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

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Date:   Tue, 7 Jul 2020 23:41:57 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>
Cc:     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 7/7/20 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].

   [0] https://lore.kernel.org/netdev/20190221221356.173485-1-ebiggers@kernel.org/

> Acked-by: Andrii Nakryiko <andriin@...com>
> 
>> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
>> index c66c545e161a..2c6f26670acc 100644
>> --- a/include/linux/bpf-cgroup.h
>> +++ b/include/linux/bpf-cgroup.h
> 
> [...]
>