The Linux kernel is generally seen as a poor fit for safety-critical systems; it was never designed to provide realtime response guarantees or to be certifiable for such uses. But the systems that can be used in such settings lack the features needed to support complex applications. This problem is often solved by deploying a mix of computers running different operating systems. But what if you want to support a mixture of tasks, some safety-critical and some not, on the same system? At a talk given at LinuxLab 2018, Claudio Scordino described an effort to support this type of mixed-criticality system.

Greg Kroah-Hartman has released stable kernels 4.19.9, 4.14.88, 4.9.145, 4.4.167, and 3.18.129. They all contain important fixes and users should upgrade.

Security updates have been issued by Debian (firefox-esr), Fedora (singularity), openSUSE (compat-openssl098, cups, firefox, mozilla-nss, and xen), and SUSE (cups, exiv2, ghostscript, and git).

The LWN.net Weekly Edition for December 13, 2018 is available.

In the RDMA microconference of the 2018 Linux Plumbers Conference (LPC), John Hubbard, Dan Williams, and Matthew Wilcox led a discussion on the problems surrounding get_user_pages() (and friends) and the interaction with DMA. It is not the first time the topic has come up, there was also a discussion about it at the Linux Storage, Filesystem, and Memory-Management Summit back in April. In a nutshell, the problem is that multiple parts of the kernel think they have responsibility for the same chunk of memory, but they do not coordinate their activities; as might be guessed, mayhem can sometimes ensue.

The x32 subarchitecture is a software variant of x86-64; it runs the processor in the 64-bit mode, but uses 32-bit pointers and arithmetic. The idea is to get the advantages of x86-64 without the extra memory usage that goes along with it. It seems, though, that x32 is not much appreciated; few distributions support it and the number of users appears to be small. So now Andy Lutomirski is proposing its eventual removal:

I propose that we make CONFIG_X86_X32 depend on BROKEN for a release or two and then remove all the code if no one complains. If anyone wants to re-add it, IMO they're welcome to do so, but they need to do it in a way that is maintainable.

If there are x32 users out there, now would be a good time for them to speak up.

Security updates have been issued by Arch Linux (chromium, firefox, lib32-openssl, lib32-openssl-1.0, openssl, openssl-1.0, texlive-bin, and wireshark-cli), Fedora (perl), openSUSE (pdns), Oracle (kernel), Red Hat (kernel), Slackware (mozilla), SUSE (kernel, postgresql10, qemu, and xen), and Ubuntu (firefox, freerdp, freerdp2, pixman, and poppler).

Git 2.20.0 is out. Changes include interdiff generation support in git format-patch, an improved ability to cope with corrupted patches in git am, a number of performance and usability improvements, and more.

The Mozilla Blog takes a look at the Contextual Feature Recommender (CFR) in Firefox 64. "Aimed at people who are looking to get more out of their online experience or ways to level up. CFR is a system that proactively recommends Firefox features and add-ons based on how you use the web. For example, if you open multiple tabs and repeatedly use these tabs, we may offer a feature called “Pinned Tabs” and explain how it works. Firefox curates the suggested features and notifies you. With today’s release, we will start to rollout with three recommended extensions which include: Facebook Container, Enhancer for YouTube and To Google Translate. This feature is available for US users in regular browsing mode only. They will not appear in Private Browsing mode. Also, Mozilla does NOT receive a copy of your browser history. The entire process happens locally in your copy of Firefox." The release notes contain more details about this release.

Git does not handle large files very well. While there is work underway to handle large repositories through the commit graph work, Git's internal design has remained surprisingly constant throughout its history, which means that storing large files into Git comes with a significant and, ultimately, prohibitive performance cost. Thankfully, other projects are helping Git address this challenge. This article compares how Git LFS and git-annex address this problem and should help readers pick the right solution for their needs.

Security updates have been issued by Debian (php7.0), Fedora (keepalived, kernel, kernel-headers, kernel-tools, mingw-uriparser, and uriparser), openSUSE (pdns-recursor), Oracle (kernel), SUSE (compat-openssl098, glibc, java-1_8_0-ibm, kernel, opensc, python, python-base, python-cryptography, python-pyOpenSSL, samba, and soundtouch), and Ubuntu (cups).

There are a lot of claims regarding the relative security of containers versus virtual machines (VMs), but there has been little in the way of actually trying to measure those differences. James Bottomley gave a talk in the refereed track of the 2018 Linux Plumbers Conference (LPC) that described work that targets filling in that gap. He and his colleagues have come up with a measure that, while not perfect, gives a starting point for further efforts.

Version 15 of the Nextcloud productivity and communications platform is out. New features include Mastodon integration, two-factor authentication, a number of user-interface improvements, and more.

For those who would like a deeper understanding of how the human interface device (HID) protocol works, Peter Hutterer has posted a detailed overview. "Originally HID was designed to work over USB. But just like Shrek the technology world is obsessed with layers so these days HID works over different transport layers. HID over USB is what your mouse uses, HID over i2c may be what your touchpad uses. HID works over Bluetooth and it's celebrity-diet version BLE. Somewhere, someone out there is very slowly moving a mouse pointer by sending HID over carrier pigeons just to prove a point. Because there's always that one guy."

Kernel bugs can have all kinds of unfortunate consequences, from inconvenient crashes to nasty security vulnerabilities. Some of the most feared bugs, though, are those that corrupt data in filesystems. The losses imposed on users can be severe, and the resulting problems may not be noticed for a long time, making recovery difficult. Filesystem developers, knowing that they will have to face their users in the real world, go to considerable effort to prevent this kind of bug from finding its way into a released kernel. A recent failure in that regard raises a number of interesting questions about how kernel development is done.

Security updates have been issued by Debian (chromium-browser and lxml), Fedora (cairo, hadoop, and polkit), Mageia (tomcat), openSUSE (apache2-mod_jk, Chromium, dom4j, ImageMagick, libgit2, messagelib, ncurses, openssl-1_0_0, otrs, pam, php5, php7, postgresql10, rubygem-activejob-5_1, tiff, and tomcat), Red Hat (chromium-browser and rh-git218-git), Slackware (php), SUSE (audiofile, cri-o and kubernetes packages, cups, ImageMagick, libwpd, SMS3.2, and systemd), and Ubuntu (lxml).

The 4.20-rc6 kernel prepatch is out for testing. "Most of it looks pretty small and normal. Would I have preferred for there to be less churn? Yes. But it's certainly smaller than rc5 was, so we're moving in the right direction, and we have at least one more rc to go."

The stable kernel process continues to churn out releases; 4.19.8, 4.14.87, and 4.9.144 are now available with another set of important fixes.

Filesystem developers tend toward a high level of conservatism when it comes to making changes; given the consequences of mistakes, this seems like a healthy survival trait. One might rightly be tempted to regard a recent disagreement over the backporting of filesystem-related fixes to the stable kernels as an example of this conservatism, but there is more to it. The kernel development process has matured in many ways over the years; perhaps this discussion hints at some of the changes that will be needed to continue that maturation in the future.

Security updates have been issued by Arch Linux (jupyter-notebook), CentOS (ghostscript), Debian (libphp-phpmailer and policykit-1), Fedora (bird), Gentoo (ede), Mageia (flash-player-plugin), openSUSE (dom4j, dpdk, glib2, nextcloud, postgresql94, and qemu), Oracle (kernel), SUSE (firefox, libarchive, libgit2, libreoffice, ncurses, openssl-1_0_0, squid, and tiff), and Ubuntu (ghostscript, openssl, openssl1.0, and wavpack).