Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction

[Djalal Harouni]

On Mon, Apr 24, 2017 at 8:02 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Mon, Apr 24, 2017 at 7:25 AM, Djalal Harouni <tixxdz@xxxxxxxxx> wrote:
>> On Sat, Apr 22, 2017 at 9:29 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> On Fri, Apr 21, 2017 at 11:51 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>>>> On Fri, Apr 21, 2017 at 5:12 PM, Djalal Harouni <tixxdz@xxxxxxxxx> wrote:
>>>>> On Sat, Apr 22, 2017 at 1:51 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>>>>>
>> [...]
>>>>> * DCCP use after free CVE-2017-6074
>>>>> * n_hldc CVE-2017-2636
>>>>> * XFRM framework CVE-2017-7184
>>>>> * L2TPv3 CVE-2016-10200
>>>>>
>>>>> Most of these need CAP_NET_ADMIN to be autoloaded, however we also
>>>>> need CAP_NET_ADMIN for other things... therefore it is better to have
>>>>> an extra facility that could coexist with CAP_NET_ADMIN and other
>>>>> sandbox features.
>>>>>
>>>>
>>>> I agree that the feature is important, but I think your implementation
>>>> is needlessly dangerous.  I imagine that the main uses that you care
>>>> about involve containers.  How about doing it in a safer way that
>>>> works for containers?  I can think of a few.  For example:
>>>>
>>>> 1. A sysctl that, if set, prevents autoloading outside the root
>>>> userns.  This isn't very flexible at all, but it might work.
>>>>
>>>> 2. Your patch, but require privilege within the calling namespace to
>>>> set the prctl.
>>>
>>> How about CAP_SYS_ADMIN || no_new_privs?
>>>
>>> -Kees
>>>
>>
>> Yes I can update as per Andy suggestion to require privileges inside
>> the calling namespace to set prctl. Other options that are not prctl
>> based have more variants, that make them hard to use.
>>
>> So I would got with CAP_SYS_ADMIN in the calling userns ||
>> no_new_privs , I would have said CAP_SYS_MODULE in the userns but it
>> seems better to standardize on CAP_SYS_ADMIN to set the prctl.
>
> Andy's concern is that it would provide an escalation from SYS_MODULE
> to SYS_ADMIN through some privileged process being tricked through a
> missing API provided by modules, so we have to use either SYS_ADMIN ||
> nnp.

Yes, I would say that programs expect that maybe such functionality is
not provided, but we don't know. I will update.

Thanks!


-- 
tixxdz