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Date:   Fri, 1 May 2020 15:29:42 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Andrey Ignatov <rdna@...com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3] bpf: bpf_{g,s}etsockopt for struct bpf_sock_addr

On Fri, May 1, 2020 at 3:16 PM Andrey Ignatov <rdna@...com> wrote:
>
> Stanislav Fomichev <sdf@...gle.com> [Fri, 2020-05-01 15:07 -0700]:
> > On Fri, May 1, 2020 at 2:52 PM Andrey Ignatov <rdna@...com> wrote:
> > >
> > > Stanislav Fomichev <sdf@...gle.com> [Thu, 2020-04-30 16:32 -0700]:
> > > > Currently, bpf_getsockopt and bpf_setsockopt helpers operate on the
> > > > 'struct bpf_sock_ops' context in BPF_PROG_TYPE_SOCK_OPS program.
> > > > Let's generalize them and make them available for 'struct bpf_sock_addr'.
> > > > That way, in the future, we can allow those helpers in more places.
> > > >
> > > > As an example, let's expose those 'struct bpf_sock_addr' based helpers to
> > > > BPF_CGROUP_INET{4,6}_CONNECT hooks. That way we can override CC before the
> > > > connection is made.
> > > >
> > > > v3:
> > > > * Expose custom helpers for bpf_sock_addr context instead of doing
> > > >   generic bpf_sock argument (as suggested by Daniel). Even with
> > > >   try_socket_lock that doesn't sleep we have a problem where context sk
> > > >   is already locked and socket lock is non-nestable.
> > > >
> > > > v2:
> > > > * s/BPF_PROG_TYPE_CGROUP_SOCKOPT/BPF_PROG_TYPE_SOCK_OPS/
> > > >
> > > > Cc: John Fastabend <john.fastabend@...il.com>
> > > > Cc: Martin KaFai Lau <kafai@...com>
> > > > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > >
> > > ...
> > >
> > > >  SEC("cgroup/connect4")
> > > >  int connect_v4_prog(struct bpf_sock_addr *ctx)
> > > >  {
> > > > @@ -66,6 +108,10 @@ int connect_v4_prog(struct bpf_sock_addr *ctx)
> > > >
> > > >       bpf_sk_release(sk);
> > > >
> > > > +     /* Rewrite congestion control. */
> > > > +     if (ctx->type == SOCK_STREAM && set_cc(ctx))
> > > > +             return 0;
> > >
> > > Hi Stas,
> > >
> > > This new check breaks one of tests in test_sock_addr:
> > >
> > >         root@...h-fb-vm1:/home/rdna/bpf-next/tools/testing/selftests/bpf ./test_sock_addr.sh
> > >         ...
> > >         (test_sock_addr.c:1199: errno: Operation not permitted) Fail to connect to server
> > >         Test case: connect4: rewrite IP & TCP port .. [FAIL]
> > >         ...
> > >         Summary: 34 PASSED, 1 FAILED
> > >
> > > What the test does is it sets up TCPv4 server:
> > >
> > >         [pid   386] socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 6
> > >         [pid   386] bind(6, {sa_family=AF_INET, sin_port=htons(4444), sin_addr=inet_addr("127.0.0.1")}, 128) = 0
> > >         [pid   386] listen(6, 128)              = 0
> > >
> > > Then tries to connect to a fake IPv4:port and this connect4 program
> > > should redirect it to that TCP server, but only if every field in
> > > context has expected value.
> > >
> > > But after that commit program started denying the connect:
> > >
> > >         [pid   386] socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 7
> > >         [pid   386] connect(7, {sa_family=AF_INET, sin_port=htons(4040), sin_addr=inet_addr("192.168.1.254")}, 128) = -1 EPERM (Operation not permitted)
> > >         (test_sock_addr.c:1201: errno: Operation not permitted) Fail to connect to server
> > >         Test case: connect4: rewrite IP & TCP port .. [FAIL]
> > >
> > > I verified that commenting out this new `if` fixes the problem, but
> > > haven't spent time root-causing it. Could you please look at it?
> > Could you please confirm that you have CONFIG_TCP_CONG_DCTCP=y in your kernel
> > config? (I've added it to tools/testing/selftests/bpf/config)
> > The test is now flipping CC to dctcp and back to default cubic. It can
> > fail if dctcp is not compiled in.
>
> Right. Martin asked same question and indeed my testing VM didn't have
> dctcp enabled. With dctcp enabled it works fine.
>
> I'm totally fine to keep dctcp enabled in my config or start using
> tools/testing/selftests/bpf/config (I've always used my own config).
>
> Another options can be to switch from dctcp to more widely-used reno in
> the program (I tested, this works as well), or even check
> net/ipv4/tcp_available_congestion_control and use a pair of whatever cc
> available there, but up to you / BPF mainteiners really, as I said I'm
> personally fine to just enable dctcp.
Hm, good point, reno is always compiled in, I didn't think about it.
Let me prepare a patch to do s/dctcp/reno/ in that test, thanks!

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