From 2c2bdd2372afcfcf24fe11c65ebe3361b7e1cd9f Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Thu, 13 May 2021 09:03:03 +0200 Subject: [PATCH] mt76: validate rx A-MSDU subframes Mitigate A-MSDU injection attacks (CVE-2020-24588) by detecting if the destination address of a subframe equals an RFC1042 (i.e., LLC/SNAP) header, and if so dropping the complete A-MSDU frame. This mitigates known attacks, although new (unknown) aggregation-based attacks may remain possible. This defense works because in A-MSDU aggregation injection attacks, a normal encrypted Wi-Fi frame is turned into an A-MSDU frame. This means the first 6 bytes of the first A-MSDU subframe correspond to an RFC1042 header. In other words, the destination MAC address of the first A-MSDU subframe contains the start of an RFC1042 header during an aggregation attack. We can detect this and thereby prevent this specific attack. For details, see Section 7.2 of "Fragment and Forge: Breaking Wi-Fi Through Frame Aggregation and Fragmentation". Signed-off-by: Felix Fietkau Signed-off-by: Kalle Valo Link: https://lore.kernel.org/r/20210513070303.20253-1-nbd@nbd.name --- drivers/net/wireless/mediatek/mt76/mac80211.c | 26 +++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/drivers/net/wireless/mediatek/mt76/mac80211.c b/drivers/net/wireless/mediatek/mt76/mac80211.c index 977acab0360a3..03fe628375576 100644 --- a/drivers/net/wireless/mediatek/mt76/mac80211.c +++ b/drivers/net/wireless/mediatek/mt76/mac80211.c @@ -514,10 +514,36 @@ EXPORT_SYMBOL_GPL(mt76_free_device); static void mt76_rx_release_amsdu(struct mt76_phy *phy, enum mt76_rxq_id q) { struct sk_buff *skb = phy->rx_amsdu[q].head; + struct mt76_rx_status *status = (struct mt76_rx_status *)skb->cb; struct mt76_dev *dev = phy->dev; phy->rx_amsdu[q].head = NULL; phy->rx_amsdu[q].tail = NULL; + + /* + * Validate if the amsdu has a proper first subframe. + * A single MSDU can be parsed as A-MSDU when the unauthenticated A-MSDU + * flag of the QoS header gets flipped. In such cases, the first + * subframe has a LLC/SNAP header in the location of the destination + * address. + */ + if (skb_shinfo(skb)->frag_list) { + int offset = 0; + + if (!(status->flag & RX_FLAG_8023)) { + offset = ieee80211_get_hdrlen_from_skb(skb); + + if ((status->flag & + (RX_FLAG_DECRYPTED | RX_FLAG_IV_STRIPPED)) == + RX_FLAG_DECRYPTED) + offset += 8; + } + + if (ether_addr_equal(skb->data + offset, rfc1042_header)) { + dev_kfree_skb(skb); + return; + } + } __skb_queue_tail(&dev->rx_skb[q], skb); } -- 2.39.5