netdev - Re: [PATCH net-next 09/10] netfilter: get ipv6 pktlen properly in length

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Message-ID: <CANn89i+OeD6Tmj0eyn=NK8M6syxKEQYLQfv4KUMmMGBh98YKyw@mail.gmail.com>
Date:   Mon, 16 Jan 2023 21:37:08 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     David Ahern <dsahern@...il.com>,
        network dev <netdev@...r.kernel.org>, davem@...emloft.net,
        kuba@...nel.org, Paolo Abeni <pabeni@...hat.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Pravin B Shelar <pshelar@....org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Ilya Maximets <i.maximets@....org>,
        Aaron Conole <aconole@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Paul Moore <paul@...l-moore.com>,
        Guillaume Nault <gnault@...hat.com>
Subject: Re: [PATCH net-next 09/10] netfilter: get ipv6 pktlen properly in length_mt6

On Mon, Jan 16, 2023 at 8:10 PM Xin Long <lucien.xin@...il.com> wrote:
>
> On Mon, Jan 16, 2023 at 11:02 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Mon, Jan 16, 2023 at 4:08 PM David Ahern <dsahern@...il.com> wrote:
> > >
> >
> > > not sure why you think it would not be detected. Today's model for gro
> > > sets tot_len based on skb->len. There is an inherent trust that the
> > > user's of the gro API set the length correctly. If it is not, the
> > > payload to userspace would ultimately be non-sense and hence detectable.
> >
> > Only if you use some kind of upper protocol adding message integrity
> > verification.
> >
> > > >
> > > > As you said, user space sniffing packets now have to guess what is the
> > > > intent, instead of headers carrying all the needed information
> > > > that can be fully validated by parsers.
> > >
> > > This is a solveable problem within the packet socket API, and the entire
> > > thing is opt-in. If a user's tcpdump / packet capture program is out of
> > > date and does not support the new API for large packets, then that user
> > > does not have to enable large GRO/TSO.
> >
> > I do not see this being solved yet.
> I think it's common that we add a feature that is disabled by
> default in the kernel if the userspace might not support it.

One critical feature for us is the ability to restrict packet capture
to the headers only.

Privacy is a key requirement.

https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=3e5289d5e3f98b7b5b8cac32e9e5a7004c067436

So please make sure that packet captures truncated to headers will
still be understood by tcpdump


>
> >
> > We have enabled BIG TCP only for IPv6, we do not want the same to
> > magically be enabled for ipv4
> > when a new kernel is deployed.
> >
> > Make sure that IPV4 BIG TCP is guarded by a separate tunable.
> I can understand this.
>
> Thanks.