[asterisk-users] TOS and security

Dave Platt dplatt at radagast.org
Fri Jul 18 22:35:47 CDT 2008


> I'm preparing for a client install of * by doing a fresh one in-house.  
> Unlike my earlier installation that runs asterisk as superuser, my 
> current experimental box runs without such privilege.  This is causing 
> it to moan that it can't set TOS.  I absolutely don't want to install it 
> on the client LAN without this capability.  If need be, I'll set the 
> binary to run setuid root.
>
> But I'm looking for something more elegant.  While googling, I found a 
> suggestion to use iptables mangle rules to set TOS for all packets going 
> out of the box on ports like 5060 and 10000:20000.  Not a bad hack, but 
> indiscriminate and this box will be handling other traffic besides the 
> RTP.  I'd like to do better.

It is possible for an iptables filter/rule to match packets in the
OUTPUT chain based on the UID or GID of the process which created
them, if you have the "owner" module loaded.  You should be able to
add a rule to the OUTPUT chain of the mangle table which will set the
TOS properly for any and all outbound packets generated locally by the
non-root user ID which you're using to run Asterisk.

Come to think of it, I think I need to do this myself.  I'm using the
"ultimate Linux traffic conditioning" configuration (modified very
slightly) to prioritize my system's outbound traffic into multiple
queues by TOS, and it's probably mis-queueing the RTP traffic because
my Debian install of Asterisk is running under a non-root UID.

> I thought of using POSIX access control to enable asterisk to do TOS 
> setting without being root (would this be CAP_NET_RAW?), which sounds 
> perfect, but so far I'm operating with stock ubuntu hardy, and I would 
> like to avoid a kernel build to add this capability.
>
> Any other ideas?

Seems like "iptables -t mangle -A OUTPUT -m owner --uid-owner $ASTERISK"
would be along the lines of what you want?  Mark the packets with the
TOS you want... and then consider using the Linux traffic-shaping
system to make sure that they really do get transmitted ahead of
non-urgent packets:

  http://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.cookbook.ultimate-tc.html



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