From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794273863; b=fKd4jom/u/qk/ICXTdfQm3qPI16LQmhXeEjy2adCjseh770mBQOBQb36Qq5miS93Q/SD 7yLNmu0xabrb1/6MzVTcUNXksrQHbaE2yPjRGhSH31BHe0QE9QBd0XWaV9Q8opdzH5kiL v4sx/pvlxym9/oJ5cbYOsYYlXLHSXxxDq5H1nZBRBLXRFijOCVuUifja0kDLKUTOUN+js P0DTjR66osmohErAapucX3GsS/FM5N++iGCZM/k3J0fvkGAYSSy5sezOn8kAge1crBN7N capXSCUQc/KV7UGmOLCKDOstZiVjhZGhcgnPVulPeCs2kgILiddaO02JKyeF+1m7NZA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794273863; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=7cj9quH0yruZg2CGqm4Y0iwMerJuAbDx+pZro9VMP9k=; b=fe3Snz53IJhGgnSKodkW4j2HrfIox17Zior1PHTDfa3Ck8jeHMu0Vc17vJwmBv95rImW RQgcdJrlu1APGIwSLaVCRLyyuzqR+Sk2gTseY/SK2fhWFirM9e2Aey57VLz7HWq3Qv3yn R6Qf5z3NEla/QJ/1STpvN47xmW/LXwySU6+ujIZKSmwbqEhj2FG7OHsymQL8yThvQ19Sk bVZDAgAneA5hbExvJ79lmCIeKnwHRyhAJrU0QfvGq2ltgJzXfgEhRPHH1AQo36AV1DK9Y cwdD/tCnNLeZH7XHJ1PH5SpPJD4UYJ/MG2tae1PaUvVwu++/TJMOzDlQsRz0EYMeF4A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=OpPPrO0P; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52DEA60A381D for ; Tue, 10 Nov 2026 01:24:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=OpPPrO0P Received: by smtp.kernel.org (Postfix) with ESMTPSA id 773B41F0089F; Tue, 10 Nov 2026 01:24:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794273863; bh=7cj9quH0yruZg2CGqm4Y0iwMerJuAbDx+pZro9VMP9k=; h=From:To:Cc:Subject:Date; b=OpPPrO0Pgk0RjBoP3Pt/kyXcOXNe/K1obmYqEDnG+yFkA2ET9UCLS8xV9klNo2eXY gjV+fGAXticIAwG+t98/9r5nd73hTlNHgiC5ybvn3aeOes1vsaSdQH692R2Ms0F8Tz eLO0StK+gU7UiY3YNMhs9FNWCVvGyataYPhOZaw3lnF6adOKviXIbEXMzrMjBD9T1K 9OqatyBjQLhwEQSI3L26YPsXxwsEtY/SymU5+eBD9zcRG7sXRVcCqTCzC3q09e3Dl/ cwDCT/sCTFU1+hqveUXWrJBv5BIfrKtSQ1GnL0ouX5eeU75VAlh5bELXEcqN9dhau5 ZtfWj8O5zy6dw== From: Sasha Levin To: yilinzhang@moonshot.ai, bug-report@moonshot.ai, jiayuan.chen@linux.dev, pabeni@redhat.com, matttbe@kernel.org Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mptcp: do not use Fast Open on MP_JOIN subflows" failed to apply to 5.15-stable tree Date: Mon, 9 Nov 2026 20:24:21 -0500 Message-ID: <20261109202421-failed-5.15-6d2cf411aba2@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 6d2cf411aba2aa0bd641b49be5b1964ac5097a50 # git commit -s git send-email --to '' --in-reply-to '20261109202421-failed-5.15-6d2cf411aba2@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 6d2cf411aba2aa0bd641b49be5b1964ac5097a50 Mon Sep 17 00:00:00 2001 From: Yilin Zhang Date: Fri, 30 Oct 2026 23:03:51 +0100 Subject: [PATCH] mptcp: do not use Fast Open on MP_JOIN subflows tcp_fastopen_create_child() hands the SYN packet itself to subflow_syn_recv_sock(). For an MP_JOIN request this takes the fatal fallback: the cloned child is destroyed and handed back with drop_req flagged, but tcp_fastopen_create_child() does not check the flag and queues it, so accept() can expose the freed child. MP_JOIN cannot use Fast Open: data on a subflow requires the completed HMAC exchange (RFC 8684, sec. 3.2). Refuse it (only the TFO path passes a SYN skb here) and let tcp_conn_request() fall back to the regular MP_JOIN handshake; also strip the Fast Open cookie from MP_JOIN SYN/ACKs. Fixes: 90bf45134d55 ("mptcp: add new sock flag to deal with join subflows") Cc: stable@vger.kernel.org Reported-by: Kimi Security Team Suggested-by: Jiayuan Chen Suggested-by: Paolo Abeni Signed-off-by: Yilin Zhang [ Moving code to avoid clearing TS and consolidating checks. ] Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20261030-mptcp-tfo-mpj-v4-1-e6eff2027342@kernel.org Signed-off-by: Paolo Abeni --- net/mptcp/subflow.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 78e886b202585..00677fb3efcdc 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -379,6 +379,10 @@ static void subflow_prep_synack(const struct sock *sk, struct request_sock *req, struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk); struct inet_request_sock *ireq = inet_rsk(req); + /* MP_JOIN cannot use TFO, do not send a cookie in the SYN/ACK */ + if (foc && mptcp_subflow_rsk(req)->mp_join) + foc->len = -1; + /* clear tstamp_ok, as needed depending on cookie */ if (foc && foc->len > -1) ireq->tstamp_ok = 0; @@ -887,6 +891,13 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk, fallback = true; } else if (subflow_req->mp_join) { + /* a SYN skb here comes from TFO, which MP_JOIN cannot use: just + * fall back to the regular path. + */ + if ((TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_ACK)) == + TCPHDR_SYN) + return NULL; + mptcp_get_options(skb, &mp_opt); if (!(mp_opt.suboptions & OPTION_MPTCP_MPJ_ACK)) fallback = true; -- 2.53.0