[mythtv-users] Re: Suid root, but mythtv complains that it isn't.

[Tom Hughes]

In message <41E13BCA.6020606 at ties.org>
          Doug Larrick <doug at ties.org> wrote:

> Tom Hughes wrote:
> > The problem appears to be that the kernel now implements setuid
> > properly so that it changes the UID of the process rather than just
> > the current thread so it isn't possible to have a privileged thread
> > anymore.
> > 
> > Basically the whole scheme only worked because threads on linux
> > are effectively processes at the kernel level and certain system
> > calls didn't properly take account of that, including setuid.
> 
> Good to know.  What kernel is this?  Matt Zimmerman (rightly) complains
> about the security of the current implementation, as well.

It's the standard FC3 one, the 1.681 build of 2.6.9 at the moment.

I have a test program that check the setuid behaviour and on
a RedHat 9 box only the thread that calls setuid changes but
on an FC3 box both threads change. I haven't tried it on anything
else yet.

> I have a replacement scheme in mind that creates a realtime-priority
> thread for playback at startup before dropping privs, and then reuses
> that thread for all playback.  I just need to find the time to work on it.

That would be the obvious alternative.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/