diff mbox series

[04/18] cfg80211: mitigate A-MSDU aggregation attacks

Message ID 20210511200110.25d93176ddaf.I9e265b597f2cd23eb44573f35b625947b386a9de@changeid (mailing list archive)
State Accepted
Delegated to: Johannes Berg
Headers show
Series mac80211/driver security fixes | expand

Commit Message

Johannes Berg May 11, 2021, 6:02 p.m. UTC 
From: Mathy Vanhoef <Mathy.Vanhoef@kuleuven.be>

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".

Note that for kernel 4.9 and above this patch depends on "mac80211:
properly handle A-MSDUs that start with a rfc1042 header". Otherwise
this patch has no impact and attacks will remain possible.

Cc: stable@vger.kernel.org
Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@kuleuven.be>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 net/wireless/util.c | 3 +++
 1 file changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 39966a873e40..7ec021a610ae 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -771,6 +771,9 @@  void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 		remaining = skb->len - offset;
 		if (subframe_len > remaining)
 			goto purge;
+		/* mitigate A-MSDU aggregation injection attacks */
+		if (ether_addr_equal(eth.h_dest, rfc1042_header))
+			goto purge;
 
 		offset += sizeof(struct ethhdr);
 		last = remaining <= subframe_len + padding;