From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from localhost.localdomain (unknown [147.136.157.0]) (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 B7D3430F80C; Wed, 5 Nov 2025 11:38:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=147.136.157.0 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762342692; cv=none; b=EeL677g3hYDjQhXZFBhPLGEbE3kRenOFFwdHPlBJN3D/rofOE6UUJJEV5A4idRToVrUW34gJtiiqJUcFjFJkRXbdyDjK3h8w8upROlDnU1BAHtHR+vIuAGwB3JW5R6zCoQlgYNbNVGBgZKunazBaZzQRqo50/cKAT0ayyAaCcpI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762342692; c=relaxed/simple; bh=9gqY/a/t3cgf+qUGFp5v6NHGkd9JXj5rvQDmdYxUHVs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SiGTLuR93QQe4VzpicD2ZO7+1fMjShyjiMzeRpaKL4INqNookrQV80czKu4UCRISmgvmlKwVxlSCIs5kyt4aJP5PBeY2m66NretDRoQbwboRjkpvo6DPeqzxRoNofCohyMUlB4+57ZeP1PXrIe2pXF8LXq4yka5GsHnSk5eeRVg= 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=147.136.157.0 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 11B918B2A0D; Wed, 5 Nov 2025 19:38:09 +0800 (+08) From: Jiayuan Chen To: mptcp@lists.linux.dev Cc: Jiayuan Chen , stable@vger.kernel.org, Jakub Sitnicki , 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 2/3] net,mptcp: fix proto fallback detection with BPF Date: Wed, 5 Nov 2025 19:36:08 +0800 Message-ID: <20251105113625.148900-3-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, 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() syn_recv_sock()/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 ''' 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_syn_recv_sock() subflow_ulp_fallback() subflow_drop_ctx() mptcp_subflow_ops_undo_override() ''' Then, this subflow can be normally used by sockmap, which replaces the native sk_prot with sockmap's custom sk_prot. The issue occurs when the user executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops(). Here, it uses sk->sk_prot to compare with the native sk_prot, but this is incorrect when sockmap is used, as we may incorrectly set sk->sk_socket->ops. This fix uses the more generic sk_family for the comparison instead. Additionally, this also prevents a WARNING from occurring: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 388 at net/mptcp/protocol.c:68 \ mptcp_stream_accept+0x34c/0x380 Modules linked in: RIP: 0010:mptcp_stream_accept+0x34c/0x380 RSP: 0018:ffffc90000cf3cf8 EFLAGS: 00010202 PKRU: 55555554 Call Trace: do_accept+0xeb/0x190 ? __x64_sys_pselect6+0x61/0x80 ? _raw_spin_unlock+0x12/0x30 ? alloc_fd+0x11e/0x190 __sys_accept4+0x8c/0x100 __x64_sys_accept+0x1f/0x30 x64_sys_call+0x202f/0x20f0 do_syscall_64+0x72/0x9a0 ? switch_fpu_return+0x60/0xf0 ? irqentry_exit_to_user_mode+0xdb/0x1e0 ? irqentry_exit+0x3f/0x50 ? clear_bhb_loop+0x50/0xa0 ? clear_bhb_loop+0x50/0xa0 ? clear_bhb_loop+0x50/0xa0 entry_SYSCALL_64_after_hwframe+0x76/0x7e ---[ end trace 0000000000000000 ]--- result from ./scripts/decode_stacktrace.sh: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \ (net-next/net/mptcp/protocol.c:4005) Modules linked in: ... PKRU: 55555554 Call Trace: do_accept (net-next/net/socket.c:1989) __sys_accept4 (net-next/net/socket.c:2028 net-next/net/socket.c:2057) __x64_sys_accept (net-next/net/socket.c:2067) x64_sys_call (net-next/arch/x86/entry/syscall_64.c:41) do_syscall_64 (net-next/arch/x86/entry/syscall_64.c:63 \ net-next/arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (net-next/arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f87ac92b83d ---[ end trace 0000000000000000 ]--- Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Cc: Signed-off-by: Jiayuan Chen Reviewed-by: Jakub Sitnicki --- net/mptcp/protocol.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 4cd5df01446e..b5e5e130b158 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -61,11 +61,13 @@ static u64 mptcp_wnd_end(const struct mptcp_sock *msk) static const struct proto_ops *mptcp_fallback_tcp_ops(const struct sock *sk) { + unsigned short family = READ_ONCE(sk->sk_family); + #if IS_ENABLED(CONFIG_MPTCP_IPV6) - if (sk->sk_prot == &tcpv6_prot) + if (family == AF_INET6) return &inet6_stream_ops; #endif - WARN_ON_ONCE(sk->sk_prot != &tcp_prot); + WARN_ON_ONCE(family != AF_INET); return &inet_stream_ops; } -- 2.43.0