Re: /dev/fb* permissions, local DoS

[Michel Dänzer <daenzerm@student.ethz.ch>]

Samu wrote:

> On Sun, Nov 19, 2000 at 06:04:01AM -0900, Ethan Benson wrote:
>
> > does anyone know why debian has /dev/fb* with 622 permissions? 
> >
> > the reason i ask is there is a pretty nasty security problem with
> > this, try the following:
> >
> > cat /dev/urandom > /dev/fb0
> >
> > on my system i get a instant kernel panic (2.2.17 from ftp.kernel.org).
> > since the framebuffer devices are world writable anyone with a shell
> > account can crash the system, not nice. (i have a blue G3 using
> > aty128fb) 
> >
> > what is broken by setting the permissions on all the framebuffer
> > devices to 0600 ?
>
> well with fbtv or fbi there's a line like this 
> (fb = open("/dev/fb0",O_WRONLY,0))

So 0620 might be better, with /dev/fb in group video or a dedicated group.

This is on a SuSE 6.4 system BTW:

crw-rw----   1 root     video     29,   0 Mar 11  2000 /dev/fb0


Michel

--
Earthling Michel Dänzer (MrCooper)  \  CS student and free software enthusiast
Debian GNU/Linux (powerpc,i386) user \   member of XFree86 and the DRI project