Re: Re: [LightDM] Version 1.0.6 released

[Guido Berhoerster <gber () opensuse org>]

* Robert Ancell <robert.ancell () canonical com> [2011-11-11 07:21]:
> On 10/11/11 23:57, Guido Berhoerster wrote:
> > * Marc Deslauriers <marc.deslauriers () canonical com> [2011-11-09 16:47]:
> > > On Wed, 2011-11-02 at 10:40 -0600, Kurt Seifried wrote:
> > > > On 11/02/2011 10:31 AM, Yves-Alexis Perez wrote:
> > > > > On mer., 2011-11-02 at 10:16 -0600, Kurt Seifried wrote:
> > > > > > On 11/02/2011 09:54 AM, Yves-Alexis Perez wrote:
> > > > > > > On mer., 2011-11-02 at 11:42 -0400, Robert Ancell wrote:
> > > > > > > > Fixes a security issue where using ~/.Xauthority as a symlink would
> > > > > > > > cause LightDM to set the destination of the link to user ownership.
> > > > > > > > All users of 1.0.4 or 1.0.5 should upgrade immediately.
> > > > > > > >
> > > > > > > > Overview of changes in lightdm 1.0.6
> > > > > > > >
> > > > > > > >     * Use lchown for correcting ownership of ~/.Xauthority instead of chown
> > > > > > > Could a CVE be assigned for this?
> > > > > > >
> > > > > > > Regards,
> > > > > > Can you send me the link to this announcement so I can confirm it? Thanks.
> > > > > Here's the link to the mailing list mail:
> > > > > http://lists.freedesktop.org/archives/lightdm/2011-November/000178.html 
> > > > >
> > > > > Regards,
> > > > Thanks, confirmed (first hand info is much better). Please use
> > > > CVE-2011-4105 for this issue.
> > > BTW, the fix that is in 1.0.6 is probably not enough for distros that
> > > don't implement hard link restrictions, such as the Yama LSM that is
> > > used in Ubuntu.
> > Does an incomplete fix in a released version warrant a new CVE?
> >
> > I've attached a suggested fix.
> Note the attached patch can still be exploited; if the file changes from
> a standard file to a hard link / symlink between the lstat and the
> fchown then lightdm can be fooled into thinking it's safe when it's

Replacing the file between the lstat and the open would change
its inode and then be caught by the check before the fchown, no?

-- 
Guido Berhoerster