Linux, famously, appears in a wide range of systems. While servers and large data centers get a lot of the attention, and this year will always be the year of the Linux desktop, there is also a great deal of Linux to be found in realtime and embedded applications. Two talks held in the realtime and embedded tracks of the 2024 Open Source Summit North America provided listeners with an update on how Linux is doing in those areas. Work on realtime Linux appears to be nearing completion, while the embedded community is still pushing forward at full speed.

The LWN.net Weekly Edition for April 25, 2024 is available.

Version 9.0 of the QEMU emulator has been released. "This release contains 2700+ commits from 220 authors." The list of improvements is long; see the announcement and the changelog for details.

The Rust programming language, it is hoped, will bring a new level of safety to the Linux kernel. At the moment, though, there are still a number of impediments to getting useful Rust code into the kernel. In the Embedded Open Source Summit track of the Open Source Summit North America, Fabien Parent provided an overview of his work aimed at improving the infrastructure needed to write the device drivers needed by embedded systems in Rust; there is still some work to be done.

Security updates have been issued by Debian (glibc and samba), Fedora (chromium, cjson, mingw-python-idna, and pgadmin4), Mageia (kernel, kmod-xtables-addons, kmod-virtualbox, kernel-linus, and perl-Clipboard), Red Hat (go-toolset:rhel8, golang, java-11-openjdk, kpatch-patch, and shim), Slackware (freerdp), SUSE (apache-commons-configuration, glibc, jasper, polkit, and qemu), and Ubuntu (google-guest-agent, google-osconfig-agent, linux-lowlatency-hwe-6.5, pillow, and squid).

The Open Home Foundation has announced its existence as a home and support resource for free home-automation projects.

We created the Open Home Foundation to fight for the fundamental principles of privacy, choice, and sustainability for smart homes. And every person who lives in one.

Ahead of today, we've transferred over 240 projects, standards, drivers, and libraries—Home Assistant, ESPHome, Zigpy, Piper, Improv Wi-Fi, Wyoming, and so many more—to the Open Home Foundation. This is all about looking into the future. We've done this to create a bulwark against surveillance capitalism, the risk of buyout, and open-source projects becoming abandonware. To an extent, this protection extends even against our future selves—so that smart home users can continue to benefit for years, if not decades. No matter what comes.

Peter Hutterer announces udev-hid-bpf, a tool to facilitate the loading of BPF programs that make human-input devices work correctly.

eBPF was originally written for network packet filters but as of kernel v6.3 and thanks to Benjamin, we have BPF in the HID subsystem. HID actually lends itself really well to BPF because, well, we have a byte array and to fix our devices we need to do complicated things like "toggle that bit to zero" or "swap those two values".

See this article for more information on the BPF-HID mechanism.

Linus has released 6.9-rc5 for testing.

But if you ignore those oddities, it all looks pretty normal and things appear fairly calm. Which is just as well, since the first part of the week I was on a quick trip to Seattle, and the second part of the week I've been doing a passable imitation of the Fontana di Trevi, except my medium is mucus.

Kernel developers, like conscientious developers for many projects, will often include checks in the code for conditions that are never expected to occur, but which would indicate a serious problem should that expectation turn out to be incorrect. For years, developers have been encouraged (to put it politely) to avoid using assertions that crash the machine for such conditions unless there is truly no alternative. Increasingly, though, use of the kernel's WARN_ON() family of macros, which developers were told to use instead, is also being discouraged.

Version 0.81 of the PuTTY SSH client is out with a fix for CVE-2024-31497; some users will want to update and generate new keys:

PuTTY 0.81, released today, fixes a critical vulnerability CVE-2024-31497 in the use of 521-bit ECDSA keys (ecdsa-sha2-nistp521). If you have used a 521-bit ECDSA private key with any previous version of PuTTY, consider the private key compromised: remove the public key from authorized_keys files, and generate a new key pair.

However, this only affects that one algorithm and key size. No other size of ECDSA key is affected, and no other key type is affected.

(Thanks to Joe Nahmias).

Security updates have been issued by Debian (php7.4 and php8.2), Fedora (c-ares), Mageia (python-pillow and upx), Oracle (bind and dhcp, bind9.16, httpd:2.4/mod_http2, kernel, rear, and unbound), SUSE (eclipse, maven-surefire, tycho, emacs, kubevirt, virt-api-container, virt-controller-container, virt-exportproxy-container, virt-exportserver-container, virt-handler-container, virt-launcher-container, virt-libguestfs-t, nodejs16, nodejs18, nodejs20, texlive, vim, webkit2gtk3, and xen), and Ubuntu (gnutls28, klibc, libvirt, nodejs, and webkit2gtk).

The Open Source Security Foundation and the OpenJS Foundation have jointly posted a warning about XZ-like social-engineering attacks after OpenJS was seemingly targeted.

The OpenJS Foundation Cross Project Council received a suspicious series of emails with similar messages, bearing different names and overlapping GitHub-associated emails. These emails implored OpenJS to take action to update one of its popular JavaScript projects to "address any critical vulnerabilities," yet cited no specifics. The email author(s) wanted OpenJS to designate them as a new maintainer of the project despite having little prior involvement.

The 6.9-rc4 kernel prepatch is out for testing. "Nothing particularly unusual going on this week - some new hw mitigations may stand out, but after a decade of this I can't really call it 'unusual' any more, can I?"

The 6.8.6, 6.6.27, 6.1.86, 5.15.155, 5.10.215, 5.4.274, and 4.19.312 stable kernel updates have all been released; each contains a relatively large number of important fixes.

The kernel project merges dozens of drivers with every development cycle, and almost every one of those drivers is entirely uncontroversial. Occasionally, though, a driver submission raises wider questions, leading to lengthy discussion and, perhaps, opposition. That is currently the case with two separate drivers, both with ties to the networking subsystem. One of them is hung up on questions of whether (and how) all device functionality should be made available to user space, while the other has run into turbulence because it drives a device that is unobtainable outside of a single company.

Dirk Mueller has posted a lengthy analysis of the XZ backdoor on the openSUSE News site, with a focus on openSUSE's response.

Debian, as well as the other affected distributions like openSUSE are carrying a significant amount of downstream-only patches to essential open-source projects, like in this case OpenSSH. With hindsight, that should be another Heartbleed-level learning for the work of the distributions. These patches built the essential steps to embed the backdoor, and do not have the scrutiny that they likely would have received by the respective upstream maintainers. Whether you trust Linus Law or not, it was not even given a chance to chime in here. Upstream did not fail on the users, distributions failed on upstream and their users here.

The Earliest Virtual Deadline First (EEVDF) scheduler was merged as an option for the 6.6 kernel. It represents a major change to how CPU scheduling is done on Linux systems, but the EEVDF front has been relatively quiet since then. Now, though, scheduler developer Peter Zijlstra has returned from a long absence to post a patch series intended to finish the EEVDF work. Beyond some fixes, this work includes a significant behavioral change and a new feature intended to help latency-sensitive tasks.

Security updates have been issued by AlmaLinux (kernel, less, libreoffice, nodejs:18, nodejs:20, rear, thunderbird, and varnish), Debian (pillow), Fedora (dotnet7.0), SUSE (sngrep, texlive-specs-k, tomcat, tomcat10, and xorg-x11-server), and Ubuntu (nss, squid, and util-linux).

The mainline kernel has just received a set of commits mitigating the latest x86 hardware vulnerability, known as "branch history injection". From this commit:

Branch History Injection (BHI) attacks may allow a malicious application to influence indirect branch prediction in kernel by poisoning the branch history. eIBRS isolates indirect branch targets in ring0. The BHB can still influence the choice of indirect branch predictor entry, and although branch predictor entries are isolated between modes when eIBRS is enabled, the BHB itself is not isolated between modes.

See this commit for documentation on the command-line parameter that controls this mitigation. There are stable kernel releases (6.8.5, 6.6.26, 6.1.85, and 5.15.154) in the works that also contain the mitigations.