mac80211: drop A-MSDUs on old ciphers

With old ciphers (WEP and TKIP) we shouldn't be using A-MSDUs
since A-MSDUs are only supported if we know that they are, and
the only practical way for that is HT support which doesn't
support old ciphers.

However, we would normally accept them anyway. Since we check
the MMIC before deaggregating A-MSDUs, and the A-MSDU bit in
the QoS header is not protected in TKIP (or WEP), this enables
attacks similar to CVE-2020-24588. To prevent that, drop A-MSDUs
completely with old ciphers.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210511200110.076543300172.I548e6e71f1ee9cad4b9a37bf212ae7db723587aa@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index f14d32a5001dd14537db37485d8c5165c99d5277..8a72d48ad6e05c3bba0e00fb0be925a5d8faa43f 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -6,7 +6,7 @@
  * Copyright 2007-2010 Johannes Berg <johannes@sipsolutions.net>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
  * Copyright(c) 2015 - 2017 Intel Deutschland GmbH
- * Copyright (C) 2018-2020 Intel Corporation
+ * Copyright (C) 2018-2021 Intel Corporation
  */
 
 #include <linux/jiffies.h>
@@ -2739,6 +2739,23 @@ ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx)
        if (is_multicast_ether_addr(hdr->addr1))
                return RX_DROP_UNUSABLE;
 
+       if (rx->key) {
+               /*
+                * We should not receive A-MSDUs on pre-HT connections,
+                * and HT connections cannot use old ciphers. Thus drop
+                * them, as in those cases we couldn't even have SPP
+                * A-MSDUs or such.
+                */
+               switch (rx->key->conf.cipher) {
+               case WLAN_CIPHER_SUITE_WEP40:
+               case WLAN_CIPHER_SUITE_WEP104:
+               case WLAN_CIPHER_SUITE_TKIP:
+                       return RX_DROP_UNUSABLE;
+               default:
+                       break;
+               }
+       }
+
        return __ieee80211_rx_h_amsdu(rx, 0);
 }