linux-kernel - Re: [PATCH 1/2] add helper for highmem checks

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Message-ID: <5119786B.9020400@zytor.com>
Date:	Mon, 11 Feb 2013 15:02:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mingo@...nel.org,
	tglx@...utronix.de
Subject: Re: [PATCH 1/2] add helper for highmem checks

On 02/11/2013 03:00 PM, Borislav Petkov wrote:
> On Mon, Feb 11, 2013 at 02:46:43PM -0800, H. Peter Anvin wrote:
>> The X server itself used to do that. Are you saying that wdm is a
>> *privileged process*?
> 
> Nah, it is a simple display manager you start with /etc/init.d/wdm init
> script. Like the other display managers gdm, kdm, etc.
> 
> But it looks like wdm has copied stuff from xdm (from the README):
> 
> "Wdm is a modification of XFree86's xdm package for graphically handling
> authentication and system login. Most of xdm has been preserved (XFree86
> 4.2.1.1) with the Login interface based on a WINGs implementation using
> Tom Rothamel's "external greet" interface (see AUTHORS)."
> 
> And from looking at the part in the source which does the /dev/mem
> accesses, it comes from XFree86's source apparently, this is at the
> beginning of src/wdm/genauth.c:
> 

Oh, it's not a *window manager*, it is a *session manager* (display
manager), and so it runs as root by default.

Plug the damned hole, submit a bug report to Debian to change the
default, and let's be done with it.  That being said, it did flag a real
problem, but what it is doing is dangerous.

	-hpa

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