netdev - Re: [PATCH net] tcp: add proper TS val into RST packets

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Message-ID: <CAK6E8=eJfmZV_O14JqucQD4LD+OCybhB1D+PV2giz-Jmpph3qA@mail.gmail.com>
Date:	Wed, 23 Sep 2015 13:36:21 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] tcp: add proper TS val into RST packets

On Wed, Sep 23, 2015 at 1:30 PM, Neal Cardwell <ncardwell@...gle.com> wrote:
>
> On Wed, Sep 23, 2015 at 4:19 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > RST packets sent on behalf of TCP connections with TS option (RFC 7323
> > TCP timestamps) have incorrect TS val (set to 0), but correct TS ecr.
> >
> > A > B: Flags [S], seq 0, win 65535, options [mss 1000,nop,nop,TS val 100 ecr 0], length 0
> > B > A: Flags [S.], seq 2444755794, ack 1, win 28960, options [mss 1460,nop,nop,TS val 7264344 ecr 100], length 0
> > A > B: Flags [.], ack 1, win 65535, options [nop,nop,TS val 110 ecr 7264344], length 0
> >
> > B > A: Flags [R.], seq 1, ack 1, win 28960, options [nop,nop,TS val 0 ecr 110], length 0
> >
> > We need to call skb_mstamp_get() to get proper TS val,
> > derived from skb->skb_mstamp
> >
> > Note that RFC 1323 was advocating to not send TS option in RST segment,
> > but RFC 7323 recommends the opposite :
> >
> >   Once TSopt has been successfully negotiated, that is both <SYN> and
> >   <SYN,ACK> contain TSopt, the TSopt MUST be sent in every non-<RST>
> >   segment for the duration of the connection, and SHOULD be sent in an
> >   <RST> segment (see Section 5.2 for details)
Nice comment. I think it's worth adding why we choose not to follow
RFC7323 sec 5.2 recommendation on setting TSval to 0?


>
> >
> > Fixes: 7faee5c0d514 ("tcp: remove TCP_SKB_CB(skb)->when")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > ---
>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
>
> Thanks, Eric!
>
> neal
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