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>, Stéphane 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 Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)
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