This patch is a mitigation to prevent the A-MSDU spoofing vulnerability for mesh networks. The initial update to the IEEE 802.11 standard, in response to the FragAttacks, missed this case (CVE-2025-27558). It can be considered a variant of CVE-2020-24588 but for mesh networks. This patch tries to detect if a standard MSDU was turned into an A-MSDU by an adversary. This is done by parsing a received A-MSDU as a standard MSDU, calculating the length of the Mesh Control header, and seeing if the 6 bytes after this header equal the start of an rfc1042 header. If equal, this is a strong indication of an ongoing attack attempt. This defense was tested with mac80211_hwsim against a mesh network that uses an empty Mesh Address Extension field, i.e., when four addresses are used, and when using a 12-byte Mesh Address Extension field, i.e., when six addresses are used. Functionality of normal MSDUs and A-MSDUs was also tested, and confirmed working, when using both an empty and 12-byte Mesh Address Extension field. It was also tested with mac80211_hwsim that A-MSDU attacks in non-mesh networks keep being detected and prevented. Note that the vulnerability being patched, and the defense being implemented, was also discussed in the following paper and in the following IEEE 802.11 presentation: https://papers.mathyvanhoef.com/wisec2025.pdf https://mentor.ieee.org/802.11/dcn/25/11-25-0949-00-000m-a-msdu-mesh-spoof-protection.docx Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@xxxxxxxxxxx> --- net/wireless/util.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) diff --git a/net/wireless/util.c b/net/wireless/util.c index ed868c0f7..639c75c74 100644 --- a/net/wireless/util.c +++ b/net/wireless/util.c @@ -820,6 +820,31 @@ bool ieee80211_is_valid_amsdu(struct sk_buff *skb, u8 mesh_hdr) } EXPORT_SYMBOL(ieee80211_is_valid_amsdu); +static bool +is_amsdu_aggregation_attack(struct ethhdr *eth, struct sk_buff *skb, + enum nl80211_iftype iftype) +{ + int offset; + + /* Non-mesh case can be directly compared */ + if (iftype != NL80211_IFTYPE_MESH_POINT) + return ether_addr_equal(eth->h_dest, rfc1042_header); + + offset = __ieee80211_get_mesh_hdrlen(eth->h_dest[0]); + if (offset == 6) { + /* Mesh case with empty address extension field */ + return ether_addr_equal(eth->h_source, rfc1042_header); + } else if (offset + ETH_ALEN <= skb->len) { + /* Mesh case with non-empty address extension field */ + u8 temp[ETH_ALEN]; + + skb_copy_bits(skb, offset, temp, ETH_ALEN); + return ether_addr_equal(temp, rfc1042_header); + } + + return false; +} + void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list, const u8 *addr, enum nl80211_iftype iftype, const unsigned int extra_headroom, @@ -861,8 +886,10 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list, /* the last MSDU has no padding */ if (subframe_len > remaining) goto purge; - /* mitigate A-MSDU aggregation injection attacks */ - if (ether_addr_equal(hdr.eth.h_dest, rfc1042_header)) + /* mitigate A-MSDU aggregation injection attacks, to be + * checked when processing first subframe (offset == 0). + */ + if (offset == 0 && is_amsdu_aggregation_attack(&hdr.eth, skb, iftype)) goto purge; offset += sizeof(struct ethhdr); -- 2.25.1
