Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

[Oleg Nesterov <oleg@redhat.com>]

On 11/11, Pavel Emelyanov wrote:
>
> Hm, so intrusiveness is your main concern here, I see.

To me, this is important.

> OK, let's assume we go with sysctl setting the last_pid.
>
> One of the major concerns with previous attempts have been - someone creates
> a process with a pid that was in use by some app recently and screws things
> up with pid reuse.

Good point.

> My approach solves this,

Yes. Although, can't resist, in a subtle way (imho). CLONE_CHILD_USEPIDS
stops working after a clone() without this flag.

> how can sysctl handle it? Allowing
> the last_pid change by the CAP_SYA_ADMIN

Yes, when I suggested set_last_pid I assumed that it needs CAP_SYS_ADMIN.

> only is not an option, since people
> are looking forward to non-root restore.

But CLONE_NEWPID needs CAP_SYS_ADMIN too ?

Anyway, I do not pretend I understand the problem space. And probably
it would be more convenient to change the creds before forking some
children with the predefined pids, I do not know.

So yes, I agree, CLONE_CHILD_USEPIDS wins here. Perhaps set_last_pid
needs another sysctl(set_last_pid_allowed)/whatever, or another idea.
Or we should use CLONE_CHILD_USEPIDS ;)

Let me repeat. It is not that I strongly against CLONE_CHILD_USEPIDS
(although yes, I can't say personally I like it very much ;). Just
I am trying to ensure we can't make something more clear/clean/simple,
at least from the kernel pov. Especially because you are trying to
establish the new user-visible API.

Oleg.