netdev - Re: [PATCH net-next] tcp: do not allow to connect with the four-tuple symmetry socket

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Message-ID: <CAL+tcoDDXT4wBQK0akpg4FR+COfZ7dztz5GcWp6ah68nbvwzTg@mail.gmail.com>
Date: Sun, 18 Aug 2024 21:50:51 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, ncardwell@...gle.com, dima@...sta.com, 
	0x7f454c46@...il.com
Cc: netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next] tcp: do not allow to connect with the four-tuple
 symmetry socket

On Sun, Aug 18, 2024 at 1:16 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> On Sun, Aug 18, 2024 at 12:25 PM Jason Xing <kerneljasonxing@...il.com> wrote:
> >
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Four-tuple symmetry here means the socket has the same remote/local
> > port and ipaddr, like this, 127.0.0.1:8000 -> 127.0.0.1:8000.
> > $ ss -nat | grep 8000
> > ESTAB      0      0          127.0.0.1:8000       127.0.0.1:8000

Thanks to the failed tests appearing in patchwork, now I'm aware of
the technical term called "self-connection" in English to describe
this case. I will update accordingly the title, body messages,
function name by introducing "self-connection" words like this in the
next submission.

Following this clue, I saw many reports happening in these years, like
[1][2]. Users are often astonished about this phenomenon and lost and
have to find various ways to workaround it. Since, in my opinion, the
self-connection doesn't have any advantage and usefulness, why not
avoid it in the kernel? Could networking experts enlighten me? Thanks.

+ Dmitry
Hello Dmitry, do you know why the self-connect_ipv4/6 was introduced
in the selftests which the patch I wrote failed? Thanks.

[1]: https://adil.medium.com/what-is-tcp-self-connect-issue-be7d7b5f9f59
[2]: https://stackoverflow.com/questions/5139808/tcp-simultaneous-open-and-self-connect-prevention

Thanks,
Jason