Linux Weekly News

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).

Pahole (originally "Poke-a-hole") is a Swiss Army knife for exploring and editing debug information. Pahole is also currently involved in the kernel's build process to rearrange the information produced by various compilers into a form useful to the BPF verifier, although there are plans to render it unnecessary. Pahole maintainer Arnaldo Carvalho de Melo shared some status updates about the project at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit. Interested readers can find his slides here.

ACM Queue looks at the security problem in the light of a report on Multics security that was published in 1974.

We are all struggling with a massive shift that has happened in the past 10 or 20 years in the software industry. For decades, software reuse was only a lofty goal. Now it's very real. Modern programming environments such as Go, Node, and Rust have made it trivial to reuse work by others, but our instincts about responsible behaviors have not yet adapted to this new reality.

The fact that the 1974 Multics review anticipated many of the problems we face today is evidence that these problems are fundamental and have no easy answers. We must work to make continuous improvements to open source software supply chain security, making attacks more and more difficult and expensive.

The kernel's swap subsystem is complex and highly optimized — though not always optimized for today's workloads. In three adjacent sessions during the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, Kairui Song, Nhat Pham, and Usama Arif all talked about some of the problems that they are trying to solve in the Linux swap subsystem. In the first two cases, the solutions take the form of an additional layer of indirection in the kernel's swap map; the third, which enables swap-in of large folios, may or may not be worthwhile in the end.

Linus Torvalds released 6.15-rc1 and closed the 6.15 merge window on April 6. By that time, 12,633 non-merge changesets had found their way into his repository; that is substantially more than were merged during the entire 6.14 development cycle. Just under 6,000 of those changesets were merged after the first-half merge-window summary was written.

The 6.14.1, 6.13.10, 6.12.22, 6.6.86, and 6.1.133 stable kernels have all been released. They contain a relatively small collection of important fixes across the kernel tree.

Security updates have been issued by Debian (abseil, atop, jetty9, ruby-saml, tomcat10, trafficserver, xz-utils, and zfs-linux), Fedora (chromium, condor, containernetworking-plugins, cri-tools1.29, crosswords-puzzle-sets-xword-dl, exim, ghostscript, matrix-synapse, upx, varnish, and yarnpkg), Gentoo (XZ Utils), Mageia (augeas, corosync, nss & firefox, and thunderbird), Oracle (container-tools:ol8, firefox, freetype, and kernel), Red Hat (firefox), SUSE (chromium, gn, firefox-esr, go1.23-1.23.8, go1.24, go1.24-1.24.2, google-guest-agent, govulncheck-vulndb, gsl, python311-ecdsa, thunderbird, and webkit2gtk3), and Ubuntu (kamailio, libdbd-mysql-perl, linux-nvidia, linux-nvidia-6.8, and tomcat9).

Linus has released 6.15-rc1 and closed the merge window for this release. "As expected, this was one of the bigger merge windows, almost certainly just because we had some pent-up development due to the previous releases being impacted by the holiday season. That said, while it's bigger than normal, it's not some kind of record-breaking thing.". In the end, 12.633 non-merge changesets were pulled into the mainline during this merge window.

A typical cloud-computing host will share some of its memory with each guest that it runs. The host retains its access to that memory, though, meaning that it can readily dig through that memory in search of data that the guest would prefer to keep private. The guest_memfd subsystem removes (most of) the host's access to guest memory, making the guest's data more secure. In the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, David Hildenbrand ran a discussion on the state and future of this feature.

Alistair Popple started his session at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit by proclaiming that ZONE_DEVICE is "the ugly stepchild" of the kernel's memory-management subsystem. Ugly or not, the ability to manage memory that is attached to a peripheral device rather than a CPU is increasingly important on current hardware. Popple hoped to cover some of the challenges with ZONE_DEVICE and find ways to make the stepchild a bit more attractive, if not bring it into the family entirely.

At last year's Linux Storage, Filesystem, Memory-Management, and BPF Summit (LSFMM+BPF), there was a discussion about atomic writes that was accompanied by patches to support the feature in the block layer, and for direct I/O on XFS. That work was merged, but another piece of that discussion concerned adding the feature for buffered I/O, in part because the PostgreSQL database currently has to jump through hoops to ensure that its writes are not "torn" (partially written) when there is an error or crash. Luis Chamberlain led a combined storage and filesystem track at this year's summit to revisit the idea of providing atomic (or untorn) writes for buffered I/O.

Yonghong Song brought a story about tracking down the cause of a strange verifier error message to the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit. He then presented some possible ways to improve Clang's user experience for anyone running into the same class of error in the future. Toward the end of his allotted time, he also discussed the problems with optimizations that change the signature of functions — a problem that José Marchesi had also brought up in the previous session.

Security updates have been issued by AlmaLinux (firefox), Debian (atop and thunderbird), Fedora (webkitgtk), Mageia (microcode), Oracle (expat), SUSE (apparmor, assimp-devel, aws-efs-utils, expat, firefox, ghostscript, go1.23, gotosocial, govulncheck-vulndb, GraphicsMagick, headscale, libmozjs-128-0, libsaml-devel, openvpn, perl-Data-Entropy, and xz), and Ubuntu (gnupg2, kernel, linux-azure-fips, linux-iot, openvpn, ruby-saml, and xz-utils).

Address-space isolation may well be, as Brendan Jackman said at the beginning of his memory-management-track session at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, "some security bullshit". But it also holds the potential to protect the kernel from a wide range of vulnerabilities, both known and unknown, while reducing the impact of existing mitigations. Implementing address-space isolation with reasonable performance, though, is going to require some significant changes. Jackman was there to get feedback from the memory-management community on how those changes should be implemented.

The kernel must often step through the page tables of one or more processes to carry out various operations. This "page-table walking" tends to be performed by ad-hoc (duplicated) code all over the kernel. Oscar Salvador used a memory-management-track session at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit to talk about strategies to unify the kernel's page-table walking code just a little bit by making hugetlb pages look more like ordinary pages.

Version 1.86.0 of the Rust language has been released. Changes include support for trait upcasting, the ability to index multiple elements of HashMaps and slices mutably, and a number of stabilized APIs.

Security updates have been issued by AlmaLinux (expat), Debian (chromium, commons-vfs, firefox-esr, php-horde-editor, php-horde-imp, and thunderbird), Fedora (corosync, firefox, nextcloud, and suricata), Mageia (curl and upx), Oracle (emacs, fence-agents, freetype, kernel, libreoffice, libxml2, nginx:1.24, podman, python-jinja2, and tigervnc), Red Hat (firefox and python-jinja2), SUSE (assimp, ffmpeg-4, firefox, ghostscript, GraphicsMagick, libxslt, and tomcat), and Ubuntu (linux, linux-aws, linux-aws-5.15, linux-gcp, linux-gke, linux-gkeop, linux-ibm, linux-intel-iotg, linux-kvm, linux-lowlatency, linux-lowlatency-hwe-5.15, linux-meta-raspi, linux-nvidia-tegra, linux-oracle, linux-oracle-5.15, linux-raspi, linux, linux-azure, linux-azure-5.4, linux-bluefield, linux-gcp, linux-ibm, linux-kvm, linux-oracle, linux-oracle-5.4, linux-xilinx-zynqmp, linux-fips, linux-fips, linux-aws-fips, linux-gcp-fips, linux-hwe-5.15, and linux-realtime, linux-intel-iot-realtime).

Inside this week's LWN.net Weekly Edition:

• Front: Calibre 8.0; Fedora reproducibility; OpenWrt One; 6.15 Merge Window; LSFMM+BPF coverage including BPF in GCC, Rust merging process, and more.
• Briefs: Ubuntu namespaces; New FPL; PorteuX 2.0; Firefox 137.0; GCC Rust; Rockbox 4.0; Rust specification; Thundermail; Dave Täht RIP; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

Saying that calibre is ebook-management software undersells the application by a fair margin. Calibre is an open-source Swiss Army knife for ebooks that can be used for everything from creating ebooks, converting ebooks from obscure formats to modern formats like EPUB, to serving up an ebook library over the web. The most recent major release, calibre 8.0, brings a better text-to-speech engine, a tool for creating audio overlays when authoring ebooks, support for profiles in the ebook viewer, and more.

José Marchesi and David Faust kicked off the BPF track at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit with an extra-long session on what they have been doing to support compiling to BPF in GCC. Overall, the project is slowly working toward full support for BPF, with most of the self-tests now passing using Faust's in-progress patches. However, the progress toward that goal has turned up a number of problems with how Clang supports BPF that needed to be discussed at length to find a path forward for both projects.