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 9A4FE3CAA50 for ; Tue, 26 May 2026 07:48:26 +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=1779781708; cv=none; b=jNrJyMQQZ1oD0FauJDeQNx6LGQIYaSfFrSENkH7NgP0MiCt39C2V3KTVOpnVdkFF1Co/IaF+/phDmKKb3KXHfIhnZeiJbJDbHpUXaohakfwsmm1OcdO7XmUlptTa6Wcwr/HMxTVIta7wAu5u1UApwGmnuUUyChU81It8o3RzfOg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779781708; c=relaxed/simple; bh=877DW5zm9eYrSagFXzzZ27MlckS0PAXBoyjUE25WyP4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ka6cF/LxOZNBd9PeZxR37B5BDKes9D/GygUdEvkWEn9SPHuKVBUr46R/ssrA84eTHN56rX/wXfr4VsxcFzBimRT3WJLjdrIRDWmgKBWP4PyCw4Be/7uAjn252IkLSfuCD8EoOfM8saxFoUCQDxmxnE4rViiUkz0vsZEBXYiENvs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hdxUbZE5; 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="hdxUbZE5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C75421F00A3A; Tue, 26 May 2026 07:48:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779781706; bh=kvrpAxbiMNZ3sNGwiJC92247Bo0RuF8o+I8oVPPwrCs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=hdxUbZE5PpoCxvIvIkXK7GHkF/YcyGSNw4aK1NeDK23o52vUXUTqAWO3Onc+40/i1 hA4+j/zYNEx/WgOaN+C3kt+J5fBow7GtfmK0WfxxGwf0axwhDyxROygOETveZAF6Lu EGufVbyvT0AOXoRkB3i2zKMTxeb7Je5TH3nRupeHiyNIQ0VhC/BfkYXtRSTIdLUp0A hA9BynapZsqd0GEn7lY1FPVnwupjXW0PYvcKWwEy79RGg62EySyu08Lt+F8//0yAtJ LQE3uxvVr+Xqlon1JF+Iw1jBzX6soFLxQYfnbFW0Gcc02SGqMQtoH8cyXTNVO2KgFJ A7pBRhGd7B2oA== Message-ID: Date: Tue, 26 May 2026 17:48:22 +1000 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 v8 mptcp-next 4/9] mptcp: allow subflow rcv wnd to shrink Content-Language: fr To: Paolo Abeni , mptcp@lists.linux.dev Cc: Geliang Tang , gang.yan@linux.dev References: <661603fa10737a624bba854fb2515c7abb129a80.1779485511.git.pabeni@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 23/05/2026 07:43, Paolo Abeni wrote: > In MPTCP connection, the `window` field in the TCP header refers to the > MPTCP-level rcv_nxt and it's right edge should not move backward. Such > constraint is enforced at DSS option generation time. > > At the same time, the TCP stack ensures independently that the TCP-level > rcv wnd right's edge does not move backward. That in turn causes artificial > inflating of the MPTCP rcv window when the incoming data is acked at the > TCP level and is OoO in the MPTCP sequence space (or lands in the backlog). > > As a consequence, the incoming traffic can exceed the receiver rcvbuf size > even when the sender is not misbehaving. > > Prevent such scenario forcibly allowing the TCP subflow to shrink the > TCP-level rcv wnd regardless of the current netns setting. > > Fixes: f3589be0c420 ("mptcp: never shrink offered window") > Signed-off-by: Paolo Abeni > --- > net/mptcp/options.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/net/mptcp/options.c b/net/mptcp/options.c > index 4d72f286a485..97ea4aa37b33 100644 > --- a/net/mptcp/options.c > +++ b/net/mptcp/options.c > @@ -566,6 +566,7 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, > { > struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk); > struct mptcp_sock *msk = mptcp_sk(subflow->conn); > + struct tcp_sock *tp = tcp_sk(sk); > unsigned int dss_size = 0; > struct mptcp_ext *mpext; > unsigned int ack_size; > @@ -614,6 +615,12 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, > if (dss_size == 0) > ack_size += TCPOLEN_MPTCP_DSS_BASE; > > + /* The caller is __tcp_transmit_skb(), and will compute the new rcv > + * wnd soon: ensure that the window can shrink. > + */ > + if (skb) > + tp->rcv_wnd = tp->rcv_nxt - tp->rcv_wup; Do you need to call tcp_update_max_rcv_wnd_seq() after having updated rcv_wnd? See 0e24d17bd966 ("tcp: implement RFC 7323 window retraction receiver requirements") for more details about it. If we do that, I guess we can declare "struct tcp_sock *tp" here in the if-statement. I can also update the patch when applying it. Apart from that: Reviewed-by: Matthieu Baerts (NGI0) Cheers, Matt -- Sponsored by the NGI0 Core fund.