mac80211: handle deauthentication/disassociation from TDLS peer

CVE-2019-0136

When receiving a deauthentication/disassociation frame from a TDLS
peer, a station should not disconnect the current AP, but only
disable the current TDLS link if it's enabled.

Without this change, a TDLS issue can be reproduced by following the
steps as below:

1. STA-1 and STA-2 are connected to AP, bidirection traffic is running
   between STA-1 and STA-2.
2. Set up TDLS link between STA-1 and STA-2, stay for a while, then
   teardown TDLS link.
3. Repeat step #2 and monitor the connection between STA and AP.

During the test, one STA may send a deauthentication/disassociation
frame to another, after TDLS teardown, with reason code 6/7, which
means: Class 2/3 frame received from nonassociated STA.

On receive this frame, the receiver STA will disconnect the current
AP and then reconnect. It's not a expected behavior, purpose of this
frame should be disabling the TDLS link, not the link with AP.

Cc: stable@vger.kernel.org
Signed-off-by: Yu Wang <yyuwang@codeaurora.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
(backported from commit 79c92ca4)
[ Connor Kuehl: the patch context differed slightly in the new addition
  to ieee80211_rx_mgmt_disassoc(). Mainline commit 68506e9a
  "mac80211: Print text for disassociation reason" introduces some more
  information to the call to sdata_info() but Xenial does not contain that
  commit and it is not necessary to fix this CVE. So, that hunk was placed
  manually and the call to sdata_info() remains the same as it was before. ]
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/mac80211/ieee80211_i.h

@@ -2059,6 +2059,9 @@ void ieee80211_tdls_cancel_channel_switch(struct wiphy *wiphy,
 					  const u8 *addr);
 void ieee80211_teardown_tdls_peers(struct ieee80211_sub_if_data *sdata);
 void ieee80211_tdls_chsw_work(struct work_struct *wk);
+void ieee80211_tdls_handle_disconnect(struct ieee80211_sub_if_data *sdata,
+				      const u8 *peer, u16 reason);
+const char *ieee80211_get_reason_code_string(u16 reason_code);
 
 extern const struct ethtool_ops ieee80211_ethtool_ops;
 

net/mac80211/mlme.c

@@ -2733,7 +2733,7 @@ static void ieee80211_rx_mgmt_auth(struct ieee80211_sub_if_data *sdata,
 #define case_WLAN(type) \
 	case WLAN_REASON_##type: return #type
 
-static const char *ieee80211_get_reason_code_string(u16 reason_code)
+const char *ieee80211_get_reason_code_string(u16 reason_code)
 {
 	switch (reason_code) {
 	case_WLAN(UNSPECIFIED);
@@ -2798,6 +2798,11 @@ static void ieee80211_rx_mgmt_deauth(struct ieee80211_sub_if_data *sdata,
 	if (len < 24 + 2)
 		return;
 
+	if (!ether_addr_equal(mgmt->bssid, mgmt->sa)) {
+		ieee80211_tdls_handle_disconnect(sdata, mgmt->sa, reason_code);
+		return;
+	}
+
 	if (ifmgd->associated &&
 	    ether_addr_equal(mgmt->bssid, ifmgd->associated->bssid)) {
 		const u8 *bssid = ifmgd->associated->bssid;
@@ -2847,6 +2852,11 @@ static void ieee80211_rx_mgmt_disassoc(struct ieee80211_sub_if_data *sdata,
 
 	reason_code = le16_to_cpu(mgmt->u.disassoc.reason_code);
 
+	if (!ether_addr_equal(mgmt->bssid, mgmt->sa)) {
+		ieee80211_tdls_handle_disconnect(sdata, mgmt->sa, reason_code);
+		return;
+	}
+
 	sdata_info(sdata, "disassociated from %pM (Reason: %u)\n",
 		   mgmt->sa, reason_code);
 

net/mac80211/tdls.c

@@ -1963,3 +1963,26 @@ void ieee80211_tdls_chsw_work(struct work_struct *wk)
 	}
 	rtnl_unlock();
 }
+
+void ieee80211_tdls_handle_disconnect(struct ieee80211_sub_if_data *sdata,
+				      const u8 *peer, u16 reason)
+{
+	struct ieee80211_sta *sta;
+
+	rcu_read_lock();
+	sta = ieee80211_find_sta(&sdata->vif, peer);
+	if (!sta || !sta->tdls) {
+		rcu_read_unlock();
+		return;
+	}
+	rcu_read_unlock();
+
+	tdls_dbg(sdata, "disconnected from TDLS peer %pM (Reason: %u=%s)\n",
+		 peer, reason,
+		 ieee80211_get_reason_code_string(reason));
+
+	ieee80211_tdls_oper_request(&sdata->vif, peer,
+				    NL80211_TDLS_TEARDOWN,
+				    WLAN_REASON_TDLS_TEARDOWN_UNREACHABLE,
+				    GFP_ATOMIC);
+}