Inspirated

As I promised in the comments section of previous post, I set out on the adventure of recompiling Bro for Lantiq routers. As a result of the exercise I have new-found respect for open-source package maintainers. Holy waffles if troubleshooting build errors in a large Autotools mess isn’t the most hemorrhage-inducing activity known to mankind.

Anyways, this time I’ve tried to keep track of the changes I’ve been making along the way. The full set of updated Makefiles and patches is maintained in the openwrt-bro repo. Also, the compiled ipk packages for Atheros and Lantiq routers are available on the release page.

Now that I have a reasonably updated Buildroot on my system and an organized set of patches, feel free to request an ipk package for your router. While I can’t guarantee that the clusterfuck of patches will compile smoothly for your platform, I’ll still give it a try.

After posting the Bro port for OpenWRT on my blog roughly two years ago, I didn’t realize some people were already actually using it on their routers.

I had created an updated version of the port which I hadn’t posted on the blog. Digging in my archived files I finally found it today along with its sources:

• openwrt-bro-2.3.1.tar.gz
• bro_2.3.1-1_ar71xx.ipk

Word of caution though, my notes indicate that one of the default scripts was leaking memory and I never got around to figuring out which one. The workaround was to launch Bro in barebone mode with -b switch, which would prevent loading of default scripts.

# cat test.bro

event bro_init()
{
	print "Hello World!";
}

event new_connection(c: connection)
{
	print "New connection created";
}

# bro test.bro

Hello World!

# bro -C -b -i br-lan test.bro

Hello World!
New connection created
New connection created

If someone has cycles to spend and figure out which default script is leaking memory we can update the package to address the bug.

The paper chronicling our adventures with Bro IDS on home routers just got published in the latest issue of SIGCOMM CCR. Here’re the details:

Title: Rapid and Scalable ISP Service Delivery through a Programmable MiddleBox

Abstract: With only access billing no longer ensuring profits, an ISP’s growth now relies on rolling out new and differentiated services. However, ISPs currently do not have a well-defined architecture for rapid, cost-effective, and scalable dissemination of new services. We present iSDF, a new SDN-enabled framework that can meet an ISP’s service delivery constraints concerning cost, scalability, deployment flexibility, and operational ease. We show that meeting these constraints necessitates an SDN philosophy for a centralized management plane, a decoupled (from data) control plane, and a programmable data plane at customer premises. We present an ISP service delivery framework (iSDF) that provides ISPs a domain-specific API for network function virtualization by leveraging a programmable middlebox built from commodity home-routers. It also includes an application server to disseminate, configure, and update ISP services. We develop and report results for three diverse ISP applications that demonstrate the practicality and flexibility of iSDF, namely distributed VPN (control plane decisions), pay-per-site (rapid deployment), and BitTorrent blocking (data plane processing).

Published in: ACM SIGCOMM Computer Communication Review (Volume 44 Issue 3, July 2014)

Combined with the paper in IEEE COMST about botnet detection that was published last year, this yields a grand-total of 2 publications more than I thought would ever bear my name. In any case, my former colleagues are continuing their excellent work on the project which can be tracked at the iSDF wiki-page.

I needed to block some flows on OpenWRT from the Bro IDS. One option was to install the recent module for expiring iptables rules which sounded like an overkill. After some tinkering around I landed on using bash and at to expire the firewall rules after timeouts (luckily the at daemon was available on OpenWRT which made my job easier).

There are three parts to the process:

The bash script

First, a script which:

1. Constructs and adds the iptables rule to the FORWARD chain.
2. Constructs the corresponding deletion rule.
3. Creates a temporary bash script, writes the rule to it, makes the new script self-deleting.
4. Schedules a launch of the temporary script with at command.

Here’s the script:

#!/bin/sh
 
if [ $# -le 5 ] ; then
  echo "usage: $0 proto src sport dst dport timeout"
  exit 1
fi
 
proto=$1
src=$2
sport=$3
dest=$4
dport=$5
timeout=$6
 
echo "  proto: $1"
echo "    src: $2"
echo "  sport: $3"
echo "   dest: $4"
echo "  dport: $5"
echo "timeout: $6"
 
rule=""
 
if [ "$proto" != "any" ]; then
  rule="$rule --protocol $proto"
fi
 
if [ "$src" != "0.0.0.0" ]; then
  rule="$rule --source $src"
fi
 
if [ "$sport" != "0" ]; then
  rule="$rule --sport $sport"
fi
 
if [ "$dest" != "0.0.0.0" ]; then
  rule="$rule --destination $dest"
fi
 
if [ "$dport" != "0" ]; then
  rule="$rule --dport $dport"
fi
 
rule="$rule -j DROP"
 
echo "rule: $rule"
 
addcmd="iptables -I FORWARD $rule"
delcmd="iptables -D FORWARD $rule"
 
delscript=`mktemp`
echo "delscript: $delscript"
 
echo "#!/bin/sh" >>$delscript
echo $delcmd >>$delscript
echo "rm \"${delscript}\"" >>$delscript
chmod 755 $delscript
 
echo "adding iptable rule:"
echo $addcmd
`$addcmd`
 
atcmd="at -M -f $delscript now + $timeout min"
echo "creating at job for deletion:"
echo $atcmd
`$atcmd`

Given below is an example run. First, let’s print the default FORWARD chain:

# iptables -nL FORWARD

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             10.42.0.0/24         state RELATED,ESTABLISHED
ACCEPT     all  --  10.42.0.0/24         anywhere            
ACCEPT     all  --  anywhere             anywhere            
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Block a flow for 2 minutes:

# sh blockflow.sh tcp 50.50.50.50 50 60.60.60.60 60 2

  proto: tcp
    src: 50.50.50.50
  sport: 50
   dest: 60.60.60.60
  dport: 60
timeout: 2
rule:  --protocol tcp --source 50.50.50.50 --sport 50 --destination 60.60.60.60 --dport 60 -j DROP
delscript: /tmp/tmp.SAREJvtsK0
adding iptable rule:
iptables -I FORWARD --protocol tcp --source 50.50.50.50 --sport 50 --destination 60.60.60.60 --dport 60 -j DROP
creating at job for deletion:
at -M -f /tmp/tmp.SAREJvtsK0 now + 2 min
job 79 at Sun Jun 30 14:37:00 2013

Let’s check if the new rule was added:

# iptables -nL FORWARD

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
DROP       tcp  --  50.50.50.50          60.60.60.60          tcp spt:50 dpt:60
ACCEPT     all  --  anywhere             10.42.0.0/24         state RELATED,ESTABLISHED
ACCEPT     all  --  10.42.0.0/24         anywhere            
ACCEPT     all  --  anywhere             anywhere            
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

After 2 minutes, the temporary bash script shall remove the rule and then delete itself. To confirm:

# iptables -nL FORWARD

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             10.42.0.0/24         state RELATED,ESTABLISHED
ACCEPT     all  --  10.42.0.0/24         anywhere            
ACCEPT     all  --  anywhere             anywhere            
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

The Bro module

A simple module which exports just one function, i.e., BlockFlow::block which takes a conn_id and a count and calls the bash script with appropriate parameters:

module BlockFlow;
 
export {
  global block: function(id: conn_id, t: count);
}
 
function block(id: conn_id, t: count)
{
  print fmt("blocking %s:%d -> %s:%d for %d minutes", id$orig_h, id$orig_p, id$resp_h, id$resp_p, t);
 
  local protocol = get_port_transport_proto(id$resp_p);
  print fmt("protocol is: %s", protocol);
 
  local cmd: string = fmt("sh blockflow.sh %s %s %d %s %d %d", protocol
                                                             , id$orig_h, id$orig_p
                                                             , id$resp_h, id$resp_p, t);
  print fmt("executing: %s", cmd);
  system(cmd);
}

Bro module usage

And finally, using the module from a Bro script:

@load ./blockflow
 
event bro_init()
  {
    local id: conn_id;
    id$orig_h = 10.10.10.10;
    id$orig_p = 10/tcp;
    id$resp_h = 20.20.20.20;
    id$resp_p = 20/tcp;
    BlockFlow::block(id, 2);
  }

And the flow will be blocked for 2 minutes. Unfortunately, due to the way at command works the granularity of timeouts is limited to minutes. If you really want to block flows for only a few seconds a quick solution would be to use sleep in place of at before expiring the rule.

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 :) !

Smolt is a hardware profiler for Linux distributions which makes it easier for end-users to report back their machine configurations to a centralized database. Mike McGrath provides an excellent backend for developing Smolt GUIs which I have coupled with GTK+ for GSmolt:

(Click on the thumbnails for larger versions.)

The script can be found at the gsmolt repository on GitHub. Things on todo list include profile reporting in a separate thread and better error handling. I’ll provide RPM and Deb packages when the code is ready for a public release.

As a side note, this is the first project I have tracked using GitHub (as opposed to Launchpad + Bazaar). While Launchpad has its added advantage of PPAs which make it easier to push out public releases for Debian derivatives, I’m liking the Git experience so far. Hopefully some day Copr shall mature to a point where it can be the end-all, be-all Launchpad alternative for Fedora users.

Screensavers like glmatrix have long been used by *nixers to woo people by showing them customizable animations as desktop wallpapers. Users of desktop environments such as Xfce have to however use xwininfo to determine and use the window IDs of their desktops (as the “-root” option stops working when the root window is overlayed by respective desktop managers e.g., Xfdesktop). For those who want to automate the startup process of XScreenSaver wallpapers in such environments, here’s a quick command you can use:

$ /usr/libexec/xscreensaver/glmatrix -window-id $(xwininfo -name "Desktop" | grep 'Window id' | sed 's/.*\(0x[0-9a-z]*\).*/\1/g')

Results:

(Click on the thumbnails for larger versions.)

Over the 8 years of my acquaintance with computers valuable data has been lost at an average of twice per annum. I have tried all kinds of solution to help my situation only to fail miserably by forgetting to back up some important bits and pieces of information before upgrading my distro.

Backup solutions can mostly be factored into two approaches of archiving and cloning. If space is limited, you can archive your important data using utilities such as tar. This in fact was the approach I had been using until now. The downside appeared to be lesser accessibility of the files inside the backup. Say, I needed a small text-file from a 200 GB archive. It’d take me around 20 minutes to “get” to its location in the archive.

Which is why, I decided to shift to a newer approach. My laptop has a 320 GB hard disk and I own another 320 GB Western Digital Passport for extra data. To utilize the similitude, I bought another 500 GB Passport, transferred the “extra” data to it and then cloned the entire laptop hard disk to its 320 GB external cousin.

$ dd if=/dev/sda of=/dev/sdb

That is all. dd‘s performance was questionable, as it took around 15 hours to clone the entire 320 GB. Nevertheless, this time around I was satisfied with the final backup. Not only was it a bit-by-bit replica of my original data but also an accessible repository which I could access easily by plugging in the USB.

Few *nix users are aware of existence of one /usr/share/dict/words on their machines. The original purpose of this file was to assist Unix programs in spell-checking. Now that every program that supports typo-prevention includes its own dictionaries, the words file no longer fares as something significant in the geek universe.

Nevertheless, the nifty gem can still serve as a fun place to find or coin new words based on lexicographical constraints. The omnipresent egrep command can be used to exploit the power of regular expressions against the English dictionary. Here’s how:

• Find all words containing 6 or more characters which don’t contain any vowel, dot or dash:

  -bash-$ egrep -i '^[^aeiou.-]{6,}$' /usr/share/dict/words

  -bash-$ egrep -i '^[^aeiou.-]{6,}$' /usr/share/dict/words

  bkbndr
  BSDHyg
  BSFMgt
  BSGMgt
  BSPhTh
  crwths
  crypts
  Cynthy
  Cynwyd
  cywydd
  flybys
  Flysch
  flysch
  ftncmd
  ghylls
  glycyl
  glycyls
  glyphs
  gypsyfy
  gypsyry
  Khlyst
  Khlysts
  Khlysty
  Kylynn
  kyschty
  lymphs
  lymphy
  Lynndyl
  MSGMgt
  mtscmd
  myrrhs
  myrrhy
  Myrvyn
  Myrwyn
  nymphly
  nymphs
  pgnttrp
  Phyllys
  Phylys
  phytyl
  psychs
  pyrryl
  rhythm
  rhythms
  Schwyz
  spryly
  SSTTSS
  stddmp
  strych
  styryl
  sylphs
  sylphy
  symphysy
  synchs
  synths
  syzygy
  thymyl
  trysts
  tsktsk
  tsktsks
  tyddyn
  vyrnwy
  why’ll
  Wrycht
  WWMCCS
  xylyls

• Find all words containing exactly 4 characters which can be spelled in pure Hexspeak, e.g., 0xDEADBEEF or 0xBABEFACE:

  -bash-$ egrep -i '^[abcdef]{4}$' /usr/share/dict/words

  -bash-$ egrep -i '^[abcdef]{4}$' /usr/share/dict/words

  AAAA
  AAEE
  abac
  Abad
  Abba
  abba
  Abbe
  abbe
  abed
  ACAA
  acad
  acca
  acce
  ACDA
  aced
  Adad
  adad
  Adda
  adda
  Adee
  AFCC
  affa
  Baba
  baba
  Babb
  Babe
  babe
  BAcc
  Badb
  bade
  BAEd
  baff
  bead
  Bebe
  Bede
  bede
  Beeb
  beef
  BFDC
  caba
  Cabe
  Caca
  caca
  cace
  CADD
  Cade
  cade
  CAFE
  cafe
  caff
  CDCF
  ceca
  Cece
  cede
  CFCA
  dabb
  Dace
  dace
  Dada
  dada
  Dade
  dade
  daff
  DBAC
  dead
  deaf
  debe
  decd
  deda
  dedd
  Dede
  deed
  Eada
  Eade
  EAFB
  Ebba
  ebcd
  ECAD
  ecad
  Ecca
  ecce
  EDAC
  Edda
  edda
  Edea
  edea
  Edee
  Faba
  Fabe
  FACD
  face
  fade
  faff
  FEAF
  Febe
  feeb
  feed
  feff

• Find all words which contain ‘H’, ‘T’, ‘M’ and ‘L’ in precisely that order:

  egrep -i '^h.*t.*m.*l$' /usr/share/dict/words

  egrep -i '^h.*t.*m.*l$' /usr/share/dict/words

  haemathermal
  haematothermal
  hemathermal
  hematothermal
  hepatoumbilical
  hephthemimeral
  heptametrical
  heteroecismal
  heteromeral
  heterothermal
  hexahydrothymol
  hippotomical
  histochemical
  histomorphological
  homeothermal
  homoiothermal
  homothermal
  hydrothermal
  hygrothermal
  hyperrhythmical
  hypersentimental
  hyperthermal
  hypertridimensional
  hypostomial
  hypothermal
  hysteromaniacal

• Find all words containing ‘s’, ‘e’ and ‘x’ but at least one different character between each of them:

  -bash-$ egrep -i '^.*s[^sex]+e[^sex]+x.*$' /usr/share/dict/words

  -bash-$ egrep -i '^.*s[^sex]+e[^sex]+x.*$' /usr/share/dict/words

  antispermotoxin
  asterixis
  Asteroxylaceae
  Asteroxylon
  Cristineaux
  Erysipelothrix
  erysipelothrix
  Herstmonceux
  Hurstmonceux
  inspectrix
  Issy-les-Molineux
  Lisieux
  mesoappendix
  obstetrix
  pressure-fixing
  proces-verbaux
  salenixon
  salpingemphraxis
  salteaux
  saucebox
  sauceboxes
  sceuophylax
  scleronyxis
  scleroticonyxis
  scleroxanthin
  she-fox
  side-box
  sidebox
  Sideroxylon
  single-tax
  skeptophylaxia
  skeptophylaxis
  slipper-foxed
  smokebox
  sneakbox
  sore-pressedsore-taxed
  sore-taxed
  spectatrix
  speculatrix
  spermatoxin
  spermotoxin
  sphacelotoxin
  sphenomaxillary
  spice-box
  splanchnemphraxis
  splenauxe
  splenotoxin
  state-taxed
  stenothorax
  sternomaxillary
  sternoxiphoid
  stone-axe
  Streptothrix
  subbureaux
  sulfadimethoxine
  superaxillary
  superfix
  superfixes
  superflux
  supergalaxies
  supergalaxy
  superluxurious
  superluxuriously
  superluxuriousness
  supermaxilla
  supermaxillary
  supermixture
  superoxalate
  superoxide
  superoxygenate
  superoxygenated
  superoxygenating
  superoxygenation
  supertax
  supertaxation
  supertaxes
  sweatbox
  sweatboxes
  swine-pox
  swinepox
  swinepoxes
  Thrsieux

Now you can name your start-up company “SupErfiX” and hope that it will someday be acquired by Microsoft.

Yesterday I needed to copy the MBR of a drive over another. Googling a little I found the following command in various tutorials:

-bash-$ dd if=/dev/sda of=/dev/sdb bs=512 count=1

Where /dev/sda and /dev/sda were the original and target hard disks respectively. The command did complete its work in a snap but it also made me learn a thing about MBR structures the hard way: Only 446 bytes of the MBR contain boot code, the next 64 contain the partition table!

The implications of the lesson being, if partition tables of both hard disks differ — which unfortunately was the case with me — the partition table of the target hard-disk will be overwritten. The correct way would therefore be:

-bash-$ dd if=/dev/sda of=/dev/sdb bs=446 count=1

In case you did mess up the table, I recommend TestDisk for recovering your partitions.