netdev - Re: [PATCH bpf-next v4 1/4] bpf: add BPF_CGROUP_INET_SOCK

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Date:   Wed, 8 Jul 2020 01:56:27 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH bpf-next v4 1/4] bpf: add BPF_CGROUP_INET_SOCK_RELEASE
 hook

On 7/8/20 1:43 AM, Stanislav Fomichev wrote:
> On Tue, Jul 7, 2020 at 2:42 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>>
>> On 7/7/20 1:42 AM, Andrii Nakryiko wrote:
>>> On Mon, Jul 6, 2020 at 4:02 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>>>>
>>>> Implement BPF_CGROUP_INET_SOCK_RELEASE hook that triggers
>>>> on inet socket release. It triggers only for userspace
>>>> sockets, the same semantics as existing BPF_CGROUP_INET_SOCK_CREATE.
>>>>
>>>> The only questionable part here is the sock->sk check
>>>> in the inet_release. Looking at the places where we
>>>> do 'sock->sk = NULL', I don't understand how it can race
>>>> with inet_release and why the check is there (it's been
>>>> there since the initial git import). Otherwise, the
>>>> change itself is pretty simple, we add a BPF hook
>>>> to the inet_release and avoid calling it for kernel
>>>> sockets.
>>>>
>>>> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
>>>> ---
>>>>    include/linux/bpf-cgroup.h | 4 ++++
>>>>    include/uapi/linux/bpf.h   | 1 +
>>>>    kernel/bpf/syscall.c       | 3 +++
>>>>    net/core/filter.c          | 1 +
>>>>    net/ipv4/af_inet.c         | 3 +++
>>>>    5 files changed, 12 insertions(+)
>>>>
>>>
>>> Looks good overall, but I have no idea about sock->sk NULL case.
>>
>> +1, looks good & very useful hook. For the sock->sk NULL case here's a related
>> discussion on why it's needed [0].
> Thanks for the pointer! I'll resend a v5 with s/sock/sock_create/ you
> mentioned and will clean up the commit description a bit.

Already fixed up the selftest and a typo in the commit desc there & applied it. Let
me know if you prefer a respin though and I can toss it taking the respin which would
work just as well. :)

Thanks,
Daniel