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

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

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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 <http://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


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