Linux Weekly News

The 7.2-rc4 kernel prepatch is out for testing. Linus said: "This whole week I had the feeling that people were starting to go on summer vacation, but running the numbers shows that I must have been wrong - it all looks pretty normal."

Adrian Mastronardi has released a book called Half a Second; it is a detailed look into the XZ backdoor attempt of 2024. The book is freely available under a (non-free) noncommercial, no-derivatives CC license.

Half a Second tells that story as one continuous narrative: the burned-out volunteer who maintained the code alone and was patiently, expertly manipulated into giving it up; the engineer whose half-second of curiosity caught the attack through a chain of luck and hard-won instinct; and the operator who built it, who has never been identified and, this book argues, may never be.

The 7.1.4, 6.18.39, and 6.12.96 stable kernel updates have been released; each contains a fairly large set of important fixes.

Collabora has published a blog post about its work with Valve on Holo Core, which is a port of Arch Linux to aarch64 to be used as the the operating system on Valve's 64-bit Arm Steam Frame gaming system. Collabora has released the sources, binary packages, and a container image for aarch64 devices. The post describes some of the challenges in porting Arch Linux to a new architecture, and what remains to be done:

Whilst the infrastructure developed to this point is capable of building from first principles up until a point-in-time snapshot, the next step is to build this into a system which can track Arch Linux as it is developed. This work will serve as the basis of a continuously-operating CI system capable of shadowing Arch Linux itself. We will work with the upstream Arch Linux project to help Arch with their efforts to port the distribution to aarch64 architecture and work towards automated repeatable builds.

The post also includes instructions on how to create and test an aarch64 build container on an x86_64 host, for users who would like to follow along at home but lack a 64-bit Arm device.

Since 2020, BPF programs have been able to act as Linux security modules (LSMs). Several projects, including systemd, have been working to use that capability to provide more security to users. Christian Brauner spoke at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit about some of the limitations of using BPF in this way, and the changes he would like to see for systemd's use. In particular, he would like a way to make sure that BPF programs cannot be removed or have their private data tampered with.

Security updates have been issued by AlmaLinux (cifs-utils, container-tools:rhel8, libreoffice, nodejs:24, perl-XML-LibXML, and python3.12), Fedora (ansible-collection-ansible-posix, firefox, freerdp, ImageMagick, mingw-glib2, perl-DBI, perl-HTTP-Date, rust-cargo-rpmstatus, and rust-opendal), Oracle (cifs-utils, gegl, gimp, git-lfs, go-toolset:ol8, hplip, kernel, libreoffice, maven:3.9, perl-XML-LibXML, python3, python3.12, python3.9, and uek-kernel), Red Hat (kernel, kernel-rt, and podman), Slackware (netatalk), SUSE (agama, aws-nitro-enclaves-binaryblobs-upstream, gimp, gpsd, grafana, hostapd, ImageMagick, jackson-databind, kernel, libssh2_org, nm-configurator, opennlp, perl-Mojolicious, python-Pillow, python-python-engineio, python-python-socketio, and tomcat11), and Ubuntu (ntfs-3g, python-authlib, ruby2.3, tar, and ubuntu-advantage-tools).

The extensible scheduler class (sched_ext) allows the installation of custom CPU schedulers as a set of BPF programs. While sched_ext, in its current form, has already led to a lot of interesting scheduler-development work, the subsystem itself is still undergoing rapid evolution. Among other work, the ability to set up a hierarchy of sub-schedulers is approaching completion, and a longstanding incompatibility with proxy execution is coming to an end.

Security updates have been issued by AlmaLinux (cups, git-lfs, kernel, libsolv, libxml2, python3.12, and python3.9), Debian (chromium, dhcpcd5, and ntfs-3g), Fedora (firefox, perl-Imager, python-bcrypt, python-tiktoken, roundcubemail, and xrdp), Mageia (openssl, poppler, python-mistune, and tmux), Oracle (389-ds-base, cups, git-lfs, glibc, host-metering, kernel, libsolv, libxml2, nginx:1.24, PackageKit, python-pillow, and qemu-kvm), Red Hat (buildah, containernetworking-plugins, and skopeo), SUSE (buildah, cosign, curl, distribution, dnsmasq, glib-networking, glibc, gnutls, gstreamer-plugins-bad, ImageMagick, kernel, podman, python-cryptography, python313-django-debug-toolbar, rekor, sccache, sssd, and yelp), and Ubuntu (dotnet8, dotnet10, libslirp, luajit, python-idna, sympa, and tomcat8).

Inside this week's LWN.net Weekly Edition:

• Front: Fighting scraper bots; io_uring queues; Filesystem testing; BPF shielding; Sending packets from BPF; Kitty; QBE.
• Briefs: Shim security; seunshare vulnerability; Debian bookworm; Rust 1.97.0; Linux.org; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

It should come as no surprise that a gathering of filesystem developers would discuss filesystem testing; it has been a mainstay of the Linux Storage, Filesystem, Memory Management, and BPF Summit over the years and the 2026 summit was no exception. Ted Ts'o led the discussion this time; he had a few different topics to raise, including his perception of increasing regressions for ext4 in the stable kernels and what can be done to help reduce them. As with other similar sessions at the summit over the years, there is a lot of interest in collaborating on test inputs and outputs, but finding a way to centralize that information has so far eluded the filesystem community.

The SUSE Security Team Blog has a post with an analysis of seunshare, which is used by SELinux to confine untrusted programs. During a review of version 3.10 of the program, the team identified two local Denial-of-Service (DoS) vectors.

Since seunshare is supposed to run on SELinux-enabled systems, it is important to understand what kind of privilege escalation can be achieved when vulnerabilities are exploited in a setuid-root binary like this. Many SELinux-enabled systems, such as Fedora and openSUSE, ship with the "targeted" SELinux policy by default. This policy is focused on confining well-known system services, but assigns an unconfined SELinux context to interactive users by default to achieve a balance between security and usability.

There is currently no domain transition from the unconfined domain to the more restricted seunshare_t defined in the SELinux policy for seunshare. This means the execution of seunshare continues in the unconfined domain. Thus in the context of attacks carried out by interactive users, the impact of the vulnerabilities below will be a root-like privilege escalation despite the system running in SELinux enforced mode.

See the post for the full write-up of the team's discoveries and timeline. The vulnerabilities have been fixed in version 3.11.

Processes that use io_uring tend to keep a lot of balls in the air; being able to have many operations underway at any given time is part of the point of that API in the first place. The io_uring subsystem must, as a result, keep track of a lot of tasks that have to be performed at the right time. In current kernels, io_uring uses a standard kernel linked-list primitive to track those work items. As of the 7.2 kernel release, though, io_uring will, instead, use a new lockless, multi-producer, single-consumer (MPSC) queue, resulting in some notable performance gains. Lockless algorithms tend to be tricky, but the one used here is relatively approachable and shows how these algorithms can work.

Security updates have been issued by AlmaLinux (cifs-utils, corosync, cups, freerdp, git-lfs, go-fdo-client and go-fdo-server, go-toolset:rhel8, kernel, kernel-rt, libinput, libxml2, nginx:1.24, openssl, pacemaker, perl-DBI:1.641, php8.4, python-pillow, python3, and python3.12), Debian (grub2, libxfont, opam, and wolfssl), Fedora (freerdp, kernel, and prometheus), Mageia (imagemagick), Oracle (buildah, freerdp, gimp, kernel, nginx, openexr, openssl, perl-DBI, podman, vim, xorg-x11-server, and xorg-x11-server-Xwayland), Red Hat (python3.12), SUSE (afterburn, buildah, busybox, enc, freetype2-devel, go1.25, go1.25-openssl, go1.26-openssl, gosec, grafana, helm, krb5, kubernetes-old, libopenbabel8, libxml2, libxml2-16, nasm, openssl-3, patch, python-Authlib, python-mistune, python-soupsieve, python-sqlparse, python3-dulwich, python313-Pillow, rootlesskit, sbootutil-1, tomcat, and tomcat11), and Ubuntu (alsa-lib, dnsmasq, gnutls28, libheif, linux-aws, linux-fips, linux-lts-xenial, linux-gcp-5.15, linux-intel-iotg-5.15, linux-hwe-6.17, linux-raspi, mariadb, openvpn, python-httplib2, vim, and wget).

The CMU CERT Coordination Center has put out an advisory that many exploitable versions of the shim binary, used to boot Linux on systems with UEFI secure boot enabled, were never added to the revocation list.

An attacker with administrative privileges or the ability to modify the boot process could use one of the vulnerable shim bootloaders to bypass Secure Boot protections and execute arbitrary code before the operating system loads. Code executed during this early boot phase may achieve persistent compromise of the platform, including the ability to load unsigned or malicious kernel components that can survive system reboots and, in some cases, operating system reinstallation.

The advisory contains a list of vulnerable shims.

Rob Kennedy has posted the story of the birth of Linux.org — one of the earliest Linux-related web sites — and its more recent rebirth.

The site was founded in May 1994 by Michael McLagan, at a time when Linux itself was barely three years old. Linus Torvalds had only just released it to the world, there was no real way for a newcomer to find their footing, no search engines, no Wikipedia, none of the infrastructure people take for granted now for figuring out a new piece of technology. Michael built linux.org to fill that gap, a place for people to learn about Linux and follow the movement as it grew.

The Maintainers Summit is an annual, invitation-only gathering of kernel developers and maintainers to discuss development-process issues; see LWN's 2025 Maintainers Summit coverage for an example. The call for topics for the 2026 gathering (Prague, October 8) has gone out. One of the best ways to obtain an invitation to the Summit is with a good topic proposal. For best consideration, topics should be submitted before July 24.

Tetragon, the BPF-based security monitoring tool, uses BPF to monitor different aspects of a running kernel and enforce user-specified policies. It sends its data to a user-space process, which forwards the data to a central monitoring service elsewhere in the network, however. This presents a point of vulnerability: if an attacker can kill Tetragon's user-space agent, it won't be able to properly report on the situation. Song Liu, Mahé Tardy, and Liam Wiseheart spoke about their work removing the need for the user-space agent at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit.

Security updates have been issued by AlmaLinux (389-ds:1.4, buildah, freeipmi, freerdp, gegl, gimp, golang, kernel, libreoffice, maven:3.9, openexr, perl-DBI, plexus-utils, podman, tomcat, tomcat9, xorg-x11-server, and xorg-x11-server-Xwayland), Debian (imagemagick, p7zip, and redis), Fedora (breezy, calibre, and golang-github-openprinting-ipp-usb), Mageia (ffmpeg, gzip, haproxy, libheif, libtiff, libxml2, packages, perl-List-SomeUtils-XS, and perl-Socket), SUSE (alsa, chromedriver, curl, dhcpcd, docker-compose, glibc, haproxy, ImageMagick, jq, kernel, kubernetes, libpng15, libredwg-devel, libslirp, nghttp2, php8, python-Pillow, python313-Django, python313-weasyprint, qemu, rust-keylime, sccache, and systemd), and Ubuntu (cifs-utils, libexif, libreoffice, libssh2, openssh, and pipewire).

Cisco has some unusual challenges when it comes to deploying security patches across the company's many devices running custom kernels. John Fastabend spoke about his work preventing exploits with BPF at the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit. The technique could substantially reduce the time necessary to respond to kernel vulnerabilities, but it will not be fully effective unless more hooks are added to the kernel.

Debian has announced the final normal update for Debian 12 ("bookworm"). Long-term-support updates will continue until 2028. As may be expected from a stable version, the update is mostly limited to security fixes. Still, it may be time for Debian users to look into upgrading to a more recent version. Conveniently, Debian 13 ("trixie") also received an update this weekend, with many of the same security fixes.