Re: CVE request -- coreutils -- tty hijacking possible in "su" via TIOCSTI ioctl

[Ludwig Nussel <ludwig.nussel () suse de>]

Josh Bressers wrote:
> ----- Original Message -----
> > Jan Lieskovsky wrote:
> > > Hello Josh, Steve, vendors,
> > >
> > >    based on Debian BTS report:
> > >    [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=628843
> > >        (first CVE-2011-XXYY required for Debian case)
> > >
> > > looked more into original report:
> > > [2] https://bugzilla.redhat.com/show_bug.cgi?id=173008
> > >
> > > and the first paragraph of [2] suggests:
> > > "When starting a program via "su - user -c program" the user session
> > > can escape to the parent session by using the TIOCSTI ioctl to push
> > > characters into the input buffer. This allows for example a non-root
> > > session to push "chmod 666 /etc/shadow" or similarly bad commands
> > > into
> > > the input buffer such that after the end of the session they are
> > > executed."
> > >
> > > this should get a CVE-2005-YYZZ CVE id.
> > >
> > > Could you allocate these?
> >
> > ping! :-)
>
> I'm not sure if this should get two IDs. It's really one issue, which isn't
> actually fixed in su.
>
> The fundamental issue is that tools like su and sudo keep the tty open.
> The patch in question closes the tty for the case of su -c, but not for
> just running su by itself. It is incomplete.

I'm not worried too much about the interactive su case really. The 
usual direction there is user->root, not the other way around I 
suppose. "su -c" might be used by (%post) scripts though as seen 
with ikiwiki.
Wrt non-interactive sudo I'm not sure. It's less likely to be used 
by sane packages at least as it's behavior is rather unpredictable 
due to it's many configuration options.

> It should get a 2005 ID at the very least, MITRE will have to do that.
> Perhaps two 2005 IDs? One for the issue, the second for the incomplete fix
> (which is still not fixed)?
>
> I think the bigger issue is it needs to be decided what is proper behavior
> and document that. I'm not smart enough to know if this can be fixed
> properly without crippling these tools.

Newer sudo actually have a use_pty option that fixes the problem. 
It's not enabled by default though.
As I just found out there's also code missing to make sudo actually 
honor the option in the config (patch attached, CC'd upstream).
Introducing similar code in su would be possible but requires some 
programming effort. sudo has a liberal licence though so the code 
could probably be reused.

cu
Ludwig

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