"Really" enabling CGI in apache

This was driving me crazy. No matter what I did, apache just did not run CGI scripts. I did all the things people had said on various websites, like adding "AddHandler cgi-script .cgi" or adding "+ExecCGI" to options, but it did not work.

And finally, after hours of searching and trying, I got a hint from a very old apache documentation page that mentioned modules being enabled. I looked at my /etc/apache2, found two suspicious mods-available and mods-enabled sub-directories, confirmed that there was nothing called cgi in mods-enabled, symlinked anything with "cgi" in it from mods-available in mods-enabled, and at last, at long last, I got bugzilla working. Phew!

Using clang++ with waf

As far as I can see, the only way to make waf use clang C++ compiler is to run it like this:

$ CXX=clang++ ./waf configure

This makes waf use clang++ instead of g++ which seems to be the official way of doing this as it is mentioned in the documents here, except that the current documentation says to run it like this:

$ CXX=clang ./waf configure

which did not work for me. Apparently this causes the wrong standard library to be used.

Compiling PF_RING Intel Drivers

I've been meaning to play around with PF_RING but never really managed to get its patched drivers compiled. I'm running Arch Linux which has a 3.3 kernel at the moment. A while ago Luca Deri himself mentioned in a bug report of mine that the drivers are only meant to be compiled on 2.6.x kernels. So today I installed a Debian Squeeze which has a 2.6.32 kernel in VirtualBox and tried compiling the Intel drivers in there. Again I got an error but this time it was a different error message. Something like this:

error: ‘struct dev_pm_info’ has no member named ‘runtime_auto’

I found this thread that suggested making with make CFLAGS_EXTRA=-DDISABLE_PM. I tried the suggestion and it worked.

Unfortunately, the only PF_RING aware NIC I currently have access to is a Broadcom-based one. I haven't managed to compile those drivers yet.

Compiling "vomit"

I just needed to compile vomit (the man page is here) which is utility for converting G.711 data into a wave file. I ran into several problems (I'm using gcc 4.7.0, with libevent 2.0.18-1 from Arch's core repository, and libnet 1.1.5-2 from the community repo). In file pcapu.c, in function pcap_cb there is this line:

fprintf(stderr, __FUNCTION__": ! add\n");

There are several ways to fix this, but I shamelessly commented it out!

Then there are several references to struct libnet_ip_hdr, which does not exist in recent libnet versions. I simply changed them all to struct libnet_ipv4_hdr.

And finally, in vomit.c, there are references to event_gotsig and event_sigcb symbols which have been removed from libevent for some time. Again, since their use didn't seem too crucial to me, I commented them out.

Perhaps a little bit crude, but it worked for me!

libnids: I get nothing!

libnids is a library that emulates the IP stack of Linux 2.0.x. It offers IP defragmentation, TCP stream assembly and TCP port scan detection.

The first thing I attempted with it, naturally, was running the sample program, printatll.c. It's supposed to print out all TCP data. Problem was, it outputed nothing for me. I even added a printf to the first line of tcp_callback function and found out it is never called.

I was perplexed. I looked for a mailing list but found none. So I wrote to libnids's principal programmer, Rafal Wojtczuk, who kindly helped me with my problem. He suggested that probably I need to disable outgoing packet checksumming. I added these lines before the call to nids_run() and everything worked out!

struct nids_chksum_ctl *ctl =
  (struct nids_chksum_ctl *) malloc(sizeof(struct nids_chksum_ctl));
ctl->netaddr = 0;
ctl->mask = 0;
ctl->action = NIDS_DONT_CHKSUM;
nids_register_chksum_ctl(ctl, 1);

Apparently checksumming was somehow failing and stopping libnids to consider the TCP connection established (or something along those lines!). A big thanks to Rafal for his help.