[LEDE-DEV] convention on uid/gid for packages

[Yousong Zhou]

On 15 May 2017 at 21:07, Val Kulkov <val.kulkov at gmail.com> wrote:
> On 15 May 2017 at 02:30, Alexandru Ardelean <ardeleanalex at gmail.com> wrote:
>> On Sun, May 14, 2017 at 3:59 AM, Daniel Golle <daniel at makrotopia.org> wrote:
>>> Hi Val,
>>>
>>> On Sat, May 13, 2017 at 06:23:29PM -0400, Val Kulkov wrote:
>>>> Is there any convention on the use of uid and gid when creating new
>>>> users or groups? Can someone point me to it, if it exists?
>>>>
>>>> I noticed that two packages, icecast and postfix, compete for the same uid=87:
>>>>
>>>> icecast's Makefile:
>>>>   USERID:=icecast=87:icecast=87
>>>>
>>>> postfix's postfix.init:
>>>>   user_exists postfix || user_add postfix 87
>>>
>>> This looks wrong to me (user_add in the init script)...
>>>
>>>>
>>>> There may be more packages competing for the same uid/gid's, I have
>>>> not fully researched it.
>>>>
>>>> I am preparing a new package, opendkim, which should be run as a
>>>> non-privileged user. For this,
>>>> USERID:=opendkim=<something>:opendkim=<something> seems appropriate,
>>>> but what numbers should I assign?
>>>
>>> I run into this issue before and believe that we should have a wiki
>>> page which allows registering static UIDs/GIDs at least for the
>>> packages which actually need that (ie. if a specific UID or GID is
>>> referenced in other packages, or scripts like firewall rules, ...).
>>> Grep'ing for USERID allows to automatically generate that list based
>>> on the currently available packages very easily.
>>>
>>> Examples from elsewhere for inspiration:
>>>
>>> FreeBSD got those lists
>>> https://svnweb.freebsd.org/ports/head/UIDs?view=markup
>>> https://svnweb.freebsd.org/ports/head/GIDs?view=markup
>>>
>>> linuxfromscratch got a much smaller list for essential/system UIDs/GIDs
>>> http://linuxfromscratch.org/blfs/view/svn/postlfs/users.html
>>>
>>>
>>> Cheers
>>>
>>
>> Just woke up from the weekend.
>> I recommend trying this out [based on lldpd] :
>> https://github.com/lede-project/source/blob/master/package/network/services/lldpd/Makefile#L35
>> We use lldpd and this seems to work ; lldpd does some priv separation.
>>
>> Alex
>
> Alexandru, the USERID:= construct works really well, but my question
> was about the convention to avoid conflicts while picking numbers for
> new UID and GID. For example, icecast and postfix both use 87 for a
> new UID they create.
>
> I think the links to FreeBSD's UID and GID lists that Daniel provided
> are indeed an excellent source of inspiration. We should a Wiki page
> with a similar content.
>

If it's only about allocation of uid/gid without collision, then the
default_postinst() func will just do that [1], e.g.
USERID:=icecast:icecast

I do not know of any service checking non-root username of its
effective uid/gid and quit if they fail expectation.  The other thing
is that if we allow auto-allocation with default_postinst and preserve
/etc/{passwd,group} across sysupgrade, then the global allocation of
uid/gid may not work out because those slots may already be taken up
by the auto-allocation happen prior of time...

 [1] https://github.com/openwrt/packages/pull/3150#discussion_r83354888