[LEDE-DEV] running stuff as !root

[David Lang]

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
> 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.

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.

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)

David Lang