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Message-ID: <CAJ_zFkJ77jRVKqeM7oA52Etvp67AFvLPc+CUnBH2J6g+rs0NOg@mail.gmail.com>
Date: Wed, 15 Apr 2015 09:21:39 -0700
From: Tavis Ormandy <taviso@...gle.com>
To: Tyler Hicks <tyhicks@...onical.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 Wed, Apr 15, 2015 at 9:05 AM, Tyler Hicks <tyhicks@...onical.com> wrote:
> On 2015-04-14 17:16:08, Tyler Hicks wrote:
>> On 2015-04-14 14:10:12, Tavis Ormandy wrote:
>> > On Tue, Apr 14, 2015 at 2:08 PM, Tavis Ormandy <taviso@...gle.com> wrote:
>> > > On Tue, Apr 14, 2015 at 1:35 PM, Tavis Ormandy <taviso@...gle.com> wrote:
>> > >> On Tue, Apr 14, 2015 at 9:02 AM, Marc Deslauriers
>> > >> <marc.deslauriers@...onical.com> wrote:
>> > >>> Hi,
>> > >>>
>> > >>> On 2015-04-14 11:55 AM, cve-assign@...re.org wrote:
>> > >>>> This is mostly a question for the persons who assigned CVE-2015-1318
>> > >>>> and CVE-2015-1862. Should these CVE assignments be interpreted to
>> > >>>> mean:
>> > >>>>
>> > >>>> CVE-2015-1318 - in Apport, an unprivileged user can use a
>> > >>>> namespace-based attack because there is an execve by
>> > >>>> root after a chroot into a user-specified directory
>> > >>>
>> > >>> Yes, I assigned CVE-2015-1318 to that specific issue in Apport.
>> > >>>
>> > >>> Marc.
>> > >>
>> > >> It looks like this is the patch for Apport:
>> > >>
>> > >> http://bazaar.launchpad.net/~apport-hackers/apport/trunk/revision/2943#data/apport
>> > >>
>> > >> It's far more complicated than I expected, and not obviously correct.
>> > >> It could probably use some review, I'll think about it today.
>> > >>
>> > >> Tavis.
>> > >
>> > > Wait, my first thought is that it's not obvious to me that
>> > > /proc/net/unix is guaranteed to be newline delimited, newline is a
>> > > perfectly valid name in a filename, no?
>> > >
>> > >>>> import socket
>> > >>>> socket.socket(socket.AF_UNIX, socket.SOCK_STREAM).bind('test\ntest')
>> > >>>> sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
>> > >>>> sock.bind('/tmp/foo\nbar')
>> > >>>> sock.listen(1)
>> > >
>> > > $ grep -A1 foo /proc/net/unix
>> > > 0000000000000000: 00000002 00000000 00010000 0001 01 4772228 /tmp/foo
>> > > bar
>> >
>> > And with complete control over this line, it seems like it's game over.
>> >
>> > container = lxc.Container(path[-2], real_path)
>> >
>> > I'm calling this re-broken.
>>
>> I've pointed Stéphane Graber to your analysis (and put him on cc). He's
>> working on a fix.
>>
>> Even though it isn't clear if all of the checks added in revision 2943
>> can be bypassed, it is worth coming up with another approach.
>
> Hi Tavis - We've opened a bug to track the issue that you discovered:
>
> https://launchpad.net/bugs/1444518
>
> Stéphane has prepared a patch that is more resilient to a malicious
> /proc/net/unix:
>
> https://launchpadlibrarian.net/203372380/apport.diff
>
> Any feedback that you have would be appreciated. Thanks again!
>
> Tyler
Thanks Tyler, I'll think about this morning. I'm not sure if these
observations are important, but my first thought is It's definitely
possible to make the st_uid of /proc/ppid 0, you could just do su
$USER for example.
Also, you can at least trust /proc/pid is stopped while the core
handler is running, but ppid is still running. I think this matters,
because the pid might be recycled.
Tavis.
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