Re: [kernel-hardening] Re: [PATCH 2/2] sysctl: allow CLONE_NEWUSER to be disabled

[Andy Lutomirski]

On Sun, Jan 24, 2016 at 12:59 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Fri, Jan 22, 2016 at 4:59 PM, Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote:
>> On Fri, 2016-01-22 at 15:00 -0800, Kees Cook wrote:
>>> On Fri, Jan 22, 2016 at 2:55 PM, Robert ÅwiÄcki <robert@xxxxxxxxxxx> wrote:
>>> > 2016-01-22 23:50 GMT+01:00 Kees Cook <keescook@xxxxxxxxxxxx>:
>>> >
>>> > > > Seems that Debian and some older Ubuntu versions are already using
>>> > > >
>>> > > > $ sysctl -a | grep usern
>>> > > > kernel.unprivileged_userns_clone = 0
>>> > > >
>>> > > > Shall we be consistent wit it?
>>> > >
>>> > > Oh! I didn't see that on systems I checked. On which version did you find that?
>>> >
>>> > $ uname -a
>>> > Linux bc1 4.3.0-0.bpo.1-amd64 #1 SMP Debian 4.3.3-5~bpo8+1
>>> > (2016-01-07) x86_64 GNU/Linux
>>> > $ cat /etc/debian_version
>>> > 8.2
>>>
>>> Ah-ha, Debian only, though it looks like this was just committed to
>>> the Ubuntu kernel tree too:
>>>
>>>
>>> > IIRC some older kernels delivered with Ubuntu Precise were also using
>>> > it (but maybe I'm mistaken)
>>>
>>> I don't see it there.
>>>
>>> I think my patch is more complete, but I'm happy to change the name if
>>> this sysctl has already started to enter the global consciousness. ;)
>>>
>>> Serge, Ben, what do you think?
>>
>> I agree that using the '_restrict' suffix for new restrictions makes
>> sense.  I also don't think that a third possible value for
>> kernel.unprivileged_userns_clone would would be understandable.
>>
>> I would probably make kernel.unprivileged_userns_clone a wrapper for
>> kernel.userns_restrict in Debian, then deprecate and eventually remove
>> it.
>
> Okay, cool. We'll keep my patch as-is then. Thanks!

We still need to deal with the capable check in the write handler though, right?

But I must be missing something: why is mode 0644 insufficient?

--Andy