2021-05-31 20:31:57

by Johannes Berg

[permalink] [raw]
Subject: [PATCH v4.9 01/10] mac80211: assure all fragments are encrypted

From: Mathy Vanhoef <[email protected]>

commit 965a7d72e798eb7af0aa67210e37cf7ecd1c9cad upstream.

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: [email protected]
Signed-off-by: Mathy Vanhoef <[email protected]>
Link: https://lore.kernel.org/r/202105[email protected]changeid
Signed-off-by: Johannes Berg <[email protected]>
---
net/mac80211/rx.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index c38d68131d02..e5760492c27d 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1942,6 +1942,16 @@ 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)
{
@@ -1987,12 +1997,7 @@ 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
@@ -2034,11 +2039,7 @@ 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--) {
--
2.31.1