From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from localhost.localdomain (unknown [147.136.157.1]) (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 E94E326F2A1; Wed, 5 Nov 2025 11:46:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=147.136.157.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762343207; cv=none; b=IJEPPLmMpkyrr8etPPUzQq7PvrHemtP6axQr0udsyx7axpr33xWb1zCT0aNCMflwuOVgHRGYNCF8Hu7jCcRIeShH9ozBPQP6Nkc4BwlMFsddI9H+hBQopb+GUqroFIM/0SgOZJp2RJW1AohHFrmai01ACAcd/w+oo9slmIWT2gE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762343207; c=relaxed/simple; bh=hkfHasFk7m70dEz22ujbyfyr/wCs7n1zVvGYo0pWuyk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eqkFxfOvCmYe3OUNg9Qlru8WrfRro4vu4sc7Ub1+NUpbhhnH7h57xLgNmY/FFHreRVgeBVuKkvMOnwTkqd0rpV1vUpsiPOtXog63QFVb1cD055UZsWlmeFtsmTwbchNu38UmkZUT2qVVkcXKiLFc2BJwd4wFDcfz74bN1EdJ5nk= 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=147.136.157.1 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 A3AD38B2A0C; Wed, 5 Nov 2025 19:38:04 +0800 (+08) From: Jiayuan Chen To: mptcp@lists.linux.dev Cc: Jiayuan Chen , stable@vger.kernel.org, Matthieu Baerts , Mat Martineau , Geliang Tang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Florian Westphal , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net v4 1/3] mptcp: disallow MPTCP subflows from sockmap Date: Wed, 5 Nov 2025 19:36:07 +0800 Message-ID: <20251105113625.148900-2-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251105113625.148900-1-jiayuan.chen@linux.dev> References: <20251105113625.148900-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The sockmap feature allows bpf syscall from userspace using , 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 <== sockops bpf_sock_map_update(sk) <== call bpf helper tcp_bpf_update_proto() <== 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: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Cc: 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 30961b3d1702..ddd0fc6fcf45 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -2144,6 +2144,10 @@ void __init mptcp_subflow_init(void) tcp_prot_override = tcp_prot; tcp_prot_override.release_cb = tcp_release_cb_override; tcp_prot_override.diag_destroy = tcp_abort_override; +#ifdef CONFIG_BPF_SYSCALL + /* Disable sockmap processing for subflows */ + tcp_prot_override.psock_update_sk_prot = NULL; +#endif #if IS_ENABLED(CONFIG_MPTCP_IPV6) /* In struct mptcp_subflow_request_sock, we assume the TCP request sock @@ -2180,6 +2184,10 @@ void __init mptcp_subflow_init(void) tcpv6_prot_override = tcpv6_prot; tcpv6_prot_override.release_cb = tcp_release_cb_override; tcpv6_prot_override.diag_destroy = tcp_abort_override; +#ifdef CONFIG_BPF_SYSCALL + /* Disable sockmap processing for subflows */ + tcpv6_prot_override.psock_update_sk_prot = NULL; +#endif #endif mptcp_diag_subflow_init(&subflow_ulp_ops); -- 2.43.0