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

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Date:	Tue, 2 Jun 2015 22:02:10 +0300
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Tycho Andersen <tycho.andersen@...onical.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-api@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Roland McGrath <roland@...k.frob.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [PATCH] seccomp: add ptrace commands for suspend/resume


>> +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

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