netdev - Re: [PATCHv2 net-next 00/10] net: support ipv4 big tcp

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Message-ID: <CANn89iKX6yTPmK6ahxHa6duO1PMn=fFhAXWdYuxNsDkvh8QvLA@mail.gmail.com>
Date:   Tue, 24 Jan 2023 17:34:56 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem@...emloft.net,
        kuba@...nel.org, Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...il.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: [PATCHv2 net-next 00/10] net: support ipv4 big tcp

On Tue, Jan 24, 2023 at 4:51 PM Xin Long <lucien.xin@...il.com> wrote:
>
> On Tue, Jan 24, 2023 at 3:27 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Tue, Jan 24, 2023 at 3:20 AM Xin Long <lucien.xin@...il.com> wrote:
> > >
> > > This is similar to the BIG TCP patchset added by Eric for IPv6:
> > >
> > >   https://lwn.net/Articles/895398/
> > >
> > > Different from IPv6, IPv4 tot_len is 16-bit long only, and IPv4 header
> > > doesn't have exthdrs(options) for the BIG TCP packets' length. To make
> > > it simple, as David and Paolo suggested, we set IPv4 tot_len to 0 to
> > > indicate this might be a BIG TCP packet and use skb->len as the real
> > > IPv4 total length.
> > >
> > > This will work safely, as all BIG TCP packets are GSO/GRO packets and
> > > processed on the same host as they were created; There is no padding
> > > in GSO/GRO packets, and skb->len - network_offset is exactly the IPv4
> > > packet total length; Also, before implementing the feature, all those
> > > places that may get iph tot_len from BIG TCP packets are taken care
> > > with some new APIs:
> > >
> > > Patch 1 adds some APIs for iph tot_len setting and getting, which are
> > > used in all these places where IPv4 BIG TCP packets may reach in Patch
> > > 2-8, and Patch 9 implements this feature and Patch 10 adds a selftest
> > > for it.
> > >
> > > Note that the similar change as in Patch 2-6 are also needed for IPv6
> > > BIG TCP packets, and will be addressed in another patchset.
> > >
> > > The similar performance test is done for IPv4 BIG TCP with 25Gbit NIC
> > > and 1.5K MTU:
> > >
> > > No BIG TCP:
> > > for i in {1..10}; do netperf -t TCP_RR -H 192.168.100.1 -- -r80000,80000 -O MIN_LATENCY,P90_LATENCY,P99_LATENCY,THROUGHPUT|tail -1; done
> > > 168          322          337          3776.49
> > > 143          236          277          4654.67
> > > 128          258          288          4772.83
> > > 171          229          278          4645.77
> > > 175          228          243          4678.93
> > > 149          239          279          4599.86
> > > 164          234          268          4606.94
> > > 155          276          289          4235.82
> > > 180          255          268          4418.95
> > > 168          241          249          4417.82
> > >
> >
> > NACK again
> >
> > You have not addressed my feedback.
> >
> > Given the experimental nature of BIG TCP, we need separate netlink attributes,
> > so that we can selectively enable BIG TCP for IPV6, and not for IPV4.
> >
> That will be some change, and I will try to work on it.
>
> While at it, just try to be clearer, about the fixes for IPv6 BIG TCP
> I mentioned in this patchset. Since skb->len is trustable for GSO TCP
> packets. Are you still not okay with checking the skb_ipv6_pktlen()
> API added to fix them in netfilter/tc/bridge/openvswitch?
>

Are you speaking of length_mt6() ?

Quite frankly I do not think its implementation should care of GSO or anything.

Considering the definition of this thing clearly never thought of
having big packets,
and an overflow was already possible, I do not see how you can fix it
without some hack...

struct xt_length_info {
    __u16 min, max;
    __u8 invert;
};

Something like:

diff --git a/net/netfilter/xt_length.c b/net/netfilter/xt_length.c
index 1873da3a945abbc6e8849e4555b42acdd34cff2d..90eba619cbe1d11f0fdd394f6dfda2b03fa573cd
100644
--- a/net/netfilter/xt_length.c
+++ b/net/netfilter/xt_length.c
@@ -30,8 +30,7 @@ static bool
 length_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 {
        const struct xt_length_info *info = par->matchinfo;
-       const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
-                                sizeof(struct ipv6hdr);
+       u32 pktlen = min_t(u32, skb->len, 65535);

        return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
 }