[erlang-questions] low level packet access from erlang

Garry Hodgson garry@REDACTED
Thu Apr 4 19:58:59 CEST 2013

wow. this looks great. you've built up a nice set of layers here.
i was just tinkering with procket when i saw this message.
guess i need to keep on tinkering.


On 04/03/2013 05:24 PM, Michael Santos wrote:
> On Wed, Apr 03, 2013 at 01:59:47PM -0400, Garry Hodgson wrote:
>> i am building an experimental firewall of sorts,
>> and need to be able to access incoming packets
>> directly, so i can muck around with low level
>> src/dst/ports/etc information. it looks like the standard
>> modules handle the low level things for me, such that
>> i by the time i see an incoming message, the low level
>> details are lost.
>> how can i arrange access to the lower level information
>> (ignoring performance issues for now)?
>> i see like mentioned a way in an old (2001) thread:
>> http://www.trapexit.org/forum/viewtopic.php?p=4258&sid=4469db61020efe9100e1e1c2504bfc8c
>> but the link to bluetail where his code was doesn't exist anymore.
>> i've read the ei/pcap approach presented here:
>> http://blog.listincomprehension.com/2009/12/erlang-packet-sniffer-using-ei-and.html
>> but i don't want to just sniff packets, but intercept them.
>> i'd appreciate any insights into how to tackle this.
> It really depends on what level and which platforms you want to work
> on. There are BSD raw sockets, the Linux PF_PACKET interface, BPF for
> BSD and LSF for Linux, divert sockets, tun devices, tap devices ...
> procket can handle all of those but assuming you just want to manipulate
> the IP headers and don't want to worry about the ethernet framing,
> maybe using a tun device would be the easiest way.
> I wrote an Erlang tun/tap interface on top of procket:
> https://github.com/msantos/tunctl
> I've tested the code on Linux, Mac OS X and FreeBSD. Supporting other
> BSDs shouldn't be a problem. Adding Windows support is on my TODO list.
> Once you've created an interface and set up the routing table, you can
> simply read/write frames to the device.  Here is an example of using a tap
> device to create the most insecure VPN ever over Erlang distribution:
> https://github.com/msantos/tunctl/blob/master/examples/vpwn.erl
> Another example using a tun device:
> https://github.com/msantos/sut
> sut sets up an RFC 4213 IPv6 over IPv4 tunnel. There is an example of
> creating a basic stateless firewall here:
> https://github.com/msantos/sut/blob/master/examples/basic_firewall.erl

Garry Hodgson
AT&T Chief Security Office (CSO)

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