Linux Weekly News

On the second day of the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM), Goldwyn Rodrigues led a combined filesystem and memory-management session on saving memory when reading files that share extents. That kind of sharing can occur with copy-on-write (COW) filesystems, reflinks, snapshots, and other features of that sort. When reading those files, memory is wasted because multiple copies of the same data is stored in the page cache, so he wanted to explore adding a cache specifically to handle that.

This Google blog entry looks at some zero-day Android exploits that were detected and makes it clear what the stakes are.

We assess with high confidence that these exploits were packaged by a single commercial surveillance company, Cytrox, and sold to different government-backed actors who used them in at least the three campaigns discussed below. Consistent with findings from CitizenLab, we assess likely government-backed actors purchasing these exploits are operating (at least) in Egypt, Armenia, Greece, Madagascar, Côte d’Ivoire, Serbia, Spain and Indonesia.

In a fast-paced talk at PyCon 2022 in Salt Lake City, Utah, Pablo Galindo Salgado described some changes he and others have made to the error reporting for CPython 3.10. He painted a picture of a rather baffling set of syntax errors reported by earlier interpreter versions and how they have improved. This work is not done by any means, he said, and encouraged attendees to get involved in making error reporting even better in future Python versions.

Security updates have been issued by Debian (firefox-esr and openldap), Fedora (curl), Oracle (kernel and kernel-container), Red Hat (maven:3.5), SUSE (cacti, cacti-spine, firefox, go1.18, openldap2, python-requests, rsyslog, and slurm_20_11), and Ubuntu (firefox, htmldoc, libpng, libxfixes, libxrender, thunderbird, and vim).

Version 3.16.0 of the Alpine Linux distribution has been released. Significant changes include a switch to tmpfs for the /tmp directory, the splitting out of a number of NetworkManager plugins into separate packages, the removal of Python 2, and a lot of updated packages; see the release notes for more information.

The 5.18 kernel was released on May 22 after a nine-week development cycle. That can only mean that the time has come to look at some of the statistics behind this release, which was one of the busiest in a while. Read on for a look at the 5.18 kernel, where the code in this release came from, and how it found its way into the mainline.

Systemd 251 is out. The list of changes includes an increase of the minimum kernel version to 4.15, use of C11 to build the program, increased use of filesystem ID mapping, and many other things; see the announcement for all the details.

Security updates have been issued by Debian (admesh, condor, firefox-esr, libpgjava, libxml2, rsyslog, and thunderbird), Fedora (dotnet6.0, libarchive, php-openpsa-universalfeedcreator, thunderbird, and vim), Mageia (ffmpeg, kernel, kernel-linus, microcode, netatalk, nvidia-current, nvidia390, opencontainers-runc, postgresql, and ruby-nokogiri), Slackware (mariadb and mozilla), and SUSE (curl, firefox, libarchive, librecad, libxls, openldap2, php7, and postgresql10).

Linus has released the 5.18 kernel. "No unexpected nasty surprises this last week, so here we go with the 5.18 release right on schedule." Some of the headline changes in this release include the DAMOS memory-management interface, a number of random-number-generator improvements, the Intel software-defined silicon driver, strict memcpy() bounds checking, a switch to the C11 standard, and more. Also, the Reiserfs filesystem has been deprecated and the last vestiges of a.out support have been removed. See the LWN merge-window summaries (part 1, part 2) and the KernelNewbies 5.18 page for more details.

For readers who want to follow our article stream on Mastodon, LWN now (finally) has a presence in the Fosstodon community; you can find us at @LWN@fosstodon.org.

The final session in the memory-management track at the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM) was run remotely by James Gowans and David Woodhouse. It was titled "user-space control of memory mappings", with a subtitle of "letting guest memory and state survive kexec". Some options were discussed, but the real work is clearly yet to be done.

As the memory-management track at the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM) neared its conclusion, Mike Kravetz ran a session remotely to talk about page sharing with hugetlbfs, which is a special filesystem that provides access to huge pages. (See this article series for lots of information about hugetlbfs). Hugetlbfs can help to reduce page-table overhead when pages are shared between large numbers of processes, but there is a problem that he is trying to find a solution for.

The numerous correctness problems with the kernel's get_user_pages() functionality have been a fixture at the Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM) for some years. The 2022 event did not break that tradition. The first-day discussion on page pinning was covered here. On the final day, in the memory-management track, David Hildenbrand led a session on the current status of get_user_pages() and its interaction with copy-on-write (COW) memory.

Security updates have been issued by CentOS (kernel), Debian (ark, openldap, and thunderbird), Fedora (freetype and vim), Oracle (.NET 5.0, .NET 6.0, .NET Core 3.1, container-tools:3.0, glibc, kernel, rsync, and subversion:1.10), Scientific Linux (kernel), SUSE (dcraw, firefox, glib2, ImageMagick, kernel-firmware, libxml2, libyajl, php7, ucode-intel, and unrar), and Ubuntu (openldap).

Version 1.61.0 of the Rust language has been released. Changes this time around include more flexibility in main-program exit codes, a number of new features for const functions, a number of newly stabilized APIs, and more.

Control groups are a useful system-management feature, but they can also consume a lot of resources, especially if they hang around on the system after they have been deleted. Roman Gushchin described the problems that can result at the 2019 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM); he returned during the 2022 LSFMM to revisit the issue, especially as it relates to the memory controller. Progress has been made, but the problem is not yet solved.

During the final day of the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM), attention in the memory-management track turned once again to the challenges posed by the upcoming Compute Express Link (CXL) technology. Two sessions looked at different problems posed by CXL memory, which can come and go over the operation of the system. CXL offers a lot of flexibility, but changes will be needed for the kernel to be able to take advantage of it.

Andrew 'bunnie' Huang has posted an extensive review of the Rust language derived from the experience of writing "over 100k lines" of code.

Rust is a difficult language for authoring code because it makes these "cheats" hard – as long as you have the discipline of not using "unsafe" constructions to make cheats easy. However, really hard does not mean impossible – there were definitely some cheats that got swept under the rug during the construction of Xous.

This is where Rust really exceeded expectations for me. The language's structure and tooling was very good at hunting down these cheats and refactoring the code base, thus curing the cancer without killing the patient, so to speak. This is the point at which Rust’s very strict typing and borrow checker converts from a productivity liability into a productivity asset.

Security updates have been issued by Fedora (microcode_ctl, rubygem-nokogiri, and vim), Mageia (htmldoc, python-django, and python-oslo-utils), Red Hat (container-tools:2.0, kernel, kernel-rt, kpatch-patch, and pcs), SUSE (ardana-barbican, grafana, openstack-barbican, openstack-cinder, openstack-heat-gbp, openstack-horizon-plugin-gbp-ui, openstack-ironic, openstack-keystone, openstack-neutron-gbp, python-lxml, release-notes-suse-openstack-cloud, autotrace, curl, firefox, libslirp, php7, poppler, slurm_20_11, and ucode-intel), and Ubuntu (bind9, gnome-control-center, and libxrandr).

The LWN.net Weekly Edition for May 19, 2022 is available.