Re: [PATCH v1 bpf-next 00/11] bpf: tcp: Add SYN Cookie generation/validation SOCK_OPS hooks.

From: Eric Dumazet <edumazet@google.com>
To: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>,
	andrii@kernel.org, ast@kernel.org,  bpf@vger.kernel.org,
	daniel@iogearbox.net, davem@davemloft.net,  dsahern@kernel.org,
	haoluo@google.com, john.fastabend@gmail.com,  jolsa@kernel.org,
	kpsingh@kernel.org, kuba@kernel.org, kuni1840@gmail.com,
	 mykolal@fb.com, netdev@vger.kernel.org, pabeni@redhat.com,
	sdf@google.com,  song@kernel.org, yonghong.song@linux.dev
Subject: Re: [PATCH v1 bpf-next 00/11] bpf: tcp: Add SYN Cookie generation/validation SOCK_OPS hooks.
Date: Wed, 18 Oct 2023 10:02:51 +0200	[thread overview]
Message-ID: <CANn89iLZDvqrGy9UJ39a49O3NLT74r+5FXfh7u3SxSSm60BJmA@mail.gmail.com> (raw)
In-Reply-To: <469fd0e9-686f-f1dc-cb45-6c50ff126ccf@linux.dev>

On Wed, Oct 18, 2023 at 8:19 AM Martin KaFai Lau <martin.lau@linux.dev> wrote:
>
> On 10/17/23 9:48 AM, Kuniyuki Iwashima wrote:
> > From: Martin KaFai Lau <martin.lau@linux.dev>
> > Date: Mon, 16 Oct 2023 22:53:15 -0700
> >> On 10/13/23 3:04 PM, Kuniyuki Iwashima wrote:
> >>> Under SYN Flood, the TCP stack generates SYN Cookie to remain stateless
> >>> After 3WHS, the proxy restores SYN and forwards it and ACK to the backend
> >>> server.  Our kernel module works at Netfilter input/output hooks and first
> >>> feeds SYN to the TCP stack to initiate 3WHS.  When the module is triggered
> >>> for SYN+ACK, it looks up the corresponding request socket and overwrites
> >>> tcp_rsk(req)->snt_isn with the proxy's cookie.  Then, the module can
> >>> complete 3WHS with the original ACK as is.
> >>
> >> Does the current kernel module also use the timestamp bits differently?
> >> (something like patch 8 and patch 10 trying to do)
> >
> > Our SYN Proxy uses TS as is.  The proxy nodes generate a random number
> > if TS is in SYN.
> >
> > But I thought someone would suggest making TS available so that we can
> > mock the default behaviour at least, and it would be more acceptable.
> >
> > The selftest uses TS just to strengthen security by validating 32-bits
> > hash.  Dropping a part of hash makes collision easier to happen, but
> > 24-bits were sufficient for us to reduce SYN flood to the managable
> > level at the backend.
>
> While enabling bpf to customize the syncookie (and timestamp), I want to explore
> where can this also be done other than at the tcp layer.
>
> Have you thought about directly sending the SYNACK back at a lower layer like
> tc/xdp after receiving the SYN? There are already bpf_tcp_{gen,check}_syncookie
> helper that allows to do this for the performance reason to absorb synflood. It
> will be natural to extend it to handle the customized syncookie also.
>
> I think it should already be doable to send a SYNACK back with customized
> syncookie (and timestamp) at tc/xdp today.
>
> When ack is received, the prog@tc/xdp can verify the cookie. It will probably
> need some new kfuncs to create the ireq and queue the child socket. The bpf prog
> can change the ireq->{snd_wscale, sack_ok...} if needed. The details of the
> kfuncs need some more thoughts. I think most of the bpf-side infra is ready,
> e.g. acquire/release/ref-tracking...etc.
>

I think I mostly agree with this.

I am rebasing  a patch adding usec resolution to TCP TS,
that we used for about 10 years at Google, because it is time to upstream it.

I am worried about more changes/conflicts caused by Kuniyuki patch set...