From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 8517030ACE6 for ; Mon, 12 Oct 2026 13:11:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791810718; cv=none; b=akLfnehtPXXHrMWBgNpu+s6j4yqoxmUqTe22KXqH4SPXN2U8hQbWUSFZH80DpfIa7r9ziUXRAGasj5fZhNuvDeRwAbax6axtvHRyGh3aRHxEWFoFeU7p8Q3gVZAddXWnioBPJx7nHUy+Z1cE1rWq9ot+lPSGYp6hqnV/b1vMZds= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791810718; c=relaxed/simple; bh=S2H32v3aSIiNtsf3NicUhJA0asvQIyj/xJTDt+zh/3s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uJUrFxfzs2BdWf7fNpFUwwwTadCZnHeyNhHUM2sBmx8tMsEFFikcS+CsJDe76xaYvJa7X9D2OETSYUFrPbMJPd0qVmaBAKfbDbdEwQjHP51G8ojodOQxXvwzwwUHedjpNmc1BdzVfpknMTyb30LSXLCct/Ed5jyOOYzTu5jkEtY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VSfxjV6k; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VSfxjV6k" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1B6B1F0089E; Mon, 12 Oct 2026 13:11:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791810717; bh=15QsKANBqhl6XUin7qfQ07aiBggi10KGLATQp2QT0S0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VSfxjV6kxSp8OGPFe6gFU93A/xIcWowa/Ec51MZBtRYa9swBQUwy6YGFc3nt21h7C I2wpIUBqiNAZH5QIO4hNXZuJKuX9XNB/37EsjqHdjAlAhV+MdH+3zYYUuFuqYhfOY7 GBeVlA18l4CNwye4lZlTUhieQuWva+ZXzVvg94L+WOgUTzTGa/WlcGCOuEo0fNGb99 ngdmY7EzWB9g/GufHnS6WKSQ60B09VKWQje/C8CgkJn3A45ZiRLR8XrTHuyQBCXe/P kTk30bzih8OnRE8wvEApm0EiPZq476banCAWj0gZOHOo3BAvVTZ0BgAYQ9FAePzK9W eDlLMpKzyjjlQ== Message-ID: <7da818ff-d263-4138-808c-e4bd23d110d6@kernel.org> Date: Mon, 12 Oct 2026 15:11:53 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net] mptcp: reset MP_JOIN subflows on missing or invalid DSS options Content-Language: fr To: T S Rameshkumar , mptcp@lists.linux.dev Cc: T S Rameshkumar References: <20261012112625.578911-1-rameshkumar.t@phytecembedded.in> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi T S, On 12/10/2026 13:26, T S Rameshkumar wrote: > Per RFC 8684 Section 3.7, fallback to regular TCP is only permitted > on the initial subflow. Additional subflows established via MP_JOIN > MUST NOT fall back to regular TCP, and if an additional subflow > encounters missing DSS mappings, corrupted mappings, or unmapped data, > it MUST be closed with a reset. > > Currently, in subflow_check_data_avail(), when an MP_JOIN subflow > receives data without DSS mapping or with invalid mappings, it branches > to the fallback label. If fallback was already performed or allowed on > the connection, the subflow bypasses reset and incorrectly accepts > plain TCP data, synthesizing a fake fallback mapping. Do you have a reproducer for this? > Fix this by explicitly checking if the subflow is a joined subflow > (subflow->mp_join || ssk != READ_ONCE(msk->first)) under the fallback > label. If so, immediately set the appropriate reset reason > (MPTCP_RST_EMIDDLEBOX on MAPPING_NODSS, MPTCP_RST_EMPTCP otherwise), > increment MPTCP_MIB_DSSRESET, and jump to reset. > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/544 > Signed-off-by: T S Rameshkumar > --- > net/mptcp/subflow.c | 24 +++++++++++++++++++++++- > 1 file changed, 23 insertions(+), 1 deletion(-) > > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c > index 78e886b20..5faab6ffd 100644 > --- a/net/mptcp/subflow.c > +++ b/net/mptcp/subflow.c > @@ -1446,7 +1446,7 @@ static bool subflow_check_data_avail(struct sock *ssk) > return false; > > fallback: > - if (!__mptcp_check_fallback(msk)) { > + if (subflow->mp_join || ssk != READ_ONCE(msk->first)) { Here you are changing the condition "did we already fallback". Is it because a fallback already happened but yet you have a second subflow? That's not consistent, and the root cause is elsewhere. Maybe it is linked to: https://lore.kernel.org/20260814-mptcp-reset-mpj-early-v1-0-3ca3260f9474@kernel.org I didn't have time to work on a v2. Cheers, Matt -- Sponsored by the NGI0 Core fund.