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

[Pavel Emelyanov <xemul@parallels.com>]

>> +int suspend_seccomp(struct task_struct *task)
>> +{
>> +	int ret = -EACCES;
>> +
>> +	spin_lock_irq(&task->sighand->siglock);
>> +
>> +	if (!capable(CAP_SYS_ADMIN))
>> +		goto out;
> 
> I am puzzled ;) Why do we need ->siglock? And even if we need it, why
> we can't check CAP_SYS_ADMIN lockless?
> 
> And I am not sure I understand why do we need the additional security
> check, but I leave this to you and Andy.
> 
> If you have the rights to trace this task, then you can do anything
> the tracee could do without the filtering.

I think _this_ check is required, otherwise the seccomp-ed task (in
filtered mode) fork-s a child, then this child ptrace-attach to parent
(allowed) then suspend its seccomd. And -- we have unpriviledged process 
de-seccomped.

-- Pavel