December 10, 2012

Bro IDS on OpenWRT

Filed under: Blog — krkhan @ 12:59 pm

While I was at SysNet, we had been working on a project we called “Shrimp” — Software-defined Home Router Intelligent Monitoring Point. The goal of the project was to provide a framework for easy programmatic access to network monitoring on low-cost, commodity, home router devices. One of the requirements was to have an IDS on the home routers for which we chose Bro — the leading framework for semantic analysis of network traffic.

The OpenWRT OS was chosen as the target platform. Its SDK contained a cross-compile toolchain for CMake projects. However, during the compilation Bro tried to run the binpac and bifcl executables for processing intermediate files. The executables refused to run on the build platform if the target platform architecture was different (mostly the case, e.g., we were building on x86-64 and target was arm).

The (not-so-pretty ™) workaround we used was to build Bro twice. Once for the host, and once for the target. The CMake files were then patched to first generate binpac and bifcl binaries if they weren’t provided and then use the provided binaries if they were defined at make time. The first compile generated the binaries on x86-64 and the second compile (for arm) used the earlier binaries to process the bif files.

The Makefile and patches are available in this tarball: openwrt-bro.tar.gz, while the compiled ipk package is also available for installation. Here is a test execution of Bro on OpenWRT:

# bro –v
bro version 2.0
# cat test.bro
event bro_init()
	print "Hello World!";

event new_connection(c: connection)
	print "New connection created";
# bro test.bro
Hello World!
# bro -i br-lan test.bro
Hello World!
New connection created
New connection created
# ls
conn.log           notice_policy.log  reporter.log       weird.log
dns.log            packet_filter.log  test.bro

A heap of thanks to Zaafar for dealing with my messy code and providing the links to hosted files :) !

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