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 E1CF71EB4A; Mon, 18 Mar 2024 20:16:13 +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=1710792974; cv=none; b=J/tk47B3cuW0NaAaGPnGzzXP8Ohm07xPdp2i2nav0ywnzT9uQJVbCr95kGc1n7neMXvdhogcUY4nJxiQhs/TYfe6KH3SenKfL9cdTYpvXBcLj8IhLv3+rujsjN0beoz9oLIubTQj/kf7WXtt+4Rp5suZ0/spnspcAb75e+/tQ1E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710792974; c=relaxed/simple; bh=gg9yhJE2tKWPbbcf6g5GK2oT2v1wCetzwojpd2WVCkY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mZ85vI4LeMdKV8aNdoqqcsK4ffAoSJdeCZNNPPy6tyc1RRM/IiWAS00jO4nJTGURd3n4ebTnMyqpvWaKEspvpDmi09rJ1fekhh3zBisQIw2lFLk4kgfD0ZUAhaMS3VIE8sfD3KXLueUcdytBwpjREQ9N9luljjw7aN8IlzQ++DI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fmxU1QKr; 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="fmxU1QKr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8118C433F1; Mon, 18 Mar 2024 20:16:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710792973; bh=gg9yhJE2tKWPbbcf6g5GK2oT2v1wCetzwojpd2WVCkY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fmxU1QKrhCBFklyRsBhey4NREh5F75+rKNal5351ToUkUx+qkjqH8ZD1oCEbVA5hE MWUnZ3DadB1/5gwTYj/+BouD0ADixy0wikoxpcDS7k+7rIAGm2Z4hNU61GpMwbptaa 6UnXEyfPPvCrB1NOQiI2z44WN1YIUj1mvesJBaMMwCSfme2i9fHm+tgCpEabITSdZf iLI83IktSzZrorvnrmdOGY2qY7z2ABFq3LKtZnriLKp+0utUvkbX2oZ4E6NMpy2sye xj63iKbCywpGgNmiJZa50Ne4c4UQl1QrcQwoguoeN6zVaclpX1kAVKzccMJGu7b32r g0ECxwgugO8Gw== Date: Mon, 18 Mar 2024 20:16:08 +0000 From: Simon Horman To: Jason Xing Cc: edumazet@google.com, pablo@netfilter.org, kadlec@netfilter.org, fw@strlen.de, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, Jason Xing Subject: Re: [PATCH nf-next v2] netfilter: conntrack: avoid sending RST to reply out-of-window skb Message-ID: <20240318201608.GC185808@kernel.org> References: <20240311070550.7438-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240311070550.7438-1-kerneljasonxing@gmail.com> On Mon, Mar 11, 2024 at 03:05:50PM +0800, Jason Xing wrote: > From: Jason Xing > > Supposing we set DNAT policy converting a_port to b_port on the > server at the beginning, the socket is set up by using 4-tuple: > > client_ip:client_port <--> server_ip:b_port > > Then, some strange skbs from client or gateway, say, out-of-window > skbs are eventually sent to the server_ip:a_port (not b_port) > in TCP layer due to netfilter clearing skb->_nfct value in > nf_conntrack_in() function. Why? Because the tcp_in_window() > considers the incoming skb as an invalid skb by returning > NFCT_TCP_INVALID. > > At last, the TCP layer process the out-of-window > skb (client_ip,client_port,server_ip,a_port) and try to look up > such an socket in tcp_v4_rcv(), as we can see, it will fail for sure > because the port is a_port not our expected b_port and then send > back an RST to the client. > > The detailed call graphs go like this: > 1) > nf_conntrack_in() > -> nf_conntrack_handle_packet() > -> nf_conntrack_tcp_packet() > -> tcp_in_window() // tests if the skb is out-of-window > -> return -NF_ACCEPT; > -> skb->_nfct = 0; // if the above line returns a negative value > 2) > tcp_v4_rcv() > -> __inet_lookup_skb() // fails, then jump to no_tcp_socket > -> tcp_v4_send_reset() > > The moment the client receives the RST, it will drop. So the RST > skb doesn't hurt the client (maybe hurt some gateway which cancels > the session when filtering the RST without validating > the sequence because of performance reason). Well, it doesn't > matter. However, we can see many strange RST in flight. > > The key reason why I wrote this patch is that I don't think > the behaviour is expected because the RFC 793 defines this > case: > > "If the connection is in a synchronized state (ESTABLISHED, > FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT), > any unacceptable segment (out of window sequence number or > unacceptible acknowledgment number) must elicit only an empty Not for those following along, it appears that RFC 793 does misspell unacceptable as above. Perhaps spelling was different in 1981 :) > acknowledgment segment containing the current send-sequence number > and an acknowledgment..." > > I think, even we have set DNAT policy, it would be better if the > whole process/behaviour adheres to the original TCP behaviour as > default. > > Suggested-by: Florian Westphal > Signed-off-by: Jason Xing ...