From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lj1-f176.google.com (mail-lj1-f176.google.com [209.85.208.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2B4D733DEF2 for ; Mon, 4 May 2026 22:53:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777935211; cv=none; b=oCTOogZn31sAKxbzxRWnUNJU9YCh1IeJ+4e+8dAdhj3AY2aa6gEvvjE40kO7HTZYptbAkVJQzJUQvrTuDVfRLX2u7iYgVMlpov6TKyursE/NYPjmvJlNm/Q5sEVtS6t7VjWpSbsDyrS4oQs7CPCxy4vVqGnQ6YmHKv9vhKrHLIk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777935211; c=relaxed/simple; bh=kl+VKiVcXFJLGz+zh1YjrPpBSIjFpq/0QZXFRB4vlQY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lcygyQxTpLIF0vT2Pb2VLBf9nylIHg5fdx5xPc9X6HksB8viPYOquwF2WQ+KLmfj+Jm6HFohWonMQ68PBwXetxJ0axDh2SnOVrtjPESCRjJglDY68Uc+i8GmuCifygNYc7q1+33S3WieP+cOB0G3/yyWrGghTW78SkJNVHAm1ok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=jbR+Aan6; arc=none smtp.client-ip=209.85.208.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jbR+Aan6" Received: by mail-lj1-f176.google.com with SMTP id 38308e7fff4ca-393925cb1baso22601601fa.0 for ; Mon, 04 May 2026 15:53:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1777935208; x=1778540008; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=po4u7/Rujwbm7uihMqIsA/eo7S1xmgz8pQV0r2hhPeo=; b=jbR+Aan6NTM1C9bwGODvJC8obmEzJ3T2agwcKRY4Yu+jfsw6TGxwHJwz88l00iwB8r /Gq765gHp6mVwO04u9LDvU/IOPh2pFWnXY4xjXapPRKgxAmLkZvMha7JClIkXETsr2Rf n+2gNrIiMxyGFB3RX8hi02ct2IFKj0NhuSnVtGoFDuZhypdOY9QoUZ/+FIrMQPsEby4F +LbHpvRrhYA6kOYAM2qccs7KZ+G0Bo1d6dU87D+eh2l7HD3PrjIxaq88bHNOX5RukbVC MWSIxaWa2H8i/NAub38P9zgAphw3FaavAF1X4wUrFP/897kbxkmTqDECF5ii0gVTp0xC eY5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777935208; x=1778540008; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=po4u7/Rujwbm7uihMqIsA/eo7S1xmgz8pQV0r2hhPeo=; b=RBhQk8NwAo4ld7vmadhr0EVoMbvFZzcuQZ0mcaBUaVOmzd0u3CZoMFF5yFnubX7wuT yXZQI+jOlNoWtne/mzEbuKXtToBpjtj1HKKB1RJi+ZlaQPNeVgXAjwUjCIG55U/sVaYa 0rPc6KyOq711JFwDWKoZHB+PwIpMLFPJsk70LoOZ5vQ8bbboNQ6za5ndFhwPcGlI2x5w dt3qx9Vc0uc1HttzLcNwJvBGxTHzE079OUXThydiF1H0fWuvUl5P2+G8ZYMKnLdSK+3u GY+V0Ks94q89k0RqlZ01YkgigZtV8VuTfQwzx6oeHcRWajWORiKmrEJSpgfBdy/x5NjF Bdng== X-Gm-Message-State: AOJu0Yxlla3p6Jp/0uLVPEF1PACZukdpxphXUUD8Lqrxc1gGaOkOSE7/ TG9gSYIQGRhRVPCzg1MWwec7EJD4bpeCJsLr8jLnYUydu6gt/d0yUEQe73HLCp6koZw= X-Gm-Gg: AeBDiets299jivA3Fwu578HIoZxS+yFz0rMd3PkbiAVuPVxnJRDit4XBQ2w/o4AiuaF xotSHl0p7ySKl9rmVMNrevjmIr24wLvGNPaKC/a5PxEoYjdl/Q5UBnu4hA5WJBQ8Wmrn72/DhMJ PUeiR4RT8AAafhEbJM0IcfVnfTUoI9z5gfgapHxF7KGBAJp0FmZu/7WEbCpi1nlu5NbmbQMCmeN ZN598bkEHIKBVbmMB+VNxdkJM4yPGwRbao+tuFlTWoaOTu4gBbgjG2qDodneGvkOLfD7vlOajmS Iyu/1lpB8YTpuHu3wsKNyFHqYV2yq4z9Qc5I1X2zrrgPpwUYFfRGsV1N8e5R0IQww+NTXFuBF+P RM1Duc9Tr7sisjq35KPst//vWZL0ti2zULa3QEcn8lIukbrPJskDSe2buTtOVxP1w17ZWPmRf6c vjar81jorwUhzwawyThAY2GgOBFRcNxIIh4qyCb/6AaScLfoLtgefkL0HnOmemwPFJB1i5nb2Fz qRBIwH39qRlvn3STF0xPOYJ X-Received: by 2002:a05:651c:2116:b0:38a:45d6:c246 with SMTP id 38308e7fff4ca-393783ef512mr45088291fa.8.1777935207897; Mon, 04 May 2026 15:53:27 -0700 (PDT) Received: from dau-home-pc.megasoftware.org ([46.246.34.10]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3939b43a795sm15774901fa.35.2026.05.04.15.53.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 15:53:26 -0700 (PDT) From: Anton Danilov To: netdev@vger.kernel.org Cc: Willem de Bruijn , davem@davemloft.net, David Ahern , Eric Dumazet , Kuniyuki Iwashima , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , linux-kselftest@vger.kernel.org Subject: [RFC PATCH net-next v3 0/2] udp: fix FOU/GUE over multicast Date: Tue, 5 May 2026 01:53:08 +0300 Message-ID: X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit UDP encapsulation (FOU, GUE) has never worked correctly with multicast destination addresses. When a FOU-encapsulated packet arrives at a multicast address, it enters __udp4_lib_mcast_deliver() which calls consume_skb() on packets that need resubmission to the inner protocol handler, silently dropping them instead. The unicast delivery path handles this correctly by returning -ret, but the multicast path was never updated to support UDP encapsulation resubmit. This causes silent packet loss for FOU/GRETAP tunnels configured with multicast remote addresses. The loss ratio depends on the early demux cache hit rate - packets that hit early demux bypass the multicast path and work correctly, masking the issue. Reproducing the issue: ip netns add ns_a && ip netns add ns_b ip link add veth0 type veth peer name veth1 ip link set veth0 netns ns_a && ip link set veth1 netns ns_b ip -n ns_a addr add 10.0.0.1/24 dev veth0 && ip -n ns_a link set veth0 up ip -n ns_b addr add 10.0.0.2/24 dev veth1 && ip -n ns_b link set veth1 up # Multicast routes ip -n ns_a route add 239.0.0.0/8 dev veth0 ip -n ns_b route add 239.0.0.0/8 dev veth1 # Disable early demux to expose the issue (otherwise it's partially masked) ip netns exec ns_b sysctl -w net.ipv4.ip_early_demux=0 # Join multicast group on receiver ip -n ns_b addr add 239.0.0.1/32 dev veth1 autojoin # Sender: GRETAP with FOU encap ip -n ns_a link add eoudp0 type gretap \ remote 239.0.0.1 local 10.0.0.1 \ encap fou encap-sport 4797 encap-dport 4797 key 239.0.0.1 ip -n ns_a link set eoudp0 up ip -n ns_a addr add 192.168.99.1/24 dev eoudp0 # Receiver: FOU listener + GRETAP ip netns exec ns_b ip fou add port 4797 ipproto 47 ip -n ns_b link add eoudp0 type gretap \ remote 239.0.0.1 local 10.0.0.2 \ encap fou encap-sport 4797 encap-dport 4797 key 239.0.0.1 ip -n ns_b link set eoudp0 up ip -n ns_b addr add 192.168.99.2/24 dev eoudp0 # Static neigh: ARP replies can't traverse unidirectional mcast tunnel recv_mac=$(ip -n ns_b link show eoudp0 | awk '/ether/{print $2}') ip -n ns_a neigh add 192.168.99.2 lladdr $recv_mac dev eoudp0 # Test: ping through the FOU/GRETAP tunnel ip netns exec ns_a ping -c 100 192.168.99.2 # -> without this patch: 0 packets received on eoudp0 # -> with this patch: all packets received on eoudp0 AI assistance (Claude, claude-opus-4-6) was used during root cause analysis of the kernel source code (tracing the call chain from udp_queue_rcv_skb through encap_rcv to ip_protocol_deliver_rcu, comparing unicast/GSO/multicast paths) and during patch and selftest authoring. The fix approach was identified by observing that the unicast path (udp_unicast_rcv_skb) already handles encap resubmit correctly via return -ret, while the multicast path did not. Changes since v2: - Use return -ret instead of calling ip_protocol_deliver_rcu() directly, matching the unicast path and avoiding call stack growth with nested encapsulations (Eric Dumazet) - Only change the first-socket path; the clone loop is not reachable for tunnel sockets (no SO_REUSEADDR/SO_REUSEPORT) - Replace Python packet generator with ping through a properly configured FOU/GRETAP tunnel in the selftest - Add static neighbor entry in the test (ARP replies cannot traverse the unidirectional multicast tunnel) Changes since v1 (RFC): - Moved inline Python packet generator into a separate helper - Fixed author email typo in Signed-off-by Anton Danilov (2): udp: fix encapsulation packet resubmit in multicast deliver selftests: net: add FOU multicast encapsulation resubmit test net/ipv4/udp.c | 6 +- net/ipv6/udp.c | 6 +- tools/testing/selftests/net/Makefile | 1 + .../testing/selftests/net/fou_mcast_encap.sh | 112 ++++++++++++++++++ 4 files changed, 121 insertions(+), 4 deletions(-) create mode 100755 tools/testing/selftests/net/fou_mcast_encap.sh -- 2.47.3