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

From: Daniel Borkmann <[email-masked]>
Date: Fri, 03 Feb 2017 09:25:37 +0100

On 02/03/2017 02:51 AM, Eric Dumazet wrote:
> On Fri, 2017-02-03 at 10:18 +0900, Lorenzo Colitti wrote:
>> On Fri, Feb 3, 2017 at 9:31 AM, Eric Dumazet <[email-masked]> wrote:
>>>> It should be safe to call sock_net_uid on any type of socket
>>>> (including NULL). sk_uid was added to struct sock in 86741ec25462
>>>> ("net: core: Add a UID field to struct sock.")
>>>
>>> But a request socket or a timewait socket do not have this field.
>>>
>>> Daniel point is valid.
>>
>> My bad. Yes.
>>
>> It would definitely be useful to have the UID available in request
>> sockets, and perhaps timewait sockets as well. That could be done by
>> moving the UID to sock_common, or with something along the lines of:
>>
>>   static inline kuid_t sock_net_uid(const struct net *net, const struct sock *sk)
>>   {
>> +       if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
>> +               sk = sk->__sk_common.skc_listener;
>> +       else if (sk && !sk_fullsock(sk))
>> +               sk = NULL;
>> +
>>          return sk ? sk->sk_uid : make_kuid(net->user_ns, 0);
>>   }
>>
>> Any thoughts on which is better?
>
> You could use
>
> if (sk) {
>      sk = sk_to_full_sk(sk);
>      if (sk_fullsock(sk))
>          return sk->sk_uid;
> }

Yeah, if that moves into the sock_net_uid() helper, then you could
remove the sk && sk_fullsock(sk) ? sk : NULL tests from the current
sock_net_uid() call sites such as in tcp code. Maybe then also make
the sock_net_uid() as __always_inline, so that most of the callers
with sock_net_uid(net, NULL) are guaranteed to optimize away their
sk checks at compile time?