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XZ Backdoor in SSH Background Someone planted a backdoor in XZ compression, which is believed to affect SSH. More details can be found. Although it was never shipped to production version of any distro. Even if you are using unaffected version I suggest you defuse any similar backdoors. https://www.openwall.com/lists/oss-security/2024/03/29/4 https://news.ycombinator.com/item?id=39865810 https://gist.github.com/thesamesam/223949d5a074ebc3dce9ee78baad9e27 https://www.redhat.com/en/blog/urgent-security-alert-fedora-41-and-rawhide-users The Kill Switch The backdoor has a kill switch, it does not activate if it detects that someone is observing it (debugger attached...etc). An easy way to defuse the backdoor is to just define TERM environment variable causing the backdoor to think it's being observed and it would disable itself hopefully this is not specific to this backdoor but any similar one.  mkdir /etc/systemd/system/sshd.service.d/ echo -e "[Service]\nEnvironment=TERM=xt...

Introduction This weekend I've made a GTK+ application, I've done my best to make it responsive by applying my old Android development experience. Android make it clear that you should not block UI thread (main thread) not non-UI tasks like: disk IO (read a file) network IO (request remote API) internal SQLite database intensive computations  Let me quote : "You should not perform the work on the UI thread, but instead create a worker thread and do most of the work there." private class MyTask extends AsyncTask... { protected Long doInBackground(URL... urls) { // worker thread } protected void onProgressUpdate(Integer... progress) { // ui thread } protected void onPostExecute(Long result) { // ui thread } } GTK+ GTK+ is not threadsafe, in the sense all calls to GTK+ should be from a single thread that is the main thread or the UI thread, which seems similar to Android. We have a class that loads the glade XM...

Back in my first days of Linux I had a bootable floppy disk with fully functional Linux distro (a kernel, a shell and busybox tools and lua scripting). Maybe that was not much, but it was less than 2MB and would work on an old 386 PC with 4MB of RAM. But shell is boring, graphical minimal Linux distros was several hundreds of mega bytes and need hundreds of MB of RAM. Embedded devices typically have a minimal Linux with busybox or alike running with no graphical interface but instead they have some sort of web interface exposed to some port. If you tried to run a minimal graphical Linux distro let's say XFCE on an embedded device (let's say a raspberry pi) you would notice that most of its limited resources are taken by Xorg the legacy graphical server. Introducing Wayland Wayland is a new different approach to graphical interface, instead of sending drawing instruction over a legacy protocol (with so many extensions) to a legacy daemon (with so many extensions) that ...

Introduction Kubernetes had won the container orchestration war. Here is a summary of its features. It's an API, command line and UI. It uses etcd to keep its state. Every thing is done via Yaml or JSON (your choice). General Node : a machine or instance (used to be called "minion") Namespace: a grouping of resources Label: a tag applied to a resource ex. role=frontend Annotations: another form of meta data  Workloads Container  ( spec ) : the building block of deployable service or runnable task using linux containers ex. docker image and params to pass at runtime. Typically created in a Pod see below Pod  ( spec ) : one of more containers scheduled to nodes together and thus can share volumes. Most common pods have a single container but there are use cases for more (ex. nginx and php-fpm) . If you replicate a pod to have 3 replicas it would have 3 nginx and 3 php-fpm. If php-fpm created a file in the volume, nginx can see it. Typically cr...

Introduction Alpine Linux is a minimal distro with package manager ( APK ) that is based on busybox and musl library . Like the  CirrOS , it's very lightweight, but unlike it, it's full featured. In case you don't know me, my Linux distro of choice is Fedora/CentOS, in this post I'm going to bootstrap a QCow2 cloud image of Alpine Linux on my distro of choice. Using docker to bootstrap a working chroot Type mkdir alpine35-root docker run --rm -ti -v $PWD/alpine35-root:/data alpine:3.5 apk --arch x86_64 -X http://nl.alpinelinux.org/alpine/v3.5/main/ -U --allow-untrusted --root /data --initdb add alpine-base  and you should get a line like this OK: 6 MiB in 16 packages so now we have a working alpine chroot in the directory alpine35-root Creating Bootable QCoW2 Image Because I don't want to format my hard disk by mistake and because I know Murphy's law, I'll take those 6MB as tarball and continue on a VM. dd if=/d...

Instructions let's save a text file named "test.sh" having the following content #! /bin/bash for i in `seq 50` do    echo $i    sleep 1 done it just print number from 1 to 50 second by second (you can change 50 to any number) now as regular user type chmod +x ./test.sh systemd-run --user --unit=my-test ./test.sh  the above command will run the script as a user service called my-test at any time you can trace it with systemctl and see the logs using journalctl like this journalctl -ln 100 -f --user-unit=my-test systemctl --user status my-test you can abort it using systemctl --user stop my-test Use cases Let's assume you have a web interface that trigger something and you want to trace it later just make your unprivileged web application (written in php/python and running as regular non-root user) called "systemd-run --user" and query the status and follow the logs using systemctl and jou...

Introduction If you are familiar with docker then you are going to love this little hack. UNC  is a tool to demonstrate how to launch containers without being root. Getting the code and compiling it git clone https://github.com/LK4D4/unc.git cd unc mkdir -p gopath/src/ ln -s ../.. gopath/src/unc export GOPATH=$PWD/gopath cd gopath/src/unc go get go build cd unet go build cd .. sudo cp unc unet/unet /usr/local/bin/ sudo chmod u+s /usr/local/bin/unet What is SetUID for? "unet" is a tool used "unc" that creates veth pairs and assign one of them to container. Root user (via setuid) is needed to be able to assign a network interface for the user container. Creating some minimal root filesystems sudo dnf install busybox # as regular unprivileged user type mkdir -p roots/busybox1/{bin,sbin,proc,dev,etc} cp /sbin/busybox roots/busybox1/sbin/ echo "root:x:0:0:root:/root:/bin/bash" > roots/busybox1/etc/passwd echo "r...

UPDATE: docker inc. addressed those concerns by donating its runtime to Cloud Native Computing Foundation  (CNCF) and by making moby a community project. Yes, I'm  claiming that Docker is just a hyped vendor lock-in. Don't get me wrong, Linux containers, micro-services, DevOPs,... are all very cool and they are cool for a reason. On the other hand docker is just an overrated vendor lock-in. Linux containers is a new term for old technologies like namespace and control groups, used in production maybe for more than a decade. LXC is one way to access those kernel feature in a boring way. OpenVZ and the newly hyped LXD is virtualization hypervisor based on Linux containers. SystemD do use containers for all of spawned services and can be used to spawn containers (using nspawn ). In other words Docker did not invent containers. I was warned about that more than a year ago but then it was not that obvious. What's wrong with docker? So many things! At every sing...

Python provides a base socket server that got no concurrency support by default, which can be used to create any server including HTTPServer or WSGI applications servers like the wsgiref. You can plugin concurrency support using ThreadingMixIn or ForkingMixIn   this would allow our pure-python server to handle multiple requests by forking another process or starting a new thread while the main thread in the main process keeps accepting requests. In this post I'm going to introduce my own PooledProcessMixIn and its features over other solutions. The concept of Pool BSD mascot with a fork I've taken a look at the code of those Mix-Ins and found serious performance issue with it as they allocate a new process or new thread each time a request comes to the server. Beside delaying the response waiting for the allocation, it's an open-ended approach (no re-using of those threads or processes). The pool approach is to allocate a number of threads or fork a number of pr...