mac80211: drop data frames without key on encrypted links

commit a0761a3 upstream.

If we know that we have an encrypted link (based on having had
a key configured for TX in the past) then drop all data frames
in the key selection handler if there's no key anymore.

This fixes an issue with mac80211 internal TXQs - there we can
buffer frames for an encrypted link, but then if the key is no
longer there when they're dequeued, the frames are sent without
encryption. This happens if a station is disconnected while the
frames are still on the TXQ.

Detecting that a link should be encrypted based on a first key
having been configured for TX is fine as there are no use cases
for a connection going from with encryption to no encryption.
With extended key IDs, however, there is a case of having a key
configured for only decryption, so we can't just trigger this
behaviour on a key being configured.

Cc: [email protected]
Reported-by: Jouni Malinen <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: Luca Coelho <[email protected]>
Link: https://lore.kernel.org/r/iwlwifi.20200326150855.6865c7f28a14.I9fb1d911b064262d33e33dfba730cdeef83926ca@changeid
Signed-off-by: Johannes Berg <[email protected]>
[pali: Backported to 4.19 and older versions]
Signed-off-by: Pali Rohár <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

net/mac80211/debugfs_sta.c

@@ -80,6 +80,7 @@ static const char * const sta_flag_names[] = {
 	FLAG(MPSP_OWNER),
 	FLAG(MPSP_RECIPIENT),
 	FLAG(PS_DELIVER),
+	FLAG(USES_ENCRYPTION),
 #undef FLAG
 };
 

net/mac80211/key.c

@@ -335,6 +335,7 @@ static void ieee80211_key_replace(struct ieee80211_sub_if_data *sdata,
 	if (sta) {
 		if (pairwise) {
 			rcu_assign_pointer(sta->ptk[idx], new);
+			set_sta_flag(sta, WLAN_STA_USES_ENCRYPTION);
 			sta->ptk_idx = idx;
 			ieee80211_check_fast_xmit(sta);
 		} else {

net/mac80211/sta_info.h

@@ -101,6 +101,7 @@ enum ieee80211_sta_info_flags {
 	WLAN_STA_MPSP_OWNER,
 	WLAN_STA_MPSP_RECIPIENT,
 	WLAN_STA_PS_DELIVER,
+	WLAN_STA_USES_ENCRYPTION,
 
 	NUM_WLAN_STA_FLAGS,
 };

net/mac80211/tx.c

@@ -589,10 +589,13 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(tx->skb);
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)tx->skb->data;
 
-	if (unlikely(info->flags & IEEE80211_TX_INTFL_DONT_ENCRYPT))
+	if (unlikely(info->flags & IEEE80211_TX_INTFL_DONT_ENCRYPT)) {
 		tx->key = NULL;
-	else if (tx->sta &&
-		 (key = rcu_dereference(tx->sta->ptk[tx->sta->ptk_idx])))
+		return TX_CONTINUE;
+	}
+
+	if (tx->sta &&
+	    (key = rcu_dereference(tx->sta->ptk[tx->sta->ptk_idx])))
 		tx->key = key;
 	else if (ieee80211_is_group_privacy_action(tx->skb) &&
 		(key = rcu_dereference(tx->sdata->default_multicast_key)))
@@ -653,6 +656,9 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 		if (!skip_hw && tx->key &&
 		    tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)
 			info->control.hw_key = &tx->key->conf;
+	} else if (!ieee80211_is_mgmt(hdr->frame_control) && tx->sta &&
+		   test_sta_flag(tx->sta, WLAN_STA_USES_ENCRYPTION)) {
+		return TX_DROP;
 	}
 
 	return TX_CONTINUE;