mac80211: assure all fragments are encrypted

Do not mix plaintext and encrypted fragments in protected Wi-Fi
networks. This fixes CVE-2020-26147.

Previously, an attacker was able to first forward a legitimate encrypted
fragment towards a victim, followed by a plaintext fragment. The
encrypted and plaintext fragment would then be reassembled. For further
details see Section 6.3 and Appendix D in the paper "Fragment and Forge:
Breaking Wi-Fi Through Frame Aggregation and Fragmentation".

Because of this change there are now two equivalent conditions in the
code to determine if a received fragment requires sequential PNs, so we
also move this test to a separate function to make the code easier to
maintain.

Cc: stable@vger.kernel.org
Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@kuleuven.be>
Link: https://lore.kernel.org/r/20210511200110.30c4394bb835.I5acfdb552cc1d20c339c262315950b3eac491397@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 62047e93e217be086cada92237b978f614eaa29e..65fc674e27cc0340750565e53745f2303a66178b 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2194,6 +2194,16 @@ ieee80211_reassemble_find(struct ieee80211_sub_if_data *sdata,
        return NULL;
 }
 
+static bool requires_sequential_pn(struct ieee80211_rx_data *rx, __le16 fc)
+{
+       return rx->key &&
+               (rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP ||
+                rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP_256 ||
+                rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP ||
+                rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP_256) &&
+               ieee80211_has_protected(fc);
+}
+
 static ieee80211_rx_result debug_noinline
 ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 {
@@ -2238,12 +2248,7 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
                /* This is the first fragment of a new frame. */
                entry = ieee80211_reassemble_add(rx->sdata, frag, seq,
                                                 rx->seqno_idx, &(rx->skb));
-               if (rx->key &&
-                   (rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP ||
-                    rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP_256 ||
-                    rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP ||
-                    rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP_256) &&
-                   ieee80211_has_protected(fc)) {
+               if (requires_sequential_pn(rx, fc)) {
                        int queue = rx->security_idx;
 
                        /* Store CCMP/GCMP PN so that we can verify that the
@@ -2285,11 +2290,7 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
                u8 pn[IEEE80211_CCMP_PN_LEN], *rpn;
                int queue;
 
-               if (!rx->key ||
-                   (rx->key->conf.cipher != WLAN_CIPHER_SUITE_CCMP &&
-                    rx->key->conf.cipher != WLAN_CIPHER_SUITE_CCMP_256 &&
-                    rx->key->conf.cipher != WLAN_CIPHER_SUITE_GCMP &&
-                    rx->key->conf.cipher != WLAN_CIPHER_SUITE_GCMP_256))
+               if (!requires_sequential_pn(rx, fc))
                        return RX_DROP_UNUSABLE;
                memcpy(pn, entry->last_pn, IEEE80211_CCMP_PN_LEN);
                for (i = IEEE80211_CCMP_PN_LEN - 1; i >= 0; i--) {