Linux Weekly News

Linus has released the 5.4 kernel. "Not a lot happened this last week, which is just how I like it". Significant features in this release include the haltpoll CPU governor, the iocost (formerly io.weight) I/O controller, the EROFS filesystem, an implementation of the exFAT filesystem that may yet be superseded by a better version, the fs-verity file integrity mechanism, support for the BPF compile once, run everywhere mechanism, the dm-clone device mapper target, the virtiofs filesystem, kernel lockdown support (at last), kernel symbol namespaces, and a new random-number generator meant to solve the early-boot entropy problem. See the KernelNewbies 5.4 page for a lot more details.

When virtio was merged in Linux v2.6.24, its author, Rusty Russell, described the goal as being for "common drivers to be efficiently used across most virtual I/O mechanisms". Today, much progress has been made toward that goal, with virtio supported by multiple hypervisors and guest drivers shipped by many operating systems. But these applications of virtio are implemented in software, whereas Michael Tsirkin's "VirtIO without the Virt" talk at KVM Forum 2019 laid out how to implement virtio in hardware.

Security updates have been issued by Fedora (dpdk, mingw-djvulibre, mingw-hunspell, mingw-ilmbase, mingw-OpenEXR, php-symfony, php-symfony3, and rsyslog), openSUSE (chromium and squid), SUSE (aspell, cups, djvulibre, and dpdk), and Ubuntu (djvulibre).

Over on the Project Zero blog, Maddie Stone has a lengthy post about a zero-day exploit that was found and fixed in the Android Binder interprocess communication mechanism. The post details the search for the problem, which was apparently being used in the wild, its fix, and how it can be exploited. This is all part of an effort to "make zero-day hard"; one of the steps the project is taking is to disseminate more information on these bugs. "Complete detailed analysis of the 0-days from the point of view of bug hunters and exploit developers and share it back with the community. Transparency and collaboration are key. We want to share detailed root cause analysis to inform developers and defenders on how to prevent these types of bugs in the future and improve detection. We hope that by publishing details about the exploit and its methodology, this can inform threat intelligence and incident responders. Overall, we want to make information that’s often kept in silos accessible to all."

Fedora's Modularity initiative has been no stranger to controversy since its inception in 2016. Among other things, there were enough problems with the original design that Modularity went back to the drawing board in early 2018. Modularity has since been integrated with both the Fedora and Red Hat Enterprise Linux (RHEL) distributions, but the controversy continues, with some developers asking whether it's time for yet another redesign — or to abandon the idea altogether. Over the last month or so, several lengthy, detailed, and heated threads have explored this issue; read on for your editor's attempt to integrate what was said.

Greg Kroah-Hartman has announced the release of the 5.3.12, 4.19.85, and 4.14.155 stable kernels. As usual, they contain fixes throughout the kernel tree; users of those series should upgrade.

Security updates have been issued by Fedora (oniguruma and thunderbird-enigmail), openSUSE (chromium, ghostscript, and slurm), Oracle (kernel), Red Hat (kpatch-patch), Slackware (bind), SUSE (python-ecdsa), and Ubuntu (bind9 and mariadb).

The LWN.net Weekly Edition for November 21, 2019 is available.

The idea of stacking (or chaining) Linux security modules (LSMs) goes back 15 years (at least) at this point; progress has definitely been made along the way, especially in the last decade or so. It has been possible to stack "minor" LSMs with one major LSM (e.g. SELinux, Smack, or AppArmor) for some time, but mixing, say, SELinux and AppArmor in the same system has not been possible. Combining major security solutions may not seem like a truly important feature, but there is a use case where it is pretty clearly needed: containers. Longtime LSM stacker (and Smack maintainer) Casey Schaufler gave a presentation at the 2019 Linux Security Summit Europe to report on the status and plans for allowing arbitrary LSM stacking.