Re: udevadm etc

[Chris PeBenito <pebenito@ieee.org>]

On 12/9/20 7:02 PM, Russell Coker wrote:
> On Thursday, 10 December 2020 9:00:38 AM AEDT Chris PeBenito wrote:
>> On 12/9/20 7:38 AM, Russell Coker wrote:
>>> In systemd verision 247.1 (which is in Debian/Unstable now) systemd-udevd
>>> is a symlink to udevadm.  In systemd version 241 (in Debian/Buster) it's
>>> not a symlink.  The systemd changelog doesn't mention this change so I
>>> don't know exactly when it happened.
>>>
>>> type_transition init_t udevadm_exec_t:process udevadm_t;
>>> type_transition initrc_t udevadm_exec_t:process udevadm_t;
>>> type_transition sysadm_t udevadm_exec_t:process udevadm_t;
>>> type_transition consolekit_t udev_exec_t:process udev_t;
>>> type_transition devicekit_disk_t udev_exec_t:process udev_t;
>>> type_transition hald_t udev_exec_t:process udev_t;
>>> type_transition hotplug_t udev_exec_t:process udev_t;
>>> type_transition init_t udev_exec_t:process udev_t;
>>> type_transition initrc_t udev_exec_t:process udev_t;
>>> type_transition kernel_t udev_exec_t:process udev_t;
>>> type_transition virtd_t udev_exec_t:process udev_t;
>>>
>>> Above is a list of the relevant type_transition rules from refpolicy taken
>>> from git 3 days ago (there don't appear to be any udev changes since
>>> then).
>>>
>>> I think that the only thing to do is to have init_t and initrc_t run
>>> udevadm in the udev_t domain.
>>>
>>> Is it worth having a udevadm_t domain just for running it from sysadm_t or
>>> should we have that run as udev_t too?
>>
>> The udevadm_t domain is much smaller than udev_t, and critically doesn't
>> have all the device access udev_t has.  Systemd merging the binaries into
>> one doesn't necessarily mean the policy has to merge too.
> 
> Currently only 3 domains can transition to udevadm_t.  2 of those 3 also
> transition to udev_t so they can't use udevadm_t without code changes.  The
> only remaining domain is sysadm_t.
> 
> The question is not "do we have to merge the policy because systemd merges
> binaries" but "should we have a separate domain only used for sysadm_t"?

Ah, I misunderstood.  The alternate question is, should any of these domains 
that transition to udev_t actually transition to udevadm_t instead? For a long 
time udevadm was labeled udev_exec_t.

I did some cursory searching in devicekit and I see udisks execs udevadm.  I 
couldn't find any instance of it executing udev, so there is a possibility of 
udevadm_t being more useful.

If it ends up with sysadm_t being the only one that only execs udevadm, then I 
agree that udevadm_t doesn't provide the hoped benefits.

-- 
Chris PeBenito