linux-kernel - Re: questions to planned lock-functionality for vts

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Message-ID: <CANq1E4RYXHQzcxrEZnLBYFN3NvUNHNa+19G96H=cHyX-SeFetw@mail.gmail.com>
Date:	Mon, 23 Mar 2015 13:29:55 +0100
From:	David Herrmann <dh.herrmann@...il.com>
To:	simone.weiss@....de
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	helene.gsaenger@...dium.fau.de, Jiri Slaby <jslaby@...e.cz>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Peter Hurley <peter@...leysoftware.com>,
	Takashi Iwai <tiwai@...e.de>, mark.d.rustad@...el.com,
	Joe Perches <joe@...ches.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-kernel@...cs.fau.de
Subject: Re: questions to planned lock-functionality for vts

Hi

On Mon, Mar 23, 2015 at 11:29 AM,  <simone.weiss@....de> wrote:
>
>> Wait, what's wrong with the existing functionality?
>
> Userspace programms for screensavers can potentially be bypassed
> - if my scrennsaver dies, for example by segfault, my screen is unlocked
> - Redirection is only possible in Kernel, because a vt switch can only
>   be prevented there
> Also it would make the implementation of a Secure-Acess-Key possible
> (could also redirect to VT12)

By moving these calls into the kernel, you don't make them necessarily
fail-safe. This can all be implemented in user-space. By switching to
a dedicated VT (say, VT12) and running VT_SETMODE+VT_PROCESS, you lock
the machine. You can now implement your screensaver. If you run a
spawner-process, you're even safe if your screensaver crashes.

Thanks
David
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