From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.210.198 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793027162; b=ZPQxCwFXf0VRGV5tGRctAiFvWvTXfIPnkcLpStBEeYZTdwuID0z6UexsNFghL6T8P3UC kncQrc6+L0kdTEgDeTaDZu2J5gz93sB0njIrcnuR0VxyEwX+GWtTUxGHmo5m3o50qxiab eE2D/o54q/QqgAKwJLtSWw+N8XhhyXN3Gds4fx1TjJfgH0YxNyGwz7EgoWGMv1YRe3Os5 xRNDavWaDLV3i4C+x/MK0OiFPkF95ZqDGmARw8wWtwV8uhniTGKYGOZSw0fzxLpG0EgE5 5Rh5c9UUgRuxAVlfteUs0CPHsJgU8dU4GN6LSZ0rFstOUMO9hSNlE5IS63GNwr2XETQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793027162; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Received:Date:Mime-Version: X-Mailer:Message-ID:Subject:From:To:Cc:Content-Type; bh=YAQMHYEx+VaTuqm8g03RQPwUqcCWwVMwQyZo+1H6cdk=; b=SmZESAu0KAg75ugRrf3S++tepxXTvV8nCuffKjmBBzfRRiRW5E9q/rKU30dnFo2EmfXM 0Jk1M16V2qVOj1Dp0J3xjhFXSWXAXzCzoavcgZzmf3l2ndpRz5TNggBWLy+ljofvX7Ghe beFB5bg0BHRZ1K1lhp+5zT4SHgXOi5wZCutS9v6stP9MQRPP09Fd6KCZ9zDxFM0R2CaHu WTARnt5T595ykTOGW5fBrwNp+wydqoF4v/h7+PABp3p9d7hlA15/7keF5qhuW38HMPl38 cRDyR2SWjk5OjJSJtylNxzxxiVYQGDR/Do6BnC9BItLLXvd92CUsg/A8e67jh+eGkDA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=google.com; spf=pass smtp.mailfrom=flex--starchang.bounces.google.com; dkim=pass header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20251104 header.b="c/itTipw"; arc=none smtp.remote-ip=209.85.210.198 Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 92F27606A31A for ; Mon, 26 Oct 2026 15:06:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 92F27606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--starchang.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20251104 header.b=c/itTipw Received: by mail-pf1-f198.google.com with SMTP id d2e1a72fcca58-8a06bc723b1so4336384b3a.2 for ; Mon, 26 Oct 2026 08:06:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1793027161; x=1793631961; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:mime-version:date:from :to:cc:subject:date:message-id:reply-to:content-type; bh=YAQMHYEx+VaTuqm8g03RQPwUqcCWwVMwQyZo+1H6cdk=; b=c/itTipww81RdHIsFj/YLbtrmBWdREPwQvBKHtDBxe/FvZujjDlc49ZOSpWCbuJuJg 1fe+ayqma0cf4FcVygvFvMClHx59Ibi7nvqC3YSasl712c3YmKrT+h8zQc1oMa5msN49 JlMrpX03sxldPxb90AnaX1/ol8SnmWaZxJlL8F1uAeXZADGiCNNG5sUIcgoM9td31FIF CxehzBUS3wqOFKPqHnZ09ko21aNNK3IV2rxn8YB81w8rBpojAxEohSsiuirY5yr9gVSS v6kGKOmV5vHsgQkKvNhuLDXNqDR/jbUiK8NN3kxWJwVDtMvxed4I0J7wL6nase2mcz/6 ux4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793027161; x=1793631961; h=content-type:cc:to:from:subject:message-id:mime-version:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=YAQMHYEx+VaTuqm8g03RQPwUqcCWwVMwQyZo+1H6cdk=; b=BZ/S1QatkVGERxgMb+hOcmWv0UmtBDuj+zs1YqAvj9n143PdcMAmuBvtPlGmGT1Vdl XLtWO4KF5xP7kk0xKwOh/aFjGkcHszBTGBC9BdVY7YLxqC9NdOPgN0AGvWBD/fAVzfpA jYXENdGqCCn7LTsoeWjFwly7bXRV42+mkXm6TgdshbsYY3n9erCHG7jET7ed6j3sRloP jjS3qH9clorh23MDgHEh1lAAwyRzS8uqLS2OuX0C7DZYU1OKEYjvWJ8uiBKl+8XOUgd4 JhcvoEnNmSj79mbnigo4YvLQBB2gaBgrSPbyEggmThmB34OXG8JE7fHCClEkjuErIf+U FNnA== X-Forwarded-Encrypted: i=1; AKwUvBxUhLxhy7NVR02HdQAkw/0ExZ5+dj2jkpU3bwdmsLKuRa+WRdskEgOW6Ozo2PB8QiBx30w+g/qmgMgxHOk=@vger.kernel.org X-Gm-Message-State: AFq9FYLYZODyPWP5/Rp4NgPIriqV5RY6re9bFzjRz82rHVdsyyZZsJsQ 2iNMzSic5aaIucx9HZ9XuuQCNEE7lCVn2Vzgr4csLdkN3+uMaOt7KFUPLDaUZKA4xLJzwilTpwa LON0ACNd9yqXd4RWfog== X-Received: from pfbeb15.prod.google.com ([2002:a05:6a00:4c8f:b0:8a0:3171:5410]) (user=starchang job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:896:b0:880:973d:597a with SMTP id d2e1a72fcca58-8a368a9fd92mr6124603b3a.53.1793027160600; Mon, 26 Oct 2026 08:06:00 -0700 (PDT) Date: Mon, 26 Oct 2026 15:05:39 +0000 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.257.gf7497c7d27-goog Message-ID: <20261026150539.1357037-1-starchang@google.com> Subject: [PATCH net v3] net: Fix Hole-196 vulnerability by dropping unicast ARP/IP in L2 BMC From: Star Chang To: netdev@vger.kernel.org Cc: dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net, idosch@nvidia.com, horms@kernel.org, linux-kernel@vger.kernel.org, Star Chang Content-Type: text/plain; charset="UTF-8" Wi-Fi 802.11 to 802.3 frame translation allows attackers to inject unicast L3 packets or ARP payloads inside GTK-encrypted L2 broadcast and multicast (BMC) frames (the "Hole-196" vulnerability). While the `drop_unicast_in_l2_multicast` sysctl was introduced to drop unicast IPv4/IPv6 packets received over L2 BMC, it had several gaps: 1. ARP packets were not checked in `net/ipv4/arp.c`, allowing attackers to perform ARP poisoning via L2 BMC frames (`group-arp-unicast`). 2. Enforcement lacked DHCP client (UDP port 68) exemption, which could discard legitimate DHCP server responses sent via L2 broadcast. 3. Dropped packets were silently discarded without warnings or MIB stats. The issue was identified via manual code inspection and protocol security analysis of cross-station frame injection in 802.11 shared-key (GTK) networks. In laboratory testing, crafted 802.11 broadcast frames containing unicast ARP payloads (e.g. ARPOP_REQUEST / ARPOP_REPLY with tha set to a victim's unicast MAC) bypassed the existing sysctl, poisoning the victim's ARP cache. Furthermore, per RFC 2131 inspection, unconditionally dropping L2 broadcast frames carrying unicast IP addresses discards standard DHCP server responses (DHCPOFFER/DHCPACK) destined for UDP port 68 during lease negotiation. Enhance `drop_unicast_in_l2_multicast` sysctl enforcement: - Extend sysctl checks to `net/ipv4/arp.c` (`arp_process()`) to drop unsolicited ARP Replies and ARP Requests with a non-zero unicast Target Hardware Address (tha) received over L2 BMC. - Exempt Gratuitous ARP (GARP) and RFC 5227 Address Announcements (`sip == tip`) from L2 BMC unicast drop logic so they defer to the `DROP_GRATUITOUS_ARP` sysctl, preserving VRRP/HSRP router failover. - Exempt non-fragmented DHCP client traffic (UDP dest port 68) in `net/ipv4/ip_input.c` and safely reload `ip_hdr(skb)` after `pskb_may_pull()` to prevent dangling pointer access. - Log rate-limited warnings (`pr_warn_ratelimited`) and increment MIB error counters (`IPSTATS_MIB_INHDRERRORS`) for dropped frames. Fixes: 12b74dfadb5a ("ipv4: add option to drop unicast encapsulated in L2 multicast") Fixes: abbc30436d39 ("ipv6: add option to drop unicast encapsulated in L2 multicast") Signed-off-by: Star Chang --- v2 -> v3: - Add Fixes: tags for commits 12b74dfadb5a and abbc30436d39. - Reformat lines in net/ipv4/ip_input.c to adhere strictly to the 80-column limit. - CC maintainers Ido Schimmel and Simon Horman per netdev bot check. v1 -> v2: - Clarified discovery method (manual code inspection and protocol analysis) and triggering context in commit message per netdev-bot automated feedback. net/ipv4/arp.c | 29 +++++++++++++++++++++++++++++ net/ipv4/ip_input.c | 32 ++++++++++++++++++++++++++++++-- net/ipv6/ip6_input.c | 2 ++ 3 files changed, 61 insertions(+), 2 deletions(-) diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index d409f606aec0..ad23db2e2f59 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -791,6 +791,35 @@ static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb) (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip))) goto out_free_skb; +/* + * Hole-196 defense for ARP: + * If drop_unicast_in_l2_multicast sysctl is enabled on this interface, + * drop ARP Replies in L2 BMC frames, and ARP Requests in L2 BMC frames + * that specify a non-zero unicast Target Hardware Address (tha). + * + * Legitimate Gratuitous ARP (GARP) and RFC 5227 Address Announcements + * require (sip == tip) and tha matching sha (tha == sha). Only valid + * GARP frames are exempted so they defer to DROP_GRATUITOUS_ARP below. + */ + if ((skb->pkt_type == PACKET_BROADCAST || + skb->pkt_type == PACKET_MULTICAST) && + IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST)) { + bool is_valid_garp = (sip == tip) && tha && + !memcmp(tha, sha, dev->addr_len); + + if (arp->ar_op == htons(ARPOP_REPLY) && !is_valid_garp) { + net_warn_ratelimited("Drop ARP Reply in L2 BMC on %s\n", + dev->name); + goto out_free_skb; + } + if (dev->addr_len == ETH_ALEN && tha && + is_valid_ether_addr(tha) && !is_valid_garp) { + net_warn_ratelimited("Drop unicast THA ARP Req in L2 BMC on %s\n", + dev->name); + goto out_free_skb; + } + } + /* * For some 802.11 wireless deployments (and possibly other networks), * there will be an ARP proxy and gratuitous ARP frames are attacks diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c index 9860178752b8..75a5c2059632 100644 --- a/net/ipv4/ip_input.c +++ b/net/ipv4/ip_input.c @@ -456,10 +456,38 @@ static int ip_rcv_finish_core(struct net *net, * this is 802.11 protecting against cross-station spoofing (the * so-called "hole-196" attack) so do it for both. */ + /* Hole-196 defense: + * Drop unicast IP packets received over L2 BMC frames. + * Exempt DHCP client responses (UDP port 68). + */ if (in_dev && IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST)) { - drop_reason = SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST; - goto drop; + bool is_dhcp_resp = false; + + iph = ip_hdr(skb); + if (iph->protocol == IPPROTO_UDP && + !ip_is_fragment(iph) && + pskb_may_pull(skb, iph->ihl * 4 + + sizeof(struct udphdr))) { + const struct udphdr *uh; + + iph = ip_hdr(skb); + uh = (const struct udphdr *) + (skb_network_header(skb) + + iph->ihl * 4); + if (uh->dest == htons(68)) + is_dhcp_resp = true; + } + + if (!is_dhcp_resp) { + net_warn_ratelimited("Drop unicast IP %pI4 in L2 BMC on %s +", + &iph->daddr, dev->name); + __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS); + drop_reason = + SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST; + goto drop; + } } } diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c index 8972863c93ee..caf9811f6352 100644 --- a/net/ipv6/ip6_input.c +++ b/net/ipv6/ip6_input.c @@ -278,6 +278,8 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev, (skb->pkt_type == PACKET_BROADCAST || skb->pkt_type == PACKET_MULTICAST) && READ_ONCE(idev->cnf.drop_unicast_in_l2_multicast)) { + net_warn_ratelimited("IPv6: Drop unicast IP %pI6c in L2 BMC on %s\n", + &hdr->daddr, dev->name); SKB_DR_SET(reason, UNICAST_IN_L2_MULTICAST); goto err; } -- 2.56.0.257.gf7497c7d27-goog