WARNING in apparmor_secid_to_secctx

From: dvyukov@google.com (Dmitry Vyukov)
To: linux-security-module@vger.kernel.org
Subject: WARNING in apparmor_secid_to_secctx
Date: Fri, 31 Aug 2018 15:38:12 -0700	[thread overview]
Message-ID: <CACT4Y+YOxTTYzEi3uCeLm3gquvSkJNZ+DhPVziEnbXGX6HVkVA@mail.gmail.com> (raw)
In-Reply-To: <4b37e892-4d79-aefb-92ab-7753b89b8963@tycho.nsa.gov>

On Fri, Aug 31, 2018 at 9:17 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 08/31/2018 12:16 PM, Stephen Smalley wrote:
>>
>> On 08/31/2018 12:07 PM, Paul Moore wrote:
>>>
>>> On Fri, Aug 31, 2018 at 12:01 PM Stephen Smalley <sds@tycho.nsa.gov>
>>> wrote:
>>>>
>>>> On 08/29/2018 10:21 PM, Dmitry Vyukov wrote:
>>>>>
>>>>> On Wed, Aug 29, 2018 at 7:17 PM, syzbot
>>>>> <syzbot+21016130b0580a9de3b5@syzkaller.appspotmail.com> wrote:
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> syzbot found the following crash on:
>>>>>>
>>>>>> HEAD commit:    817e60a7a2bb Merge branch 'nfp-add-NFP5000-support'
>>>>>> git tree:       net-next
>>>>>> console output:
>>>>>> https://syzkaller.appspot.com/x/log.txt?x=1536d296400000
>>>>>> kernel config:
>>>>>> https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
>>>>>> dashboard link:
>>>>>> https://syzkaller.appspot.com/bug?extid=21016130b0580a9de3b5
>>>>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>>>>
>>>>>> Unfortunately, I don't have any reproducer for this crash yet.
>>>>>>
>>>>>> IMPORTANT: if you fix the bug, please add the following tag to the
>>>>>> commit:
>>>>>> Reported-by: syzbot+21016130b0580a9de3b5 at syzkaller.appspotmail.com
>>>>>
>>>>>
>>>>> Hi John, Tyler,
>>>>>
>>>>> I've switched syzbot from selinux to apparmor as we discussed on lss:
>>>>>
>>>>> https://github.com/google/syzkaller/commit/2c6cb254ae6c06f61e3aba21bb89ffb05b5db946
>>>>
>>>>
>>>> Sorry, does this mean that you are no longer testing selinux via syzbot?
>>>>    That seems unfortunate.  SELinux is default-enabled and used in
>>>> Fedora, RHEL and all derivatives (e.g. CentOS), and mandatory in Android
>>>> (and seemingly getting some use in ChromeOS now as well, at least for
>>>> the Android container and possibly wider), so it seems unwise to drop it
>>>> from your testing altogether.  I was under the impression that you were
>>>> just going to add apparmor to your testing matrix, not drop selinux
>>>> altogether.
>>>
>>>
>>> It is also important to note that testing with SELinux enabled but no
>>> policy loaded is not going to be very helpful (last we talked that is
>>> what syzbot is/was doing).  While syzbot did uncover some issues
>>> relating to the enabled-no-policy case, those are much less
>>> interesting and less relevant than the loaded-policy case.
>>
>>
>> I had thought that they had switched over to at least loading a policy but
>> possibly left it in permissive mode because the base distribution didn't
>> properly support SELinux out of the box.  But I may be mistaken.
>> Regardless, the right solution is to migrate to testing with a policy
>> loaded not to stop testing altogether.
>>
>> Optimally, they'd test on at least one distribution/OS where SELinux is in
>> fact supported out of the box, e.g. CentOS, Android, and/or ChromeOS.
>
>
> Or Fedora, of course.

Hi,

Yes, we switched from selinux to apparmor. The thing is that we
effectively did not test selinux lately, so it's more like just
enabling apparmor rather than disabling selinux.

The story goes as follows.
We enabled selinux, but did not have policy and selinux wasn't enabled.
Then Paul (I think) pointer that out. After some debugging I figured
out that our debian wheezy actually has a policy, it's just that
selinux utilities were not installed, so init could not load the
policy.
I installed the tools, and we started loading policy.
But then it turned out that wheezy policy does not allows mounting
cgroup2 fs and maybe some others even in non-enforcing mode. As far as
I understand that's because the policy does not have definition for
the fs, and so loading bails out with an error.
We need cgroup2 both for testing and for better sandboxing (no other
way to restrict e.g. memory consumption). Moreover, we did not test
any actual interesting interactions with selinux (there must be some?
but I don't know what are they).
So I had to uninstall the tool and policy is not loaded again.
I investigated building a newer debian image with debootstrap (which
should have newer policy I guess). But they don't work, some cryptic
errors in init. Other people reported the same.
So that's we are. I don't have any ideas left...