poll() call gives POLLERR, then hangs

poll() call gives POLLERR, then hangs

[Ingmar Schuster]

Hi all,

in a userspace firewall (using libnetfilter_queue-0.0.17,  
libnfnetlink-0.0.41) I'm writing some strange behavior appeared when  
testing with tcpreplay.
Starting tcpreplay on another computer to replay packets onto the  
firewall, the packets are received in userspace at first. After a  
while the poll() call sets POLLERR in revents, and after a while calls  
to poll() just wont return to the calling function. More exactly, it  
is  __kernel_vsyscall() that doesn't return. Starting netcat in  
parallel to tcpreplay makes poll() on the firewall return.

Does anybody have an idea what's causing this?

Thanks
Ingmar

Re: poll() call gives POLLERR, then hangs

[Ingmar Schuster]

Hey,

solved the problem already. It turned out not to be a bug in netfilter.
First there was a slight error in the way I rewrote the MAC addresses in 
the pcap file. Then tcprewrite had a bug that caused one MAC to be 
rewritten incorrectly. I fixed that with a sed-like tool called bbe.

Yours
Ingmar


Pablo Neira Ayuso schrieb:
> if you can send a very small pet program that can allow me to reproduce
> this error that you're reporting, it would be much easier to diagnose.
>