From nobody Sun Dec 14 06:42:56 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E4363257435; Mon, 1 Dec 2025 11:27:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764588449; cv=none; b=TqnJwlRREAZ7IfUnB8M9544wQmaKSPPR7LgPc/f7MOD0lHZoWkZqFaP4nP6qThCu94aUzntTDW3Kwq+/rpGgu5oLUs5ybpqYDhckY0BhA6jMTUQnK/vHuoDLUC08Yx6fh4Q0zNNfyhDGudKgJoQmFahT6VYw7tgJUqMaVsV3BkY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764588449; c=relaxed/simple; bh=JQUXX5BW4qXqiuVRrha08tek9Dt+2ZQBa2czDf0X98k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=G1hxMAMCyVEzbxXGJLH6JsVbAqHSgkR5fVzqG6iF39hpeLsZS0L1BbhaTKEckK2l2VrZDisFOmN89fwYDzJdoWf6Ah6ahCSlIMcfM0M4QtIdLz9ERgOGvli77JVuI4/y80U9c6Q9zcRRVjALOar8zDOXBSxnc5OR+9VzxkSrtTU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fD1T6boH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fD1T6boH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65B9BC116D0; Mon, 1 Dec 2025 11:27:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764588448; bh=JQUXX5BW4qXqiuVRrha08tek9Dt+2ZQBa2czDf0X98k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fD1T6boHipPXaq61+x6pp8eAQoQErrmiqRKv3u94raxCLxLAFWBJ+dRj41CUi+4wr eR3Y4bmqxPo5U67AGu004/jivM83Rhn0sSv+CksTdMRkBJ0B8f1hMRpv6w6kldyyu/ s+dpWoEgOwdAFPcmk2XL8p0HrZvtAwcatSS1TdBngmfUVpgjaav32CYjR0oO3+SDe0 wgqujebpUU+v4n2RCUjDtdU+O/aqT2rY3KXqMUC1tIm3+Xpq7Wj1xK77FQSC3hhHjC mE/AKIKttGort+cL2c0XmmMAmcF6YKAXgKhfvqPqNDqMcfUs0kMTeupObtdnt+CRxZ uYLfYpmbWbZjw== From: "Matthieu Baerts (NGI0)" To: stable@vger.kernel.org, gregkh@linuxfoundation.org Cc: MPTCP Upstream , Jiayuan Chen , Martin KaFai Lau , Jakub Sitnicki , "Matthieu Baerts (NGI0)" Subject: [PATCH 5.15.y] mptcp: Fix proto fallback detection with BPF Date: Mon, 1 Dec 2025 12:27:13 +0100 Message-ID: <20251201112712.3573321-2-matttbe@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025112449-untaxed-cola-39b4@gregkh> References: <2025112449-untaxed-cola-39b4@gregkh> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3965; i=matttbe@kernel.org; h=from:subject; bh=HebLo+nplxyYDjVkJCy5huL0sbJ1daH9AyM9JTwDn9g=; b=owGbwMvMwCVWo/Th0Gd3rumMp9WSGDJ1qyeGij9qfrrqA8/1OY275BOCNjRM8piflxxRV35Ee m9s6QWnjlIWBjEuBlkxRRbptsj8mc+reEu8/Cxg5rAygQxh4OIUgIkw8DH8919t3+OxiC3q+++1 PLvUgjY8f9YcdfyS0pWGSdPYui0+7WJk+BarWK78OSU+JflPhZ76r9/XbC6/EE//FtZu7OfjMv0 4OwA= X-Developer-Key: i=matttbe@kernel.org; a=openpgp; fpr=E8CB85F76877057A6E27F77AF6B7824F4269A073 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Jiayuan Chen commit c77b3b79a92e3345aa1ee296180d1af4e7031f8f upstream. 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 <=3D=3D sockops bpf_sock_map_update(sk) <=3D=3D call bpf helper tcp_bpf_update_proto() <=3D=3D 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: result from ./scripts/decode_stacktrace.sh: Reviewed-by: Jakub Sitnicki Reviewed-by: Matthieu Baerts (NGI0) ------------[ cut here ]------------ WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \ (net/mptcp/protocol.c:4005) Modules linked in: ... PKRU: 55555554 Call Trace: do_accept (net/socket.c:1989) __sys_accept4 (net/socket.c:2028 net/socket.c:2057) __x64_sys_accept (net/socket.c:2067) x64_sys_call (arch/x86/entry/syscall_64.c:41) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:9= 4) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f87ac92b83d ---[ end trace 0000000000000000 ]--- Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Signed-off-by: Jiayuan Chen Signed-off-by: Martin KaFai Lau Reviewed-by: Jakub Sitnicki Reviewed-by: Matthieu Baerts (NGI0) Cc: Link: https://patch.msgid.link/20251111060307.194196-3-jiayuan.chen@linux.d= ev [ Conflicts in protocol.c, because commit 8e2b8a9fa512 ("mptcp: don't overwrite sock_ops in mptcp_is_tcpsk()") is not in this version. It changes the logic on how and where the sock_ops is overridden in case of passive fallback. To fix this, mptcp_is_tcpsk() is modified to use the family, but first, a check of the protocol is required to continue returning 'false' in case of MPTCP socket. ] Signed-off-by: Matthieu Baerts (NGI0) --- net/mptcp/protocol.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index f89de0f7b3e5..98fd4ffe6f11 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -77,8 +77,13 @@ static u64 mptcp_wnd_end(const struct mptcp_sock *msk) static bool mptcp_is_tcpsk(struct sock *sk) { struct socket *sock =3D sk->sk_socket; + unsigned short family; =20 - if (unlikely(sk->sk_prot =3D=3D &tcp_prot)) { + if (likely(sk->sk_protocol =3D=3D IPPROTO_MPTCP)) + return false; + + family =3D READ_ONCE(sk->sk_family); + if (unlikely(family =3D=3D AF_INET)) { /* we are being invoked after mptcp_accept() has * accepted a non-mp-capable flow: sk is a tcp_sk, * not an mptcp one. @@ -89,7 +94,7 @@ static bool mptcp_is_tcpsk(struct sock *sk) sock->ops =3D &inet_stream_ops; return true; #if IS_ENABLED(CONFIG_MPTCP_IPV6) - } else if (unlikely(sk->sk_prot =3D=3D &tcpv6_prot)) { + } else if (unlikely(family =3D=3D AF_INET6)) { sock->ops =3D &inet6_stream_ops; return true; #endif --=20 2.51.0