netdev - Re: [PATCH net-next v7 2/3] Add a eBPF helper function to retrieve socket uid

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Date:   Wed, 22 Mar 2017 12:25:30 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Lorenzo Colitti <lorenzo@...gle.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     Chenbo Feng <chenbofeng.kernel@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Chenbo Feng <fengc@...gle.com>
Subject: Re: [PATCH net-next v7 2/3] Add a eBPF helper function to retrieve
 socket uid

On 3/22/17 5:06 AM, Lorenzo Colitti wrote:
> On Wed, Mar 22, 2017 at 8:09 PM, Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
>>> +       if (!sk || !sk_fullsock(sk))
>>> +               return overflowuid;
>>> +       kuid = sock_net_uid(sock_net(sk), sk);
>>> +       return from_kuid_munged(&init_user_ns, kuid);
>>
>> Ideally, this would be the user namespace relative to the BPF program.
>
> What about sock_net(sk)->user_ns? We've already matched a socket, and
> it's guaranteed to be a full socket and non-NULL (otherwise we've
> already returned overflowuid), so it seems like the most correct
> namespace to use is the one of the socket we've matched. Given that sk
> is non-NULL, sock_net_uid just returns sk->sk_uid, so I think you can
> just write this as:
>
> if (!sk || !sk_fullsock(sk))
>         return overflowuid;
> return from_kuid_munged(sock_net(sk)->user_ns, sk->uid);
>

makes sense to me.