Re: [PATCH v2] seccomp: add ptrace options for suspend/resume

[Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 06/03, Tycho Andersen wrote:
>
> @@ -556,6 +557,11 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
>  	if (data & ~(unsigned long)PTRACE_O_MASK)
>  		return -EINVAL;
>
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +	if (data & PTRACE_O_SUSPEND_SECCOMP && !may_suspend_seccomp())
> +		return -EPERM;
> +#endif
> +

Well. This -EPERM doesn't look consistent...

if config_enabled(CONFIG_CHECKPOINT_RESTORE) == F, we return success
but PTRACE_O_SUSPEND_SECCOMP has no effect because of another ifdef in
seccomp.

OTOH, if CONFIG_SECCOMP=n, this option has no effect too but we return
-EPERM even.

Also. Suppose that the tracer sets SUSPEND_SECCOMP and then drops
CAP_SYS_ADMIN. After that it can't set or clear other ptrace options.

So if we really want the security checks (I still think we do not ;)
then we should probably check "flags & SUSPEND_SECCOMP" as well.

> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +bool may_suspend_seccomp(void)
> +{
> +	if (!capable(CAP_SYS_ADMIN))
> +		return false;
> +
> +	if (current->seccomp.mode != SECCOMP_MODE_DISABLED)
> +		return false;

Heh. OK, I won't argue with the new check too ;)

Oleg.