| Message ID | 20210513070303.20253-1-nbd@nbd.name |
|---|---|
| State | New |
| Headers | show |
| Series | [5.13] mt76: validate rx A-MSDU subframes | expand |
Felix Fietkau <nbd@nbd.name> wrote: > 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 <nbd@nbd.name> Patch applied to wireless-drivers.git, thanks. 2c2bdd2372af mt76: validate rx A-MSDU subframes -- https://patchwork.kernel.org/project/linux-wireless/patch/20210513070303.20253-1-nbd@nbd.name/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
diff --git a/drivers/net/wireless/mediatek/mt76/mac80211.c b/drivers/net/wireless/mediatek/mt76/mac80211.c index 977acab0360a..03fe62837557 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); }
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 <nbd@nbd.name> --- drivers/net/wireless/mediatek/mt76/mac80211.c | 26 +++++++++++++++++++ 1 file changed, 26 insertions(+)