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From: Paolo Abeni <pabeni@redhat.com>
To: Mat Martineau <mathew.j.martineau@linux.intel.com>,
	Jianguo Wu <wujianguo106@163.com>
Cc: mptcp@lists.linux.dev, fw@strlen.de
Subject: Re: [PATCH v5 4/4] mptcp: avoid processing packet if a subflow reset
Date: Wed, 23 Jun 2021 11:48:01 +0200	[thread overview]
Message-ID: <1ac0561c290bf87aa54277bc6b458a859b8ff080.camel@redhat.com> (raw)
In-Reply-To: <2024b917-84de-4dea-2244-5dce7a7f2495@linux.intel.com>

On Tue, 2021-06-22 at 17:00 -0700, Mat Martineau wrote:
> On Mon, 21 Jun 2021, Jianguo Wu wrote:
> 
> > Hi Mat,
> > 
> > On 2021/6/19 8:19, Mat Martineau wrote:
> > > On Wed, 16 Jun 2021, wujianguo106@163.com wrote:
> > > 
> > > > From: Jianguo Wu <wujianguo@chinatelecom.cn>
> > > > 
> > > > If check_fully_established() causes a subflow reset, it should not
> > > > continue to process the packet in tcp_data_queue().
> > > > 
> > > > setting:
> > > >     TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
> > > > 
> > > > so that the following check will drop the pkt in
> > > > tcp_data_queue():
> > > >  if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
> > > >     __kfree_skb(skb);
> > > >     return;
> > > >  }
> > > > 
> > > > Fixes: d582484726c4 ("mptcp: fix fallback for MP_JOIN subflows")
> > > > Signed-off-by: Jianguo Wu <wujianguo@chinatelecom.cn>
> > > > ---
> > > > net/mptcp/options.c | 6 ++++++
> > > > 1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/net/mptcp/options.c b/net/mptcp/options.c
> > > > index 1aec01686c1a..be435c5421cd 100644
> > > > --- a/net/mptcp/options.c
> > > > +++ b/net/mptcp/options.c
> > > > @@ -926,6 +926,12 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
> > > >     return true;
> > > > 
> > > > reset:
> > > > +    /* If a subflow is reset, the packet should not continue to be
> > > > +     * processed in tcp_data_queue(), so setting: end_seq = seq,
> > > > +     * then tcp_data_queue() will drop the packet.
> > > > +     */
> > > > +    TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
> > > > +
> > > 
> > > This does have the desired effect when mptcp_incoming_options() is 
> > > called from tcp_data_queue(), but mptcp_incoming_options() is also 
> > > called from tcp_reset() and tcp_rcv_state_process(). The other callers 
> > > appear to tolerate the sequence number modification.
> > > 
> > > I think it would be clearer to either add a return value or output 
> > > parameter to mptcp_incoming_options() to explicitly tell the caller 
> > > that a reset has been sent and tcp_done() called. Then it would be 
> > > clearer in tcp_data_queue() that the packet is being discarded due to 
> > > mptcp header content.
> > > 
> > 
> > If a reset has been sent and tcp_done() called in 
> > check_fully_established(), the sk_state will be TCP_CLOSE, how about 
> > just do (sk_state == TCP_CLOSE) check in tcp_data_queue() as it did in 
> > the V1 of this patch?
> 
> Oh, I see now that Paolo suggested the the end_seq assignment in order to 
> only modify MPTCP code.
> 
> I still think it's better to make it clear that we're discarding a packet 
> due to the mptcp headers - using the existing sequence check (intended to 
> detect acks) in tcp_data_queue() seems sneaky to me.
> 
> Something like
> 
> if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
>  	__kfree_skb(skb);
>  	return;
> }
> 
> seems both compact and clear. Does that seem ok Paolo?

Uhmmm... we need to touch every mptcp_incoming_options() call site, and
in tcp_reset() the above chunk looks a bit strange to me. Probably we
could just ignore the mptcp_incoming_options() return value there. 

Otherwise no big objections - not sure about upstream ;)

Cheers,

Paolo


  reply	other threads:[~2021-06-23  9:48 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16 10:49 [PATCH v5 0/4] Fix some mptcp syncookie process bugs wujianguo106
2021-06-16 10:49 ` [PATCH v5 1/4] mptcp: fix warning in __skb_flow_dissect() when do syn cookie for subflow join wujianguo106
2021-06-18 22:40   ` Mat Martineau
2021-06-21  6:14     ` Jianguo Wu
2021-06-21 10:09       ` Jianguo Wu
2021-06-22 23:38         ` Mat Martineau
2021-06-16 10:49 ` [PATCH v5 2/4] mptcp: remove redundant req destruct in subflow_check_req() wujianguo106
2021-06-16 10:49 ` [PATCH v5 3/4] mptcp: fix syncookie process if mptcp can not_accept new subflow wujianguo106
2021-06-18 23:19   ` Mat Martineau
2021-06-21  6:24     ` Jianguo Wu
2021-06-24  2:08       ` Jianguo Wu
2021-06-24 22:36         ` Mat Martineau
2021-06-16 10:49 ` [PATCH v5 4/4] mptcp: avoid processing packet if a subflow reset wujianguo106
2021-06-19  0:19   ` Mat Martineau
2021-06-21  6:35     ` Jianguo Wu
2021-06-23  0:00       ` Mat Martineau
2021-06-23  9:48         ` Paolo Abeni [this message]
2021-06-24  1:57           ` Jianguo Wu
2021-06-24 10:02             ` Paolo Abeni
2021-06-24 22:38               ` Mat Martineau
2021-06-25  0:51               ` Jianguo Wu
2021-06-19  0:26 ` [PATCH v5 0/4] Fix some mptcp syncookie process bugs Mat Martineau
2021-06-21  6:39   ` Jianguo Wu
2021-06-23  0:07     ` Mat Martineau

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