[LEDE-DEV] running stuff as !root

[Ferry Huberts]

On 18/05/16 10:03, David Lang wrote:
> On Wed, 18 May 2016, John Crispin wrote:
>
>> On 18/05/2016 09:46, Ferry Huberts wrote:
>>>
>>>
>>> On 18/05/16 09:25, John Crispin wrote:
>>>>
>>>>
>>>> On 18/05/2016 09:21, Radu Anghel wrote:
>>>>> /* sending again because i hit 'reply' instead of 'reply all' :) */
>>>>>
>>>>> On Wed, May 18, 2016 at 8:29 AM, John Crispin <john at phrozen.org>
>>>>> wrote:
>>>>>>
>>>>>> ok, there had been some discussion about building a super daemon that
>>>>>> runs, then ld-preloading bind() and co and using ubus to transport
>>>>>> sockets around. using caps or /proc sounds like a good i between
>>>>>> until
>>>>>> such a daemon exists
>>>>>>
>>>>>
>>>>> Most daemons I know of that need to bind to ports <1024 start as root
>>>>> and after binding to the port they drop privileges to the privileges
>>>>> of the user specified in their config file. For those daemons just
>>>>> adding a user and specifying it in their config file should be enough.
>>>>> For the daemons that don't need to bind to <1024 just starting them
>>>>> from their own user account is ok as they don't need additional
>>>>> privileges.
>>>>>
>>>>> For example the dnsmasq daemon has these options:
>>>>>
>>>>> # If you want dnsmasq to change uid and gid to something other
>>>>> # than the default, edit the following lines.
>>>>> #user=
>>>>> #group=
>>>>>
>>>>> I don't think that integrating such functionality in ubus or some
>>>>> other LEDE-only super-daemon is a good idea. Config options +
>>>>> capabilities for those daemons withut such options is a good way of
>>>>> doing this in my opinion. Also use different users for different
>>>>> daemons, as others said.
>>>>
>>>> to elaborate, imagine dnsmasq running inside a jailm where ut only
>>>> thinks it is root but is not in reality. also ld-preloading bind and
>>>> connect would allow us to do pretty adavnced stuff like only allowing
>>>> dnsmasq to open certain ports. essentially an acl around the
>>>> bind/connect calls.
>>>>
>>>
>>>
>>> You might just as well switch on SELinux and use the policies that are
>>> already in-place in Fedora and RedHat/CentOS.
>>>
>>> You then get even stronger protection and run-time performance impact is
>>> negligible.
>>>
>> the stuff i proposed has not runtime hit. selinux is simple to full

SELinux's hit is for all intents and purposes zero as well nowadays.

>> blown and hard to maintain. the idea would be to create a custom
>> tailored solution for our requirements.
>
> That is why I prefer AppArmor, you don't have the interaction between
> different application configs that you do with SELinux, so you can focus
> on the specific application that you are concerned about.

AppArmor is significantly less secure than SELinux.
And with SELinux you don't need all the preloading stuff that was talked 
about, you can just declare which ports are allowed.

>
> SELinux configs that Fedora uses have to be so permissive to keep from
> breaking too many 'normal' use cases that I really question how valuable
> they are.

And this is based on what exactly?
I've been using Fedora ever since SELinux was first enabled and I don't 
see that. Processes are well secured.
If you think about stuff like Firefox, then ok, that one is really hard 
to secure, better run it in a sandbox.
But process that are well-defined in behaviour are well secured.



>
> A SELinux system tuned by an expert is going to be more secure than an
> AppArmor system tuned by an expert, SELinux just can do more (at least
> right now). But there aren't many experts of that caliber around. A
> reasonably competent sysadmin can understand an AppArmor config and
> tweak it for their layout without too much effort (once they identify
> that AppArmor is blocking what they are trying to do)
>


Agreed, it is a balance.

However, I must note that I've encountered very few cases where the 
policy had to be tweaked, on my laptops, desktop and most of all servers.

One example of tweaking is when I move a service to a different port.
That is a single command, like (moving the port of the 'cockpit' service):
> semanage port -a -t websm_port_t -p tcp "$newport"



My 2 cents :-)





> David Lang
>
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-- 
Ferry Huberts