Linux Weekly News

Over on the Red Hat Developer site, David Malcolm has an article about improvements in GCC 15, specifically focusing on the diagnostic information that the compiler emits. This includes ASCII art with a "⚠️" warning emoji to display the execution path when it detects a problem (like an infinite loop in one of his examples), better C++ template errors, machine-readable diagnostics using Static Analysis Results Interchange Format (SARIF), better messages regarding C23 compatibility since that is the default C version for GCC 15, and more. Since the changes are focused on messages, there is the inevitable color-scheme update as well: GCC will use color when emitting its text messages on stderr at a suitably modern terminal, using a few colors that seem to work well in a number of different terminal themes—but the exact rules for choosing which color to use for each aspect of the output have been rather arbitrary.

For GCC 15, I've gone through C and C++'s errors, looking for places where two different things in the source are being contrasted, such as type mismatches. These diagnostics now use color to visually highlight and distinguish the differences.

Compute Express Link (CXL) memory is not like the ordinary RAM that one might install into a computer; it can come and go at any time and is often not present when the kernel is booting. That complicates the management of this memory. During the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, Gregory Price ran a session on the challenges posed by CXL and how they might be addressed.

Greg Kroah-Hartman has announced the release of eight stable kernels: 6.14.2, 6.13.11, 6.12.23, 6.6.87, 6.1.134, 5.15.180, 5.10.236, and 5.4.292. These all contain a large assortment of important kernel fixes throughout the tree.

The Data Access MONitor (DAMON) subsystem provides access to detailed memory-management statistics, along with a set of tools for implementing policies based on those statistics. An update on DAMON by its primary author, SeongJae Park, has been a fixture of the Linux Storage, Filesystem, Memory-Management, and BPF Summit for some years. The 2025 Summit was no exception; Park led two sessions on recent and future DAMON developments, and how DAMON might evolve to facilitate a more access-aware memory-management subsystem in the future.

Security updates have been issued by AlmaLinux (tomcat and webkit2gtk3), Debian (chromium), Fedora (ghostscript), Mageia (atop, docker-containerd, and xz), Red Hat (go-toolset:rhel8), SUSE (apache2-mod_auth_openidc, apparmor, etcd, expat, firefox, kernel, libmozjs-128-0, and libpoppler-cpp2), and Ubuntu (dino-im, linux, linux-aws, linux-aws-hwe, linux-azure, linux-azure-4.15, linux-gcp, linux-gcp-4.15, linux-hwe, linux-kvm, linux-oracle, linux, linux-aws, linux-kvm, linux-lts-xenial, linux-fips, linux-fips, linux-aws-fips, linux-azure-fips, linux-gcp-fips, opensc, and poppler).

Inside this week's LWN.net Weekly Edition:

• Front: Debian project leader election; 6.15 Merge window; Lots of LSFMM coverage; Joplin.
• Briefs: Firefox hardening; OpenSSH 10.0; Supply chain security; FreeDOS 1.4; OpenSSL 3.5.0; Rust 1.86.0; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

Tom Schuster, Frederik Braun, and Christoph Kerschbaumer have published an article on the Firefox Security team's Attack & Defense blog that explains recent work to harden Firefox's frontend code.

We have rewritten over 600 JavaScript event handlers to mitigate XSS and other injection attacks in the main Firefox user interface. This mitigation will ship in Firefox 138. However, blocking the execution of scripts in the parent process is not the end - we will expand this technique to other contexts in the near future. There is still more work to do as the UI requires JavaScript APIs with a high level of privileges. However: We still eliminated a whole class of attacks, significantly raising the bar for attackers to exploit Firefox.

In a combined storage and filesystem track session at the 2025 Linux Storage, Filesystem, Memory Management, and BPF Summit, John Garry continued the theme of "untorn" (or atomic) writes that started in the previous session. It was also an update on where things have gone for untorn writes since his session at last year's summit. Beyond that, he looked at some of the plans and challenges for the feature in the future.

Four candidates have stepped up to run in the 2025 Debian Project Leader (DPL) election. Andreas Tille, who is in his first term as DPL, is running again. Sruthi Chandran, Gianfranco Costamagna, and Julian Andres Klode are the other candidates running for a chance to serve a term as DPL. The campaigning phase ended on April 5, and Debian members began voting on April 6. Voting ends on April 19. This year, the campaign period has been lively and sometimes contentious, touching on problems with Debian team delegations and finances.

The 6.15 merge window saw the inclusion of a new type of lock for BPF programs: a resilient queued spinlock that Kumar Kartikeya Dwivedi has been working on for some time. Eventually, he hopes to convert all of the spinlocks currently used in the BPF subsystem to his new lock. He gave a remote presentation about the design of the lock at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF summit.

Tiered-memory systems feature multiple types of memory with varying performance characteristics; on such systems, good performance depends on keeping the most frequently used data in the fastest memory. Identifying that data and placing it properly is a challenge that has kept developers busy for years. Bharata Rao, presenting remotely during a memory-management-track session at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, led a discussion on a potential solution he has recently posted; Raghavendra K T was also named on the session proposal. It seems likely, based on the discussion, that developers working in this area will not run out of problems anytime soon.

The kernel samepage merging (KSM) subsystem works by finding pages in memory with the same contents, then replacing the duplicated copies with a single, shared copy. KSM can improve memory utilization in a system, but has some problems as well. In two memory-management-track sessions at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, Mathieu Desnoyers and Sourav Panda proposed improvements to KSM to make it work better for specific use cases.

OpenSSH 10.0 has been released. Support for the DSA signature algorithm, which was disabled by default beginning in 2015, has been removed. Other notable changes include using the post-quantum algorithm mlkem768x25519-sha256 for key agreement by default, support for systemd-style socket activation in Portable OpenSSH, and moving code for user authentication from the sshd-session binary to the new ssh-auth binary:

Splitting this code into a separate binary ensures that the crucial pre-authentication attack surface has an entirely disjoint address space from the code used for the rest of the connection. It also yields a small runtime memory saving as the authentication code will be unloaded after the authentication phase completes. This change should be largely invisible to users, though some log messages may now come from "sshd-auth" instead of "sshd-session". Downstream distributors of OpenSSH will need to package the sshd-auth binary.

The release notes also warn that "software that naively matches versions using patterns like "OpenSSH_1*"" may be confused by the new version number.

Security updates have been issued by Debian (lemonldap-ng, libbssolv-perl, and phpmyadmin), Fedora (augeas, mariadb10.11, and thunderbird), Oracle (gimp, libxslt, python3.11, python3.12, tomcat, and xorg-x11-server), Red Hat (expat, grafana, opentelemetry-collector, and webkit2gtk3), SUSE (azure-cli-core, doomsday, kernel, and poppler), and Ubuntu (dotnet8, dotnet9, erlang, and poppler).

Version 3.5.0 of OpenSSL has been released. This release adds support for server-side QUIC (RFC 9000), a new configuration option (no-tls-deprecated-ec) that disables support for TLS groups deprecated in RFC 8422, and more.

Version 1.4 of FreeDOS has been released. This is the first stable release since 2022, and includes improvements to the Fdisk hard-disk-management program, and reliability updates for the mTCP set of TCP/IP applications for DOS.

This version was much smoother because Jerome Shidel, our distribution manager, had an idea after FreeDOS 1.3 that we could have a rolling test release that collected all of the changes that people make over time. Previous to this, each new FreeDOS distribution (like 1.0, 1.1, 1.2, and 1.3) required bundling up packages into a "release candidate," and we would go through several iterations of updating the release candidates.

Jerome's method of building the FreeDOS distribution made it easier to automate a test release, which we decided to update every month. As the test releases accumulated enough changes to warrant a release, we could then make the next test release a "release candidate" which would iterate to the next version of the FreeDOS distribution. Since 2022, we've released monthly test releases. Thanks Jerome!

LWN covered FreeDOS last year for its 30th anniversary.

Joplin is an open-source note-taking application designed to handle taking many kinds of notes, whether it is managing code snippets, writing documentation, jotting down lecture notes, or drafting a novel. Joplin has Markdown support, a plugin system for extensibility, and accepts multimedia content, allowing users to attach images, videos, and audio files to their notes. It can provide synchronization of content across devices using end-to-end encryption, or users can opt to stick to local storage only. Joplin even offers a command-line version for terminal-based usage. Joplin 3.2, the most recent feature release, brought long-awaited multi-window support, multi-column layouts, enhanced accessibility, and theme detection.

Quite a bit of work has been done in recent years to allow the kernel to make more use of large folios. That progress has not yet reached the handling of text (executable code) areas, though. During the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, Ryan Roberts ran a session on how that situation might be improved. It would be a relatively small and contained operation, but can give a measurable performance improvement.

The kernel makes extensive use of per-CPU data as a way to avoid contention between processors and improve scalability. Using the same technique in user space is harder, though, since there is little control over which CPU a process may be running on at any given time. That hasn't stopped Mathieu Desnoyers from trying, though; in the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, he presented a proposal for how user-space per-CPU memory could work.

Security updates have been issued by AlmaLinux (gimp, libxslt, python3.11, python3.12, and tomcat), Debian (ghostscript and libnet-easytcp-perl), Fedora (openvpn, perl-Data-Entropy, and webkitgtk), Red Hat (python-jinja2), SUSE (giflib, pam, and xen), and Ubuntu (apache2, binutils, expat, fis-gtm, linux-azure, linux-azure-6.8, linux-nvidia-lowlatency, linux-azure, linux-azure-fde, linux-azure-5.15, linux-azure-fde-5.15, linux-azure-fips, linux-gcp-fips, linux-hwe-5.4, linux-nvidia, linux-nvidia-tegra-igx, ruby2.7, ruby3.0, ruby3.2, ruby3.3, and vim).