From mboxrd@z Thu Jan 1 00:00:00 1970 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 3CD45231829 for ; Mon, 24 Nov 2025 17:24:28 +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=1764005069; cv=none; b=VElowrpbmucifACcgMQQD/Mv7xwWc70R2HYnYCNUbB7lV2FhYWixKcAKlmASk8a8B/TWreUEu5duzc6qGFQrxiNhN05bb1LjmxQ+2Z4/swIN0eYtfUooKkQsAq76q0z6hZ6mhDVS+tn53wtlhJfSExJTS1BS0zpLwj5yenhaaLQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764005069; c=relaxed/simple; bh=tPkTnfZS7Hac+82FJ0OmB6lJ7pbjCvYwz8Sld7pxtrU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JulK1kQzSu1Ain9uUKUX0oc1E+liCqPIzEuyAOCyyZDGVCbnMEOkTlX99/zty3divnoFOxWcAWk2aR64WgVEUPQvJHFyymRmhLjlVDdVbPu5I7RcZZI7S5X1U62VLelRB+nB07mYEDZpc1V4YaEK5BelOQDesQC+Qhj+KljssAQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=otyv2CZx; 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="otyv2CZx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DC85C4CEF1; Mon, 24 Nov 2025 17:24:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764005068; bh=tPkTnfZS7Hac+82FJ0OmB6lJ7pbjCvYwz8Sld7pxtrU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=otyv2CZxMWZnCeAWgiF1chR6EJULysOJmuSJCLrM63V7LgDXfMZxLsz9VNPC1tpzK ufhJW9GVpyertmjq6hY6R7aLK82JkM1XXS9k0GP3NzuMAfiYkyzOxnxiWS+df/YEHi LmNjM5VokIB0yLEPsG2t6Jr1RD5TnTitSk5PPy0vYr1q06P70bl+2y9pbJGxJoaFbc Hujx2rYqcBBhGI51zK9nG9HC2vbSxzVAUGBC4Jr7A/KrA3f2cfwSP/KRpIl7xTMyA8 Q7ddCnz/GX93jZiLB6FXpe4XgPlE2+o0OruofqsareVcMXrda4SnYNzWxYTckuZ85j GpvPb6YCJj7Pw== From: Sasha Levin To: stable@vger.kernel.org Cc: Jiayuan Chen , Martin KaFai Lau , Jakub Sitnicki , "Matthieu Baerts (NGI0)" , Sasha Levin Subject: [PATCH 5.15.y] mptcp: Fix proto fallback detection with BPF Date: Mon, 24 Nov 2025 12:24:26 -0500 Message-ID: <20251124172426.4160679-1-sashal@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: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jiayuan Chen [ Upstream commit c77b3b79a92e3345aa1ee296180d1af4e7031f8f ] 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: result from ./scripts/decode_stacktrace.sh: ------------[ 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:94) 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.dev [ applied fix to mptcp_is_tcpsk() instead of mptcp_fallback_tcp_ops() ] Signed-off-by: Sasha Levin --- net/mptcp/protocol.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 490fd8b188894..f758fde0565a2 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -77,8 +77,9 @@ static u64 mptcp_wnd_end(const struct mptcp_sock *msk) static bool mptcp_is_tcpsk(struct sock *sk) { struct socket *sock = sk->sk_socket; + unsigned short family = READ_ONCE(sk->sk_family); - if (unlikely(sk->sk_prot == &tcp_prot)) { + if (unlikely(family == 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 +90,7 @@ static bool mptcp_is_tcpsk(struct sock *sk) sock->ops = &inet_stream_ops; return true; #if IS_ENABLED(CONFIG_MPTCP_IPV6) - } else if (unlikely(sk->sk_prot == &tcpv6_prot)) { + } else if (unlikely(family == AF_INET6)) { sock->ops = &inet6_stream_ops; return true; #endif -- 2.51.0