[LEDE-DEV] umdns fails to launch (seccom related)?

[Bryan Mayland]

I use a custom LEDE build as the basis for an open source project and
noticed recently that the umdns daemon has stopped loading. This also
occurs with the standard development snapshot with the umdns package
installed.
root at LEDE:~# /etc/init.d/umdns restart
Command failed: Request timed out

umdns never launches so the service_started() handler waits for the 10
seconds for the ubus response then fails. If I comment out the
`procd_set_param seccomp /etc/seccomp/umdns.json` line it works just
fine. I've also tried replacing the umdns executable with a simple
shell script and it never appears to execute. This occurs if the
daemon is configured to be jailed or not.

Because my bcm2708 target does not have CONFIG_KERNEL_SECCOMP enabled,
this should not make a difference right? I've also tried adding a
/sbin/seccomp-trace which was just a shell script as well to launch
umdns and it had no effect.

I believe it is a problem in procd but I'm not sure where else to look
as this seems like it could affect anything with a seccomp procd init,
and umdns is the only one that does this so far.