Linux Weekly News

One of the under-the-hood changes in the Fedora 33 release was a switch to systemd-resolved for the handling of DNS queries. This change should be invisible to most users unless they start using one of the new features provided by systemd-resolved. Recently, though, the Fedora project changed its default configuration for that service to eliminate fallback DNS servers — a change which is indeed visible to some users who have found themselves without domain-name resolution as a result.

Security updates have been issued by Arch Linux (ansible-base, keycloak, mumble, and postgresql), Debian (firefox-esr and nodejs), Fedora (dotnet3.1, dotnet5.0, keylime, php-horde-Horde-Text-Filter, radare2, scap-security-guide, and wireshark), openSUSE (postgresql, postgresql13 and python-djangorestframework), Red Hat (Ansible, firefox, and thunderbird), Scientific Linux (firefox and thunderbird), SUSE (php7, postgresql-jdbc, python-cryptography, rpmlint, and webkit2gtk3), and Ubuntu (dnsmasq, linux, linux-aws, linux-aws-5.4, linux-azure, linux-azure-5.4, linux-gcp, linux-gcp-5.4, 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-hwe, linux-azure, linux-azure-4.15, linux-dell300x, linux-gcp, linux-gcp-4.15, linux-gke-4.15, linux-hwe, linux-kvm, linux-oracle, linux-raspi2, linux-snapdragon, linux, linux-aws, linux-azure, linux-gcp, linux-hwe-5.8, linux-kvm, linux-oracle, linux-raspi, linux, linux-aws, linux-kvm, linux-lts-xenial, linux-raspi2, linux-snapdragon, linux-oem-5.10, linux-oem-5.6, screen, and xterm).

The LWN.net Weekly Edition for February 25, 2021 is available.

Two separate vulnerabilities led to the fast-tracked release of Python 3.9.2 and 3.8.8 on February 19, though source-only releases of 3.7.10 and 3.6.13 came a few days earlier. The vulnerabilities may be problematic for some Python users and workloads; one could potentially lead to remote code execution. The other is, arguably, not exactly a flaw in the Python standard library—it simply also follows an older standard—but it can lead to web cache poisoning attacks.

Sergio Durigan Junior has announced the availability of a debuginfod server for Debian systems. "In a nutshell, by using a debuginfod service you will not need to install debuginfo (a.k.a. dbgsym) files anymore; the symbols will be served to GDB (or any other debuginfo consumer that supports debuginfod) over the network. Ultimately, this makes the debugging experience much smoother (I myself never remember the full URL of our debuginfo repository when I need it)."

Security updates have been issued by openSUSE (firefox and tor), Oracle (stunnel and xterm), Red Hat (virt:8.2 and virt-devel:8.2 and xterm), SUSE (avahi, gnuplot, java-1_7_0-ibm, and pcp), and Ubuntu (openssl).

NumPy is a Python library that adds an array data type to the language, along with providing operators appropriate to working on arrays and matrices. By wrapping fast Fortran and C numerical routines, NumPy allows Python programmers to write performant code in what is normally a relatively slow language. NumPy 1.20.0 was announced on January 30, in what its developers describe as the largest release in the history of the project. That makes for a good opportunity to show a little bit about what NumPy is, how to use it, and to describe what's new in the release.

The 5.11.1, 5.10.18, 5.4.100, 4.19.177, 4.14.222, 4.9.258, and 4.4.258 stable kernels have all been released; each contains another set of important fixes.

The Firefox 86.0 release is out. New features this time include picture-in-picture video and "total cookie protection", which appears to be a way to allow third-party cookies while preserving some privacy.

Security updates have been issued by Arch Linux (connman, firejail, kernel, python-django, roundcubemail, and wpa_supplicant), Fedora (gdk-pixbuf2 and gdk-pixbuf2-xlib), openSUSE (python3 and tomcat), Scientific Linux (xterm), SUSE (postgresql12 and postgresql13), and Ubuntu (gdk-pixbuf, openldap, python-django, and qemu).

The beginning of the 5.12 merge window was delayed as the result of severe weather in the US Pacific Northwest. Once Linus Torvalds got going, though, he wasted little time; as of this writing, just over 8,600 non-merge changesets have been pulled into the mainline repository for the 5.12 release — over a period of about two days. As one might imagine, that work contains a long list of significant changes.

Matthew Garrett recently posted a patch set enabling hibernation on systems that are running in the UEFI secure-boot lockdown mode. This blog entry gets into the details of how it all works. "When we encrypt material with the TPM, we can ask it to record the PCR state. This is given back to us as metadata accompanying the encrypted secret. Along with the metadata is an additional signature created by the TPM, which can be used to prove that the metadata is both legitimate and associated with this specific encrypted data. In our case, that means we know what the value of PCR 23 was when we encrypted the key. That means that if we simply extend PCR 23 with a known value in-kernel before encrypting our key, we can look at the value of PCR 23 in the metadata. If it matches, the key was encrypted by the kernel - userland can create its own key, but it has no way to extend PCR 23 to the appropriate value first. We now know that the key was generated by the kernel."

Version 19 of the Kodi "entertainment center" application is out with a long list of new features.

For audio and music lovers, there are significant improvements across the board to metadata handling: library improvements, new tags, new displays, improvements to how Kodi handles release dates, album durations, multi-disc sets, and more. There's a new, Matrix-inspired visualisation, there are improvements to display when fetching files from a web server, and several changes to how audio decoder addons can pass information through to the Kodi player.

For video, most of the changes are more technical, and may depend on your hardware: AV1 software decoding, HLG HDR and static HDR10 playback on Windows 10, static HDR10 and dynamic Dolby Vision HDR support on Android, and more OpenGL bicubic scalers.

Security updates have been issued by Debian (chromium, libzstd, openldap, openvswitch, screen, and wpa), Fedora (dotnet5.0, subversion, and wpa_supplicant), openSUSE (mumble, python-djangorestframework, and tor), Oracle (container-tools:ol8, kernel, nodejs:10, nodejs:12, nodejs:14, subversion:1.10, and xterm), Red Hat (stunnel and xterm), and SUSE (ImageMagick, java-1_8_0-openjdk, kernel, krb5-appl, python3, tomcat, and webkit2gtk3).

Lockless algorithms are of interest for the Linux kernel when traditional locking primitives either cannot be used or are not performant enough. For this reason they come up every now and then on LWN; one of the last mentions, which prompted me to write this article series, was last July. Topics that arise even more frequently are read-copy-update (RCU — these articles from 2007 are still highly relevant), reference counting, and ways of wrapping lockless primitives into higher-level, more easily understood APIs. These articles will delve into the concepts behind lockless algorithms and how they are used in the kernel.

Security updates have been issued by Debian (bind9, libbsd, openssl1.0, php-horde-text-filter, qemu, and unrar-free), Fedora (kiwix-desktop and libntlm), Mageia (coturn, mediawiki, privoxy, and veracrypt), openSUSE (buildah, libcontainers-common, podman), Oracle (kernel, nss, and perl), Red Hat (xterm), SUSE (java-1_7_1-ibm, php74, python-urllib3, and qemu), and Ubuntu (libjackson-json-java and shiro).

The copy_file_range() system call looks like a relatively straightforward feature; it allows user space to ask the kernel to copy a range of data from one file to another, hopefully applying some optimizations along the way. In truth, this call has never been as generic as it seems, though some changes made during 5.3 helped in that regard. When the developers of the Go language ran into problems with copy_file_range(), there ensued a lengthy discussion on how this system call should work and whether the kernel needs to do more to make it useful.

Security updates have been issued by Debian (mumble, openssl, php7.3, and webkit2gtk), openSUSE (jasper, php7, and screen), SUSE (bind, php7, and php72), and Ubuntu (bind9, openssl, openssl1.0, and webkit2gtk).

The Google Security Blog carries an announcement of a heightened effort to reimplement security-critical software in memory-safe languages. "The new Rust-based HTTP and TLS backends for curl and now this new TLS library for Apache httpd are an important starting point in this overall effort. These codebases sit at the gateway to the internet and their security is critical in the protection of data for millions of users worldwide."

The LWN.net Weekly Edition for February 18, 2021 is available.