Bug#336220: xdm: bogus /dev/mem access lead to trouble on arm platforms
On Sun, Aug 19, 2007 at 02:31:49PM +0200, Brice Goglin wrote:
> On Fri, Oct 28, 2005 at 07:47:14PM +0200, Lennert Buytenhek wrote:
> > On arm platforms where physical RAM doesn't start at physical address
> > zero, opening /dev/mem and reading from it causes a kernel oops. This
> > is arguably a kernel bug, but it's still not a very good idea to just
> > start randomly poking around in /dev/mem in search of entropy, which is
> > what xdm does if it can't get entropy elsewhere.
> >
> > (When the kernel is fixed, blindly reading from /dev/mem will simply
> > just fail with EFAULT instead of oopsing. If that will cause xdm to
> > fail, it should really just fail right away if /dev/random doesn't work.)
>
> xdm seems to try /dev/urandom first nowadays (before /dev/random and then
> /dev/mem). I don't whether arm systems have a /dev/urandom, but it seems
> more likely than having a /dev/random.
>
> I don't know which version of xdm you were running when you reported this
> problem (Xorg 6.8.2 was the latest release on 2005/10/28). But it was at
> the same time that the urandom support has been added upstream (in Xorg
> 6.9.99.902 on 2005/10/29).
>
> So please test with a more recent xdm and report back whether it helps.
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