From nobody Sun Dec 14 11:59:54 2025 Received: from localhost.localdomain (unknown [147.136.157.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E5786215077 for ; Sun, 30 Nov 2025 03:39:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=147.136.157.3 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764473987; cv=none; b=CiwEDlOv0wbFCWNvg1UMratO5U9C3r4wPf1Xa1wkd9cuwLQiGdOGZNaLf6SkQk3BGsJEw3ZDknAmQWF5cNytmDPnjv3cA1sI7Jg/+ojZw8ir6ZKbl9u7E4+Sp6ojGHhtW04kRf9STQouxQUQeASNOQtw8nZgI1K2vIUZCwxUll0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764473987; c=relaxed/simple; bh=OiwOJbJBk6q9IvkjJfVDWx3vC+KZVz4tRUwq8fXUKO8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=B/t6d+GudcE0Oxf0ShkwzwzCApusL0986mxN+GddWL0xO5ojgN4YVbHNN8/sT/p5Wg/3b7TAuX9EPK1Rb115CS4zqy1X1JAypn9ZL39GolV3Dl+px69QirL+0qMWwKZ1U2CEg0FrTqnh3WFHVnoSDyYS9/KQdUghUYTkwBp4TUo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=none smtp.mailfrom=localhost.localdomain; arc=none smtp.client-ip=147.136.157.3 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 1007) id EA9AC8B2A36; Sun, 30 Nov 2025 11:23:15 +0800 (+08) From: Jiayuan Chen To: stable@vger.kernel.org, mptcp@lists.linux.dev, matthieu.baerts@tessares.net, sashal@kernel.org, gregkh@linuxfoundation.org Cc: Jiayuan Chen , Matthieu Baerts Subject: [PATCH 6.1.y v1 1/2] mptcp: disallow MPTCP subflows from sockmap Date: Sun, 30 Nov 2025 11:23:02 +0800 Message-ID: <20251130032303.324510-2-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251130032303.324510-1-jiayuan.chen@linux.dev> References: <20251130032303.324510-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The sockmap feature allows bpf syscall from userspace, or based on bpf sockops, replacing the sk_prot of sockets during protocol stack processing with sockmap's custom read/write interfaces. ''' tcp_rcv_state_process() subflow_syn_recv_sock() tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB) bpf_skops_established <=3D=3D sockops bpf_sock_map_update(sk) <=3D=3D call bpf helper tcp_bpf_update_proto() <=3D=3D update sk_prot ''' Consider two scenarios: 1. When the server has MPTCP enabled and the client also requests MPTCP, the sk passed to the BPF program is a subflow sk. Since subflows only handle partial data, replacing their sk_prot is meaningless and will cause traffic disruption. 2. When the server has MPTCP enabled but the client sends a TCP SYN without MPTCP, subflow_syn_recv_sock() performs a fallback on the subflow, replacing the subflow sk's sk_prot with the native sk_prot. ''' subflow_ulp_fallback() subflow_drop_ctx() mptcp_subflow_ops_undo_override() ''' Subsequently, accept::mptcp_stream_accept::mptcp_fallback_tcp_ops() converts the subflow to plain TCP. For the first case, we should prevent it from being combined with sockmap by setting sk_prot->psock_update_sk_prot to NULL, which will be blocked by sockmap's own flow. For the second case, since subflow_syn_recv_sock() has already restored sk_prot to native tcp_prot/tcpv6_prot, no further action is needed. Fixes: d2f77c53342e ("mptcp: check for plain TCP sock at accept time") Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Jiayuan Chen --- net/mptcp/subflow.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 2159b5f9988f..c922bbb12bd8 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1936,6 +1936,10 @@ void __init mptcp_subflow_init(void) =20 tcp_prot_override =3D tcp_prot; tcp_prot_override.release_cb =3D tcp_release_cb_override; +#ifdef CONFIG_BPF_SYSCALL + /* Disable sockmap processing for subflows */ + tcp_prot_override.psock_update_sk_prot =3D NULL; +#endif =20 #if IS_ENABLED(CONFIG_MPTCP_IPV6) subflow_request_sock_ipv6_ops =3D tcp_request_sock_ipv6_ops; @@ -1957,6 +1961,10 @@ void __init mptcp_subflow_init(void) =20 tcpv6_prot_override =3D tcpv6_prot; tcpv6_prot_override.release_cb =3D tcp_release_cb_override; +#ifdef CONFIG_BPF_SYSCALL + /* Disable sockmap processing for subflows */ + tcpv6_prot_override.psock_update_sk_prot =3D NULL; +#endif #endif =20 mptcp_diag_subflow_init(&subflow_ulp_ops); --=20 2.43.0