Re: Updated IP Blacklisting patch (version 2)

[Eoin Miller <eoin.miller () trojanedbinaries com>]

Martin Roesch wrote:
> Hi Eoin,
>
> That's what I was thinking of doing too.  Really I think it's a one
> liner change to do that, you just have to edit line 376 in
> src/preprocessors/spp_iplist.c from:
>
> SnortEventqAdd(GENERATOR_SPP_IPLIST, IPLIST_BLACKLIST, 1, 0, 0,
>
> to
>
> SnortEventqAdd(GENERATOR_SPP_IPLIST, (int)pn->data, 1, 0, 0,
>
> and that ought to do it.  Give it a shot and let me know if it works for you.
>
>
> Marty
>
>   

Marty,

After the update to the code, there was an 15% or so up-tick in system
processor utilization which is leading to exceptionally mild increase in
packet loss. Not really a surprise since when SnortEventqAdd is called,
it now does two lookups to find the number of the list and then the
number of the list again to refrence the name:

SnortEventqAdd(GENERATOR_SPP_IPLIST, (int)pn->data, 1, 0, 0,
list_names[(int)pn->data], 0);

So to try and streamline this a bit more, I added a new int inside of
IpListEval:

void IpListEval(Packet *p, void *conext)
{
int foo;


Then inside of the if(blacklist_detect) we grab (int)pn->data once and
then save it as foo and just use foo when calling SnortEventqAdd:

        if(blacklist_detect)
        {
            if(!noalerts)
                foo = (int)pn->data;
                SnortEventqAdd(GENERATOR_SPP_IPLIST, foo, 1, 0, 0,
                               list_names[foo], 0);


This drops the system processor utilization back down by about 10% or so
and completely stops the packet loss we were experiencing. Some links to
gnuplot graphs based off the snort.stats file are included below to
support this are below:

http://trojanedbinaries.com/security/snort/cpu.png
http://trojanedbinaries.com/security/snort/dropped.png


Hope this can prove useful!

--
Eoin Miller



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