Re: [Qemu-devel] [PATCH] Slirp reverse UDP firewall

[Stefan Berger]

On 04/12/2011 12:19 PM, Daisuke Nojiri wrote:

This patch adds: -drop-udp, -allow-udp ADDR:PORT, -drop-log FILE

  e.g.) $ qemu -net user -drop-log qemu.drop -drop-udp -allow-udp 10.0.2.3:53

-drop-udp enables usermode firewall for out-going UDP packats from a guest.

All UDP packets except ones allowed by -allow-udp will be dropped. Dropped

packets are logged in the file specified by FILE. PORT can be a single number

(e.g. 53) or a range (e.g. [80-81]). If ADDR is ommitted, all addresses match

the rule.

If you want to end up providing functionality like ebtables/iptables does then you'll need to think of user-defined tables or 'labeled rules' along with gotos/jumps -- not just for efficiency reasons but also because strictly linear evaluation of rules doesn't cover all the cases.
Besides that you'd probably want a connection tracking system so that you can for example enable only a few [UDP] ports of the VM to be reachable yet can initiate any kind of traffic... A bigger undertaking to say the least.

My $.02,
   Stefan