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Message-ID: <CAJ_zFkKL6O2mH3WBjCG5JR=2N3aw6idiLT4_PZC9TOD76MpPFA@mail.gmail.com>
Date: Wed, 15 Apr 2015 09:45:07 -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 9:36 AM, Tyler Hicks <tyhicks@...onical.com> wrote:
> On 2015-04-15 09:21:39, Tavis Ormandy wrote:
>> 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.
>
> Ah, right. Looking at the real uid in /proc/ppid/status is the way to do
> it.
>
>>
>> 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.
>
> That's why I suggested that he chdir('/proc/ppid') and then only work
> off of relative paths. I assumed that would be sufficient but I'll
> verify that.
That's true, but there's a race between reading the Ppid and the chdir.
Tavis.
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