netdev - Re: [PATCH net-next] tcp: be less liberal in tsecr received while in SYN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iLZSO+Swf78jV0mc9jLUFLiqOtcjbTWsoYmdr=jn0SUxg@mail.gmail.com>
Date: Tue, 25 Feb 2025 18:11:31 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Simon Horman <horms@...nel.org>, Florian Westphal <fw@...len.de>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Jakub Kicinski <kuba@...nel.org>, 
	Yong-Hao Zou <yonghaoz1994@...il.com>, "David S . Miller" <davem@...emloft.net>, 
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: be less liberal in tsecr received while in
 SYN_RECV state

On Tue, Feb 25, 2025 at 5:56 PM Matthieu Baerts <matttbe@...nel.org> wrote:
>
> Hi Eric,
>
> On 25/02/2025 11:51, Eric Dumazet wrote:
> > On Tue, Feb 25, 2025 at 11:48 AM Matthieu Baerts <matttbe@...nel.org> wrote:
> >>
> >> On 25/02/2025 11:42, Eric Dumazet wrote:
> >>> On Tue, Feb 25, 2025 at 11:39 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >>>>
> >>>
> >>>>
> >>>> Yes, this would be it :
> >>>>
> >>>> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> >>>> index 728bce01ccd3ddb1f374fa96b86434a415dbe2cb..3555567ba4fb1ccd5c5921e39d11ff08f1d0cafd
> >>>> 100644
> >>>> --- a/net/ipv4/tcp_timer.c
> >>>> +++ b/net/ipv4/tcp_timer.c
> >>>> @@ -477,8 +477,8 @@ static void tcp_fastopen_synack_timer(struct sock
> >>>> *sk, struct request_sock *req)
> >>>>          * regular retransmit because if the child socket has been accepted
> >>>>          * it's not good to give up too easily.
> >>>>          */
> >>>> -       inet_rtx_syn_ack(sk, req);
> >>>>         req->num_timeout++;
> >>>> +       inet_rtx_syn_ack(sk, req);
> >>>>         tcp_update_rto_stats(sk);
> >>>>         if (!tp->retrans_stamp)
> >>>>                 tp->retrans_stamp = tcp_time_stamp_ts(tp);
> >>>
> >>> Obviously, I need to refine the patch and send a V2 later.
> >>
> >> Sorry, I still have the issue with this modification. I also checked
> >> with the previous patch, just to be sure, but the problem is still there
> >> as well.
> >
> > I said "req->num_timeout" is not updated where I thought it was.
>
> I think that in case of SYN+ACK retransmission, req->num_timeout is
> incremented after tcp_synack_options():
>
>   reqsk_timer_handler()
>   --> inet_rtx_syn_ack()
>     --> tcp_rtx_synack()
>       --> tcp_v6_send_synack()
>         --> tcp_make_synack()
>           --> tcp_synack_options()
>   then: req->num_timeout++
>
> > Look at all the places were req->num_timeout or req->num_retrans are
> > set/changed.... this will give you some indications.
>
> I'm probably missing something obvious, but if the goal is to set
> snt_tsval_first only the first time, why can we not simply set
>
>   tcp_rsk(req)->snt_tsval_first = 0;
>
> in tcp_conn_request(), and only set it to tsval in tcp_synack_options()
> when it is 0? Something like that:
>
>
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index 217a8747a79b..26b3daa5efd2 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -7249,6 +7249,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
> >         tcp_rsk(req)->af_specific = af_ops;
> >         tcp_rsk(req)->ts_off = 0;
> >         tcp_rsk(req)->req_usec_ts = false;
> > +       tcp_rsk(req)->snt_tsval_first = 0;
> >  #if IS_ENABLED(CONFIG_MPTCP)
> >         tcp_rsk(req)->is_mptcp = 0;
> >  #endif
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> > index 485ca131091e..020c624532d7 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -943,7 +943,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
> >                 opts->options |= OPTION_TS;
> >                 opts->tsval = tcp_skb_timestamp_ts(tcp_rsk(req)->req_usec_ts, skb) +
> >                               tcp_rsk(req)->ts_off;
> > -               if (!req->num_timeout)
> > +               if (!tcp_rsk(req)->snt_tsval_first)
> >                         tcp_rsk(req)->snt_tsval_first = opts->tsval;
> >                 WRITE_ONCE(tcp_rsk(req)->snt_tsval_last, opts->tsval);
> >                 opts->tsecr = READ_ONCE(req->ts_recent)
>
>
> Or is the goal to update this field as long as the timeout didn't fire?
> In this case maybe req->num_timeout should be updated before calling
> inet_rtx_syn_ack() in reqsk_timer_handler(), no?
>
> > Do not worry, I will make sure V2 is fine.
>
> I don't doubt about that, thank you! :)

I can see you are super excited to see this patch landing ;)

I sent the V2, after running all my tests.