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Date: Thu, 16 Apr 2015 13:17:07 -0500
From: Tyler Hicks <tyhicks@...onical.com>
To: Tavis Ormandy <taviso@...gle.com>
Cc: oss-security@...ts.openwall.com,
	Assign a CVE Identifier <cve-assign@...re.org>,
	security <security@...ntu.com>,
	St├ęphane Graber <stgraber@...ntu.com>
Subject: Re: Re: Problems in automatic crash analysis
 frameworks

On 2015-04-15 20:05:30, Tavis Ormandy wrote:
> On Wed, Apr 15, 2015 at 12:55 PM, Tavis Ormandy <taviso@...gle.com> wrote:
> > On Wed, Apr 15, 2015 at 11:48 AM, Tavis Ormandy <taviso@...gle.com> wrote:
> >> FWIW, I verified this is exploitable.
> >>
> >
> > Here's the script I used to verify, it should create the file
> > /etc/rootfiletest. By using the partial trick or creating parse
> > errors, this is easy to turn into a root shell.
> 
> It looks like there's a new patch here:
> https://launchpadlibrarian.net/203416094/apport.diff
> 
> In get_parentns_pid code, it looks like it has the same problem as
> before in that there's no guarantee ppid isn't recycled (possibly by
> root). Also, you can easily get an untrusted process reparented to
> init. If you're not convinced of this, try this:
> 
> $ bash -c 'sleep 600 & echo $!; disown -ah'
> 28396
> $ egrep '(PPid|Name):' /proc/28396/status
> Name: sleep
> PPid: 1
> 
> I'm almost certain it's not possible for the core_patten handler to
> perform any meaningful analysis on the parent process.
> 
> This code is definitely not sufficient:
> 
>         os.chdir("/proc/%s/" % ppid)
>         ...
>         with open("status", "r") as fd:
>         ....
>                             if line.startswith("Uid:"):
> 
> 
> Because you can just wait for ppid to be recycled before the chdir().
> The UDS inode validation is a neat idea, but I don't think it works -
> the obvious case is reparenting to init and then using one of the
> inode numbers init uses, but even if you special-case init, pid
> recycling is possible.
> 
> I saw the duplicate inode checks, but that doesn't work....it's racy,
> and you can just use a netlink socket or similar.
> 
> Once you've passed this check, it's a controlled lxc.Container() and
> you can use my previous PoC to verify that is exploitable.

We've decided to disable support for gathering crash reports of
containerized processes (see USN-2569-2).

We may reintroduce the feature, with a different implementation, in the
future. The current idea is described in this feature bug:

  https://launchpad.net/bugs/1445064

Please leave any comments on the proposed design in the feature bug.

Many thanks for thinking through the old implementation and follow up
patches, Tavis.

Tyler

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