Linus has released 6.18-rc7, probably the last -rc before the 6.18 release.

So the rc6 kernel wasn't great: we had a last-minute core VM regression that caused people problems.

That's not a great thing late in the release cycle like that, but it was a fairly trivial fix, and the cause wasn't some horrid bug, just a latent gotcha that happened to then bite a late VM fix. So while not great, it also doesn't make me worry about the state of 6.18. We're still on track for a final release next weekend unless some big new problem rears its ugly head.

The Oracle blog has a lengthy article on enhancements to GCC to help detect overflows of flexible array members (FAMs) in C programs.

We describe here two new GNU extensions which specify size information for FAMs. These are a new attribute, "counted_by" and a new builtin function, "__builtin_counted_by_ref". Both extensions can be used in GNU C applications to specify size information for FAMs, improving the buffer overflow detection for FAMs in general.

This work has been covered on LWN as well.

The call for candidates for the 2025 election for the Linux Foundation Technical Advisory Board has been posted.

The TAB exists to provide advice from the kernel community to the Linux Foundation and holds a seat on the LF's board of directors; it also serves to facilitate interactions both within the community and with outside entities. Over the last year, the TAB has overseen the organization of the Linux Plumbers Conference, advised on the setup of the kernel CVE numbering authority, worked behind the scenes to help resolve a number of contentious community discussions, worked with the Linux Foundation on community conference planning, and more.

Nominations close on December 13.

Version 8.5.0 of the PHP language has been released. Changes include a new "|>" operator that, for some reason, makes these two lines equivalent:

    $result = strlen("Hello world");
    $result = "Hello world" |> strlen(...);

Other changes include a new function attribute, "#[\NoDiscard]" to indicate that the return value should be used, attributes on constants, and more; see the migration guide for details.

BPF allows programs uploaded from user space to be run, safely, within the kernel. The io_uring subsystem, too, can be thought of as a way of loading programs in the kernel, though the programs in question are mostly a sequence of I/O-related system calls. It has sometimes seemed inevitable that io_uring would, like many other parts of the kernel, gain BPF capabilities as a way of providing more flexibility to user space. That has not yet happened, but there are currently two patch sets under consideration that take different approaches to the problem.

Inside this week's LWN.net Weekly Edition:

• Front: Hardware architectures; Fedora Flatpaks; Debian hardware support; sockaddr structure; NUMA nodes; Homebrew.
• Briefs: LightDM security; Debian Libre Live; Xubuntu postmortem; Blender 5.0; Git 2.52.0; Rust in Android; Thunderbird 145; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

Version 2.52.0 of the Git source-code management system has been released. Changes include a new last-modified command to find the closest ancestor commit that touched one or more paths, a couple of git refs improvements, a new git repo command for obtaining information about the repository itself, and more. See the announcement and this GitHub blog entry for more information.

For better or for worse, the NUMA node is the abstraction used by the kernel to keep track of different types of memory. How that abstraction is used, though, is still an active area of development. Two patch sets focused on this problem are currently under review; one addresses the perennial problem of promoting heavily used folios from slower to faster memory, while the other aims to improve the kernel's handling of nodes containing special memory installed for a specific purpose.

Linus has released 6.18-rc6 for testing. "So we have a slightly larger rc6 than usual, but I think it's just the random noise and a result of pull request timings rather than due to any issues with the release. But I guess we have a couple of weeks remaining to find out."

One of the many objectives of the Linux Kernel Self-Protection Project (KSPP), which just completed ten years of work, is to ensure that all array references can be bounds-checked, even in the case of flexible array members, the size of which is not known at compile time. One of the most challenging flexible array members in the kernel is not even declared as such. Almost exactly one year ago, LWN looked at the effort to increase safety around the networking subsystem's heavily used sockaddr structure. One year later, Kees Cook is still looking for a way to bring this work to a close.

The Google Security Blog has a new post on just how well the use of Rust is working out for the Android project.

We adopted Rust for its security and are seeing a 1000x reduction in memory safety vulnerability density compared to Android's C and C++ code. But the biggest surprise was Rust's impact on software delivery. With Rust changes having a 4x lower rollback rate and spending 25% less time in code review, the safer path is now also the faster one.

Longtime LWN readers will have encountered the concept of "stable pages" before; it was first covered here nearly 15 years ago. For the most part, the problem that stable pages were meant to solve — preventing errors when user space modifies a buffer that is under I/O — has been dealt with. But recent discussions show that there is one area where problems remain: direct I/O. There is some disagreement, though, over whether those problems are the result of user-space bugs and how much of a performance price should be paid to address them.

Version 2.0.0 of public-inbox, the mail archiving system behind lore.kernel.org and LWN's email archive, has been released. "This release includes several new features and fixes; mostly around improved integration between inboxes and coderepos for solver. Portability and reliability is also improved, especially in the internal process management of lei."

The 6.18-rc5 kernel prepatch is out for testing. "In other words: it all looks just the way I like it at this point: small and boring."

The kernel community is currently reviewing a proposed policy for contributors who are using large language models to assist in the creation of their patches; the primary focus is on disclosure of the use of those tools. "The goal here is to clarify community expectations around tools. This lets everyone become more productive while also maintaining high degrees of trust between submitters and reviewers."

The future of the Filesystem Hierarchy Standard (FHS) has been under discussion for some time; now, Neal Gompa has announced that the FHS is "hosted and stewarded" by Freedesktop.org.

For those who are unaware, the Filesystem Hierarchy Standard (FHS) is the definition for POSIX operating systems to organize system and user data. It is broadly adopted by Linux, BSD, and other operating systems that follow POSIX-like conventions.

See this page for the specification's new home.

Filesystems are complex and performance-sensitive beasts. They can also present security concerns. Microkernel-based systems have long pushed filesystems into separate processes in order to contain any vulnerabilities that may be found there. Linux can do the same with the Filesystem in Userspace (FUSE) subsystem, but using FUSE brings a significant performance penalty. Darrick Wong is working on ways to eliminate that penalty, and he has a massive patch set showing how ext4 filesystems can be safely implemented in user space by unprivileged processes with good performance. This work has the potential to radically change how filesystems are managed on Linux systems.

Inside this week's LWN.net Weekly Edition:

• Front: Python thread safety; Namespace reference counting; Merigraf; Speeding up short reads; Julia 1.12; systemd security.
• Briefs: CHERIoT 1.0; Chromium XSLT; Arm KASLR; Bazzite; Devuan 6.0; Incus 6.18; LXQt 2.3.0; Rust 1.91.0; Quotes; ...
• Announcements: Newsletters, conferences, security updates, patches, and more.

The Project Zero blog explains that, on 64-bit Arm systems, the kernel's direct map is always placed at the same virtual location, regardless of whether kernel address-space layout randomization (KASLR) is enabled.

While it remains true that KASLR should not be trusted to prevent exploitation, particularly in local contexts, it is regrettable that the attitude around Linux KASLR is so fatalistic that putting in the engineering effort to preserve its remaining integrity is not considered to be worthwhile. The joint effect of these two issues dramatically simplified what might otherwise have been a more complicated and likely less reliable exploit.

Version 6.0 ("Excalibur") of the systemd-averse Devuan distribution has been released. It is based on Debian 13 ("trixie"), and includes some of the significant changes from that release, including the merged /usr hierarchy. See the release notes for details.