Bug#564079: Is this really a screensaver issue?
Lars Olav Dybsjord
larsod at ping.uio.no
Tue Jan 26 17:11:38 UTC 2010
On 2010-01-26 17:31, Josselin Mouette wrote:
> Le mardi 26 janvier 2010 à 16:19 +0100, Guido Günther a écrit :
> > > True, but this one is trivial to exploit and is also fairly easy to prevent so
> > > why stick with it?
> > I can only agree here. procps should at least get a:
> >
> > sys.kernel.sysrq = 0
>
> It’s only a workaround, and it’s a bit too much to disable all SysRq
> since other SysRq combinations are not a security threat. However we
> could ship this in the gnome-screensaver/xscreensaver packages if there
> is no other solution. This would make the obvious and immediate security
> issue go away. Simultaneously, we can forward the issue upstream so that
> they can work on an appropriate X11 extension as suggested by Bastian.
Another solution could be to let the screensaver set /proc/self/oom_adj to
-17 to disable the possibility of this process beeing killed by the
oom-killer.
(linux/Documentation/filesystems/proc.txt)
>
> > Safest would be to make the kernel default to off though (the user can
> > still reenable this via procps) since there's otherwise still a race
> > until /etc/init.d/procps starts.
>
> I don’t think this race condition is relevant. The only thing that can
> protect you from someone who has access to the console at boot time is
> to encrypt your data. The screensaver’s lock is here to prevent the data
> from being accessed without a reboot.
>
> Cheers,
> --
> .''`. Josselin Mouette
> : :' :
> `. `' “A handshake with whitnesses is the same
> `- as a signed contact.” -- Jörg Schilling
>
Lars Olav Dybsjord
larsod at ping.uio.no
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