[Pianod] Problem with RasPi sound card access as user nobody

[Peter Li]

Seems like we could have in addition to drop_root_privs a function that 
adds audio to the setgroups if it's not in getgroups or getgid already?  
I believe this patch would make sense across Linux systems, but I think 
it doesn't make sense for Mac.  Should work to just check whether 
getgrnam returns anything for "audio" though?


On 05/30/2013 11:05 PM, Peter Li wrote:
> If I hack settings.c, drop_root_privs to set gid to the audio gid 
> instead of the nobody user gid (nogroup) it also works.
>
> So even though nobody is now set to be a member of the audio group, 
> and pianod is getting setuid to nobody, it needs to have setgid audio 
> instead of setgid nogroup to work.
>
> Now I notice that if I add root to the audio group and hack settings.c 
> back to dropping to gid nogroup it also seems to work.  So apparently 
> after pianod drops to nobody, it has:
>     1) uid of nobody
>     2) gid of nogroup
>     3) additional groups of /root/ not groups of /nobody/
>
> So I guess this is the expected behavior and I just didn't understand 
> it.  Should the fix just be to put root in the audio group?  Or should 
> we try to change drop_root_privs so that it will take on the 
> additional groups of nobody?

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