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The 5.13.5, 5.10.53, and 5.4.135 stable kernels have been released; each contains another set of important fixes.

After a long pause, the K-9 Android mail client project has released version 5.800. "The user interface has been redesigned. Some of you will love it, some will hate it. You’re welcome and sorry." There are also a number of improvements to make background operation work better on current Android systems.

The DAMON patch set was first covered here in early 2020; this work, now in its 34th revision, enables the efficient collection of information about memory-usage patterns on Linux systems. That data can then be used to influence the kernel's memory-management subsystem; one possible way to do that is to more aggressively reclaim memory that is not being used. To that end, DAMON author SeongJae Park is proposing a DAMON-based mechanism to perform user-controllable proactive reclaim.

Security updates have been issued by Arch Linux (chromium, curl, impacket, jdk11-openjdk, jre-openjdk, jre-openjdk-headless, jre11-openjdk-headless, kernel, lib32-curl, lib32-libcurl-compat, lib32-libcurl-gnutls, libcurl-compat, libcurl-gnutls, libpano13, linux-hardened, linux-lts, linux-zen, nvidia-utils, opera, systemd, and virtualbox), CentOS (java-11-openjdk and kernel), Debian (lemonldap-ng), Fedora (curl and podman), Gentoo (icedtea-web and velocity), openSUSE (bluez, go1.15, go1.16, kernel, thunderbird, transfig, and wireshark), Oracle (java-1.8.0-openjdk, java-11-openjdk, kernel, and kernel-container), SUSE (bluez, curl, kernel, qemu, thunderbird, transfig, and wireshark), and Ubuntu (curl).

Disagreements over which patches should find their way into stable updates are not new — or uncommon. So when the topic came up again recently, there was little reason to expect anything but more of the same. And, for the most part, that is what ensued but, in this exchange, we were also able to see the core issue that drives these discussions. There are, in the end, two fundamentally different views of what the stable tree should be.

Security updates have been issued by Debian (pillow and redis), Fedora (kernel-headers, kernel-tools, kernelshark, libbpf, libtraceevent, libtracefs, nextcloud, and trace-cmd), Gentoo (chromium and singularity), Mageia (kernel, kernel-linus, and systemd), openSUSE (caribou, chromium, curl, and qemu), Oracle (java-1.8.0-openjdk, java-11-openjdk, kernel, and systemd), Slackware (curl), SUSE (curl, kernel, linuxptp, python-pip, and qemu), and Ubuntu (ruby2.3, ruby2.5, ruby2.7).

The LWN.net Weekly Edition for July 22, 2021 is available.

A local root hole in the Linux kernel, called Sequoia, was disclosed by Qualys on July 20. A full system compromise is possible until the kernel is patched (or mitigations that may not be fully effective are applied). At its core, the vulnerability relies on a path through the kernel where 64-bit size_t values are "converted" to signed integers, which effectively results in an overflow. The flaw was reported to Red Hat on June 9, along with a local systemd denial-of-service vulnerability, leading to a kernel crash, found at the same time. Systems with untrusted local users need updates for both problems applied as soon as they are available—out of an abundance of caution, other systems likely should be updated as well.

Security updates have been issued by Arch Linux (ant, code, dino, firefox-ublock-origin, go, libuv, nextcloud-app-mail, nodejs-lts-erbium, nodejs-lts-fermium, openvswitch, putty, racket, telegram-desktop, and wireshark-cli), Debian (kernel, linux-4.19, and systemd), Fedora (kernel, kernel-headers, kernel-tools, and krb5), Gentoo (systemd), Mageia (perl-Convert-ASN1 and wireshark), openSUSE (caribou, containerd, crmsh, fossil, icinga2, kernel, nextcloud, and systemd), Red Hat (389-ds:1.4, glibc, java-1.8.0-openjdk, java-11-openjdk, kernel, kernel-rt, kpatch-patch, libldb, perl, RHV-H, rpm, shim and fwupd, and systemd), Slackware (kernel), SUSE (caribou, containerd, crmsh, curl, dbus-1, kernel, qemu, and systemd), and Ubuntu (binutils, linux, linux-aws, linux-aws-5.4, linux-azure, linux-azure-5.4, linux-gcp, linux-gcp-5.4, linux-gke, linux-gke-5.4, linux-gkeop, linux-gkeop-5.4, linux-hwe-5.4, linux-kvm, linux-oracle, linux-oracle-5.4, linux-raspi, linux-raspi-5.4, linux, linux-aws, linux-aws-5.8, linux-azure, linux-azure-5.8, linux-gcp, linux-gcp-5.8, linux-hwe-5.8, linux-kvm, linux-oracle, linux-oracle-5.8, linux-raspi, 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-raspi2, linux-snapdragon, linux, linux-aws, linux-azure, linux-gcp, linux-gke-5.3, linux-hwe, linux-lts-xenial, linux-kvm, linux-oracle, linux-raspi, linux-raspi2-5.3, linux-oem-5.10, nvidia-graphics-drivers-390, nvidia-graphics-drivers-418-server, nvidia-graphics-drivers-450-server, nvidia-graphics-drivers-460, nvidia-graphics-drivers-460-server, nvidia-graphics-drivers-470, and systemd).

Alyssa Rosenzweig goes into the details of the reverse-engineering of the Mali "Valhall" GPU instruction set.

Valhall linearizes Bifrost, removing the Very Long Instruction Word mechanisms of its predecessors. Valhall replaces the compiler’s static scheduling with hardware dynamic scheduling, trading additional control hardware for higher average performance. That means padding with “no operation” instructions is no longer required, which may decrease code size, promising better instruction cache use.

A document describing the instruction set has been released, along with an assembler and disassembler.

There is a lot of buzz around the Rust programming language these days—which strikes some folks as irritating, ridiculous, or both. But the idea of a low-level language that can replace C, with fewer built-in security pitfalls, is attractive for any number of projects. Recently, the Tor Project announced the Arti project as a complete Rust rewrite of Tor's core protocols, which provide internet privacy and anonymity. In addition, Tor announced that Arti received a grant to support its development over the next year or so.

The Stockfish project, which distributes a chess engine under GPLv3, has announced the filing of a GPL-enforcement lawsuit against ChessBase, which has been (and evidently still is) distributing proprietary versions of the Stockfish code.

In the past four months, we, supported by a certified copyright and media law attorney in Germany, went through a long process to enforce our license. Even though we had our first successes, leading to a recall of the Fat Fritz 2 DVD and the termination of the sales of Houdini 6, we were unable to finalize our dispute out of court. Due to Chessbase’s repeated license violations, leading developers of Stockfish have terminated their GPL license with ChessBase permanently. However, ChessBase is ignoring the fact that they no longer have the right to distribute Stockfish, modified or unmodified, as part of their products.

The 5.13.4, 5.12.19, 5.10.52, 5.4.134, 4.19.198, 4.14.240, 4.9.276, and 4.4.276 stable updates have all been released. These are relatively large updates once again, and they include the fix for the just-disclosed local root vulnerability. Note that the 5.12.x series ends with the 5.12.19 release.

Security updates have been issued by Debian (kernel, libjdom1-java, rabbitmq-server, and systemd), Fedora (glibc), Gentoo (libpano13, libslirp, mpv, pjproject, pycharm-community, and rpm), Mageia (glibc, libuv, mbedtls, rvxt-unicode, mxrvt, eterm, tomcat, and zziplib), openSUSE (dbus-1, firefox, go1.15, lasso, nodejs10, nodejs12, nodejs14, and sqlite3), SUSE (go1.15), and Ubuntu (containerd).

Commit 8cae8cd89f05 went into the mainline kernel repository on July 19; it puts a limit on the size of buffers allocated in the seq_file mechanism and mentions "int overflow pitfalls". For more information, look to this Qualys advisory describing the vulnerability:

We discovered a size_t-to-int conversion vulnerability in the Linux kernel's filesystem layer: by creating, mounting, and deleting a deep directory structure whose total path length exceeds 1GB, an unprivileged local attacker can write the 10-byte string "//deleted" to an offset of exactly -2GB-10B below the beginning of a vmalloc()ated kernel buffer.

It may not sound like much, but they claim to have written exploits for a number of Ubuntu, Debian, and Fedora distributions. Updates from distributors are already flowing, and this patch has been fast-tracked into today's stable kernel updates as well.

The lowly file descriptor is one of the fundamental objects in Linux systems. A file descriptor, which is a simple integer value, can refer to an open file — or to a network connection, a running process, a loaded BPF program, or a namespace. Over the years, the use of file descriptors to refer to transient objects has grown to the point that it can be difficult to justify an API that uses anything else. Interestingly, though, the io_uring subsystem looks as if it is moving toward its own number space separate from file descriptors.

As an example of what a "real" device driver in Rust would look like, Wedson Almeida Filho has posted a translation of the PL061 GPIO driver alongside the original. For ease of reading, the resulting HTML has been reformatted a bit and placed below; viewing in a wide window is recommended.

Stable kernels 5.13.3, 5.12.18, 5.10.51, and 5.4.133 have been released. They all contain important fixes and users should upgrade.

Security updates have been issued by Arch Linux (chromium, firefox, mbedtls, nextcloud, python-pillow, ruby, ruby2.6, ruby2.7, systemd, thunderbird, varnish, and vivaldi), Debian (thunderbird), Fedora (chromium, firefox, and linux-firmware), Gentoo (apache, commons-fileupload, dovecot, and mediawiki), openSUSE (firefox, fossil, go1.16, and icinga2), Oracle (firefox, kernel, and kernel-container), Red Hat (nettle), and SUSE (firefox and go1.16).

The 5.14-rc2 kernel prepatch is out for testing. Linus says:

At least in pure number of commits, this is the biggest rc2 we've had during the 5.x cycle. Whether that is meaningful or not, who knows - it might be just random timing effects, or it might indicate that this release is not going to be one of those nice and calm ones. We'll just have to wait and see.

In total, 421 non-merge changesets were pulled into the mainline between -rc1 and -rc2.