Re: A bug in IPQ or just my misunderstanding ?

[Toby Bradshaw <toby.bradshaw@rawflow.com>]

Patrick McHardy wrote:
> Toby Bradshaw wrote:
>   
>> Hi,
>>
>> I've been trying to get userspace packet mangling to work with a simple
>> example app. the main details of which are (cribbed from the usual
>> example on the man pages):
>>
>> case IPQM_PACKET:
>> {
>>    ipq_packet_msg_t *m = ipq_get_packet(buf);
>>    status = ipq_set_verdict(h, m->packet_id, NF_ACCEPT, m->data_len,
>> m->payload);
>>
>>    if (status < 0)
>>      die(h);
>>    break;
>> }
>>
>> So i'm just basically just resubmitting the unchanged payload. This
>> doesn't seem to work. If I copy the packet into new memory and submit it
>> also doesn't work. A sanity-checking memcmp shows the two buffers to be
>> identical.
>>
>> I'm testing this by pinging a subinterface on my host (ifconfig eth0:1
>> 192.168.8.150 up; ping 192.168.8.150). The iptables QUEUE is working
>> fine, packets are delivered to my app.
>>
>> If I don't submit a payload then as long as my app is running I'll get
>> ping replies. If I swap to a version that does submit the payload, the
>> replies stop. tcpdump proves that they're not being sent.
>>
>> In the payload submitting case I also notice the following via dmesg:
>>
>>    NF_IP_ASSERT: net/ipv4/netfilter/ip_nat_standalone.c:74(ip_nat_fn)
>>
>> .. which appear to be an assert concerning fragmentation.
>>
>> So.. am I not doing something right or is it possible this is a bug in
>> ipq_set_verdict or perhaps in ip_nat_standalone.c ??
>>     
>
> Looks like a bug. Which kernel version are you using, at what hook
> are you queueing packets?
>
>
>   
Sorry for any earlier copies of this message.. late night hacking..

Thanks for the reply.. apologies for the tardy reply but I got moved on 
to other things for while.

I've confirmed this problem with:

Mandriva Kernel 2.6.12
iptables v.1.3.3

I'm hooking at -t mangle -A PREROUTING which I inderstand to be the 
first point at which I could intercept a packet.

Can anyone post a known working userspace filter for me to compare 
against. Something that actually changes the packet. I'd really like to 
get this working as it would be immensely useful for us to simulate a 
variety of interesting firewall set-ups programmatically.

Thanks,

--
Toby