Archive for the ‘Uncategorized’ Category

Sysreq on Lenovo x250

May 24, 2017

I sometimes find myself in the situation that I need magic sysreq on my machine. Especially when running the development version of Ubuntu it is sometimes useful to do the magic “sync,umount,boot” sequence.

The new Lenovo keyboards do not have a dedicated sysreq key anymore. But after some searching and fiddling I is possible to emulate the behaviour:

Press “Fn”+”Ctrl”+”Alt”+”s” all at the same time. Then release “Fn”+”s” but keep “Ctrl”+”Alt” pressed. The keys you press next (while keeping “Ctrl”+”Alt” pressed) are now the systreq keys. So e.g. when pressing “s” next (while keeping “Ctrl”+”Alt” pressed) the system will do a emergency sync, pressing “u” next (while keeping “Ctrl”+”Alt” pressed) will do the emergency umount etc.

This should also work on any of the “new” Lenovo keyboard.

Booting the samsung 840 SSD firmware update iso from grub2

December 13, 2015

In order to apply a firmware update for my Samsung 840 SSD I had to boot an iso image with the firmware updater. My laptop does not have an optical drive so I decided to to use my grub2 and it’s loopback support.

So I added to

/etc/grub.d/40_custom

the following lines:

menuentry "firmware" {
  set isofile="/boot/ssd840.iso"
  loopback loop (hd0,1)$isofile
  legacy_kernel (loop)/isolinux/memdisk (loop)/isolinux/memdisk
  legacy_initrd (loop)/isolinux/btdsk.img
}

This works quite well. The firmware update process itself is a bit of a pain. At the end it asked to power cycle the SSD. Which is pretty much impossible because it is inside my laptop. After I continued without power-cycling the drive it warned me that applying failed. However that is a false scary message. After power off and power on of the laptop the firmware update was applied.

Passhash sha512crypt

November 28, 2015

I added sha512crypt support to the PassHash firefox extension a while ago to make attacking PassHash even more difficult. It uses the glibc 5000 rounds default. If you happen to use PassHash you should consider upgrading to this schema.

PassHash sha512 support

June 9, 2013

I added sha512 support to the PassHash firefox extension here (and added pull request to get it into the upstream branch). I felt its important to do this after reading this article.

ansible ad-hoc data gathering

June 1, 2013

When using ansible and its “setup” module to gather ad-hoc facts-data about multiple hosts, remember that it runs the jobs in parallel which may result in out-of-order output. With “ansible -f1” the number of parallel processes can be limited to one to ensure this won’t happen. E.g.:

$ ansible all -f1 -m setup -a filter=ansible_mounts

(the filter argument for the facts module is also a nice feature).

git fast-import apt

May 16, 2013

Due to popular demand I moved debian apt and python-apt from bzr to git today. Moving was pretty painless:

$ git init
$ bzr fast-export --export-marks=marks.bzr -b debian/sid /path/to/debian-sid | git fast-import --export-marks=marks.git

And then a fast-import for the debian-wheezy and debian-experimental branches too. Then a

$ git gc --aggressive

(thanks to Guillem Jover for pointing this out) and that was it.

The branches are available at:

Webkitgtk & SSL

April 30, 2013

For a project of mine I created a small app based on webkitgtk that talks to a SSL server.

And I almost forgot about the libsoup default behavior for SSL certificates checking. By default libsoup and therefore webkitgtk will not do any SSL certificate checks. You need to put something like the following snippet into your code (adjust for your language of choice):

from gi.repository import WebKit

session = WebKit.get_default_session()
session.set_property("ssl-use-system-ca-file", True)

If you don’t do this it will accept any certificate (including self-signed ones).

This is documented behavior in libsoup and they don’t want to change it for compatiblity reasons in libsoup. But for webkit its unexpected behavior (at least to me) and I hope the webkitgtk developers will consider changing this default in webkit. I filed a bug about it. So if you use webkitgtk and SSL, remember to set the above property.

PassHash cmdline

April 18, 2013

I use the PassHash firefox extension to generate site-specific strong passwords. The idea behind the extension is that a master password and a siteTag (e.g. the domain name) is used to generate a sha1 hash. This hash is used as the password for the website. In python its essentially this code:

h = hmac.new(master_pass, site_tag, hashlib.sha1)
print(b64encode(h.digest())[:hash_len])

I want a commandline utility that can output me PassHash compatible hashes when I use w3m (or if the extension stops working for some reason).

To my delight I discovered that the upstream git repNice and hard to brute-force.o of PassHash already has a python helper to generate passhash compatible password. I added some tweaks to add pythons argparse [1] and now I’m really happy with it:

$ ./tools/passhash.py --hash-size 14 slashdot.org
Please enter the master key: 
KPXveo7bq7j1%X

Hard to brute-force and matches what the extension generates.

squid-deb-proxy for Debian

April 11, 2013

I uploaded squid-deb-proxy into Debian unstable today and its in the NEW queue. I created it back in the days of Ubuntu 10.04 and some people voiced interest in having it in Debian as well so I spend a bit of time to get it customized for Debian.

Squid-deb-proxy uses the well known squid proxy with a custom configuration to cache deb package and Indexfiles (like Packages.gz) that will allow caching from the default archives and mirrors and reject anything else by default.

The basic philosophy is that “it just works”. You run on your server:

root@server# apt-get install squid-deb-proxy

and on your clients:

root@client# apt-get install squid-deb-proxy-client

and that’s it. It does not require any fiddling with configuration (unless you want to 😉 ). The default will let you connect to .debian.org and nothing else.

The server will announce itself via avahi as _apt_proxy._tcp and the
client will hook into apt to use Acquire::http::ProxyAutoDetect. The
client is useful for other servers that announce themself via avahi.

Packaging was a bit more work than anticipated because there is a bit of setup and teardown work in the initscript. For Debian as sysvinit script was needed, Ubuntu uses upstart so it took a bit of refactoring to extract the code into a common helper.

If you want to try it now, its available via:

$ bzr branch lp:squid-deb-proxy
$ cd squid-deb-proxy
$ bzr-buildpackage

and in unstable once it leaves the NEW queue.

Fun with sqlite/fts

March 27, 2013

A while ago I played with sqlite. Its pretty awesome. When using the full text search (fts) extension it also provides super fast full text searching. One of the things I was missing (compared to other engines) is the similar text suggestion (“Did you mean?”) support. Fortunately this is relatively easy to add via the fts4aux virtual table that sqlite supports.

I pushed a full example of to https://github.com/mvo5/sqlite-fts-did-you-mean. The way it works is that you build a set of similar words and use that to query for the “term” value from the fts4aux table.

Here is the output from the example:

$ ./fts_did_you_mean.py aptx
Did you mean:
 apex (rank: 2)
 apt (rank: 1)
time 0.024138927459716797