785,7 +785,8 @@ ieee80211_ibss_process_chanswitch(struct ieee80211_sub_if_data *sdata,
 	err = ieee80211_parse_ch_switch_ie(sdata, elems,
 					   ifibss->chandef.chan->band,
 					   vht_cap_info, &conn,
-					   ifibss->bssid, &csa_ie);
+					   ifibss->bssid, false,
+					   &csa_ie);
 	/* can't switch to destination channel, fail */
 	if (err < 0)
 		goto disconnect;

net/mac80211/ieee80211_i.h

@@ -2218,6 +2218,8 @@ void ieee80211_process_measurement_req(struct ieee80211_sub_if_data *sdata,
  * @conn: contains information about own capabilities and restrictions
  *	to decide which channel switch announcements can be accepted
  * @bssid: the currently connected bssid (for reporting)
+ * @unprot_action: whether the frame was an unprotected frame or not,
+ *	used for reporting
  * @csa_ie: parsed 802.11 csa elements on count, mode, chandef and mesh ttl.
  *	All of them will be filled with if success only.
  * Return: 0 on success, <0 on error and >0 if there is nothing to parse.
@@ -2227,7 +2229,7 @@ int ieee80211_parse_ch_switch_ie(struct ieee80211_sub_if_data *sdata,
 				 enum nl80211_band current_band,
 				 u32 vht_cap_info,
 				 struct ieee80211_conn_settings *conn,
-				 u8 *bssid,
+				 u8 *bssid, bool unprot_action,
 				 struct ieee80211_csa_ie *csa_ie);
 
 /* Suspend/resume and hw reconfiguration */

net/mac80211/mesh.c

@@ -1312,7 +1312,7 @@ ieee80211_mesh_process_chnswitch(struct ieee80211_sub_if_data *sdata,
 	memset(&params, 0, sizeof(params));
 	err = ieee80211_parse_ch_switch_ie(sdata, elems, sband->band,
 					   vht_cap_info, &conn,
-					   sdata->vif.addr,
+					   sdata->vif.addr, false,
 					   &csa_ie);
 	if (err < 0)
 		return false;

net/mac80211/mlme.c

@@ -2352,7 +2352,8 @@ ieee80211_sta_other_link_csa_disappeared(struct ieee80211_link_data *link,
 enum ieee80211_csa_source {
 	IEEE80211_CSA_SOURCE_BEACON,
 	IEEE80211_CSA_SOURCE_OTHER_LINK,
-	IEEE80211_CSA_SOURCE_ACTION,
+	IEEE80211_CSA_SOURCE_PROT_ACTION,
+	IEEE80211_CSA_SOURCE_UNPROT_ACTION,
 };
 
 static void
@@ -2393,7 +2394,9 @@ ieee80211_sta_process_chanswitch(struct ieee80211_link_data *link,
 						   current_band,
 						   bss->vht_cap_info,
 						   &link->u.mgd.conn,
-						   link->u.mgd.bssid, &csa_ie);
+						   link->u.mgd.bssid,
+						   source == IEEE80211_CSA_SOURCE_UNPROT_ACTION,
+						   &csa_ie);
 		if (res == 0) {
 			ch_switch.block_tx = csa_ie.mode;
 			ch_switch.chandef = csa_ie.chanreq.oper;
@@ -2412,12 +2415,17 @@ ieee80211_sta_process_chanswitch(struct ieee80211_link_data *link,
 		res = 1;
 	}
 
-	if (res < 0)
+	if (res < 0) {
+		/* ignore this case, not a protected frame */
+		if (source == IEEE80211_CSA_SOURCE_UNPROT_ACTION)
+			return;
 		goto drop_connection;
+	}
 
 	if (link->conf->csa_active) {
 		switch (source) {
-		case IEEE80211_CSA_SOURCE_ACTION:
+		case IEEE80211_CSA_SOURCE_PROT_ACTION:
+		case IEEE80211_CSA_SOURCE_UNPROT_ACTION:
 			/* already processing - disregard action frames */
 			return;
 		case IEEE80211_CSA_SOURCE_BEACON:
@@ -2466,9 +2474,35 @@ ieee80211_sta_process_chanswitch(struct ieee80211_link_data *link,
 		}
 	}
 
-	/* nothing to do at all - no active CSA nor a new one */
-	if (res)
+	/* no active CSA nor a new one */
+	if (res) {
+		/*
+		 * However, we may have stopped queues when receiving a public
+		 * action frame that couldn't be protected, if it had the quiet
+		 * bit set. This is a trade-off, we want to be quiet as soon as
+		 * possible, but also don't trust the public action frame much,
+		 * as it can't be protected.
+		 */
+		if (unlikely(link->u.mgd.csa.blocked_tx)) {
+			link->u.mgd.csa.blocked_tx = false;
+			ieee80211_vif_unblock_queues_csa(sdata);
+		}
 		return;
+	}
+
+	/*
+	 * We don't really trust public action frames, but block queues (go to
+	 * quiet mode) for them anyway, we should get a beacon soon to either
+	 * know what the CSA really is, or figure out the public action frame
+	 * was actually an attack.
+	 */
+	if (source == IEEE80211_CSA_SOURCE_UNPROT_ACTION) {
+		if (csa_ie.mode) {
+			link->u.mgd.csa.blocked_tx = true;
+			ieee80211_vif_block_queues_csa(sdata);
+		}
+		return;
+	}
 
 	if (link->conf->chanreq.oper.chan->band !=
 	    csa_ie.chanreq.oper.chan->band) {
@@ -7453,12 +7487,16 @@ void ieee80211_sta_rx_queued_mgmt(struct ieee80211_sub_if_data *sdata,
 					mgmt->u.action.u.chan_switch.variable,
 					ies_len, true, NULL);
 
-			if (elems && !elems->parse_error)
+			if (elems && !elems->parse_error) {
+				enum ieee80211_csa_source src =
+					IEEE80211_CSA_SOURCE_PROT_ACTION;
+
 				ieee80211_sta_process_chanswitch(link,
 								 rx_status->mactime,
 								 rx_status->device_timestamp,
 								 elems, elems,
-								 IEEE80211_CSA_SOURCE_ACTION);
+								 src);
+			}
 			kfree(elems);
 		} else if (mgmt->u.action.category == WLAN_CATEGORY_PUBLIC) {
 			struct ieee802_11_elems *elems;
@@ -7479,6 +7517,9 @@ void ieee80211_sta_rx_queued_mgmt(struct ieee80211_sub_if_data *sdata,
 					ies_len, true, NULL);
 
 			if (elems && !elems->parse_error) {
+				enum ieee80211_csa_source src =
+					IEEE80211_CSA_SOURCE_UNPROT_ACTION;
+
 				/* for the handling code pretend it was an IE */
 				elems->ext_chansw_ie =
 					&mgmt->u.action.u.ext_chan_switch.data;
@@ -7487,7 +7528,7 @@ void ieee80211_sta_rx_queued_mgmt(struct ieee80211_sub_if_data *sdata,
 								 rx_status->mactime,
 								 rx_status->device_timestamp,
 								 elems, elems,
-								 IEEE80211_CSA_SOURCE_ACTION);
+								 src);
 			}
 
 			kfree(elems);

net/mac80211/spectmgmt.c

@@ -223,7 +223,7 @@ int ieee80211_parse_ch_switch_ie(struct ieee80211_sub_if_data *sdata,
 				 enum nl80211_band current_band,
 				 u32 vht_cap_info,
 				 struct ieee80211_conn_settings *conn,
-				 u8 *bssid,
+				 u8 *bssid, bool unprot_action,
 				 struct ieee80211_csa_ie *csa_ie)
 {
 	enum nl80211_band new_band = current_band;
@@ -258,8 +258,10 @@ int ieee80211_parse_ch_switch_ie(struct ieee80211_sub_if_data *sdata,
 
 		if (!ieee80211_operating_class_to_band(new_op_class, &new_band)) {
 			new_op_class = 0;
-			sdata_info(sdata, "cannot understand ECSA IE operating class, %d, ignoring\n",
-				   ext_chansw_elem->new_operating_class);
+			if (!unprot_action)
+				sdata_info(sdata,
+					   "cannot understand ECSA IE operating class, %d, ignoring\n",
+					   ext_chansw_elem->new_operating_class);
 		} else {
 			new_chan_no = ext_chansw_elem->new_ch_num;
 			csa_ie->count = ext_chansw_elem->count;
@@ -293,9 +295,10 @@ int ieee80211_parse_ch_switch_ie(struct ieee80211_sub_if_data *sdata,
 	new_freq = ieee80211_channel_to_frequency(new_chan_no, new_band);
 	new_chan = ieee80211_get_channel(sdata->local->hw.wiphy, new_freq);
 	if (!new_chan || new_chan->flags & IEEE80211_CHAN_DISABLED) {
-		sdata_info(sdata,
-			   "BSS %pM switches to unsupported channel (%d MHz), disconnecting\n",
-			   bssid, new_freq);
+		if (!unprot_action)
+			sdata_info(sdata,
+				   "BSS %pM switches to unsupported channel (%d MHz), disconnecting\n",
+				   bssid, new_freq);
 		return -EINVAL;
 	}