Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

[Oleg Nesterov <oleg@redhat.com>]

On 01/12, Steven Rostedt wrote:
>
> On Thu, 2012-01-12 at 17:14 +0100, Oleg Nesterov wrote:
>
> > May be this needs something like LSM_UNSAFE_SECCOMP, or perhaps
> > cap_bprm_set_creds() should take seccomp.mode == 2 into account, I dunno.
> >
> > OTOH, currently seccomp.mode == 1 doesn't allow to exec at all.
>
> I've never used seccomp, so I admit I'm totally ignorant on this topic.

me too ;)

> But looking at seccomp from the outside, the biggest advantage to this
> would be the ability for normal processes to be able to limit tasks it
> kicks off. If I want to run a task in a sandbox, I don't want to be root
> to do so.
>
> I guess a web browser doesn't perform an exec to run java programs. But
> it would be nice if I could execute something from the command line that
> I could run in a sand box.
>
> What's the problem with making sure that the setuid isn't set before
> doing an execv? Only fail when setuid (or some other magic) is enabled
> on the file being exec'd.

I agree. That is why I mentioned LSM_UNSAFE_SECCOMP/cap_bprm_set_creds.
Just I do not know what would be the most simple/clean way to do this.


And in any case I agree that the current seccomp_check_exec() looks
strange. Btw, it does
{
	if (current->seccomp.mode != 2)
		return 0;
	/* We can rely on the task refcount for the filter. */
	if (!current->seccomp.filter)
		return -EPERM;

How it is possible to have seccomp.filter == NULL with mode == 2?

Oleg.