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 21:06:47 +0900
From:   Lorenzo Colitti <lorenzo@...gle.com>
To:     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>,
        Alexei Starovoitov <ast@...com>,
        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 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);