Subject: Re: [PATCH net-next 14/16] net: Add sk_bind_dev_if to task_struct

From: David Ahern <[email-masked]>
Date: Tue, 28 Jul 2015 10:11:13 -0600

On 7/28/15 9:25 AM, Andy Lutomirski wrote:
> On Jul 27, 2015 11:33 AM, "David Ahern" <[email-masked]> wrote:
>>
>> Allow tasks to have a default device index for binding sockets. If set
>> the value is passed to all AF_INET/AF_INET6 sockets when they are created.
>>
>
> This is not intended to be a review of the concept.  I haven't thought
> about whether the concept is a good idea, broken by design, or
> whatever.  FWIW, if this were added to the kernel and didn't require
> excessive privilege, I'd probably use it.  (I still don't really
> understand why binding to a device requires privilege in the first
> place, but, again, I haven't thought about it very much.)

The intent here is to restrict a task to only sending and receiving 
packets from a single network device. The device can be single ethernet 
interface, a stacked device (e.g, bond) or in our case a VRF device 
which restricts a task to interfaces (and hence network paths) 
associated with the VRF.

>
>> +#ifdef CONFIG_NET
>> +       case PR_SET_SK_BIND_DEV_IF:
>> +       {
>> +               struct net_device *dev;
>> +               int idx = (int) arg2;
>> +
>> +               if (!capable(CAP_NET_ADMIN))
>> +                       return -EPERM;
>> +
>
> Can you either use ns_capable or add a comment as to why not?

will do.

>
> Also, please return -EINVAL if unused args are nonzero.

ok.

>
>> +               if (idx) {
>> +                       dev = dev_get_by_index(me->nsproxy->net_ns, idx);
>> +                       if (!dev)
>> +                               return -EINVAL;
>> +                       dev_put(dev);
>> +               }
>> +               me->sk_bind_dev_if = idx;
>> +               break;
>> +       }
>> +       case PR_GET_SK_BIND_DEV_IF:
>> +       {
>> +               struct task_struct *tsk;
>> +               int sk_bind_dev_if = -EINVAL;
>> +
>> +               rcu_read_lock();
>> +               tsk = find_task_by_vpid(arg2);
>> +               if (tsk)
>> +                       sk_bind_dev_if = tsk->sk_bind_dev_if;
>
> Why do you support different tasks here?  Could this use proc instead?

In this case we want to allow a separate process to determine if a task 
is restricted to a device.

>
> The same -EINVAL issue applies.
>
> Also, I think you need to hook setns and unshare to do something
> reasonable when the task is bound to a device.

ack on both.

Thanks for the review,
David