Linux Weekly News

By the time the last pull request was acted on and 5.13-rc1 was released, a total of 14,231 non-merge commits had found their way into the mainline. That makes the 5.13 merge window larger than the entire 5.12 development cycle (13,015 commits) and just short of all of 5.11 (14,340). In other words, 5.13 looks like one of the busier development cycles we have seen for a little while. About 6,400 of these commits came in after the first-half summary was written, and they include a number of significant new features.

Security updates have been issued by Debian (libxml2), Fedora (autotrace, babel, kernel, libopenmpt, libxml2, mingw-exiv2, mingw-OpenEXR, mingw-openexr, python-markdown2, and samba), openSUSE (alpine, avahi, libxml2, p7zip, redis, syncthing, and vlc), and Ubuntu (webkit2gtk).

The first 5.13 kernel prepatch is out for testing, and the merge window is closed for this development cycle. "This was - as expected - a fairly big merge window, but things seem to have proceeded fairly smoothly. Famous last words." In the end, 14,231 non-merge changesets were pulled into the mainline during the merge window — more than were seen during the entire 5.12 cycle.

The IEEE, whose Symposium on Security and Privacy conference had accepted the "hypocrite commits" paper for publication, has posted a statement [PDF] on the episode.

The paper was reviewed by four reviewers in the Fall S&P 2021 review cycle and received a very positive overall rating (2 Accept and 2 Weak Accept scores, putting it in the top 5% of submitted papers). The reviewers noted that the fact that a malicious actor can attempt to intentionally add a vulnerability to an open source project is not new, but also acknowledged that the authors provide several new insights by describing why this might be easier than expected, and why it might be difficult for maintainers to detect the problem. One of the PC members briefly mentioned a possible ethical concern in their review, but that comment was not significantly discussed any further at the time; we acknowledge that we missed it.

The statement concludes with some actions to be taken by IEEE to ensure that ethically questionable papers are not accepted again.

While it is sometimes possible to perform I/O by moving data through the CPU, the only way to get the required level of performance is usually for devices to move data directly to and from memory. Direct memory access (DMA) I/O has been well supported in the Linux kernel since the early days, but there are always ways in which that support can be improved, especially when hardware adds some challenges of its own. The somewhat confusingly named "non-contiguous" DMA API that was added for 5.13 shows the kinds of things that have to be done to get the best performance on current systems.

New stable kernels 5.12.2, 5.11.19, 5.10.35, 5.4.117, and 4.19.190 have been released. They contain a relatively short list of updates throughout the tree; users of those series should upgrade.

Security updates have been issued by Debian (mediawiki and unbound1.9), Fedora (djvulibre and samba), Mageia (ceph, messagelib, and pagure), openSUSE (alpine and exim), Oracle (kernel and postgresql), Scientific Linux (postgresql), and Ubuntu (thunderbird and unbound).

The second half of the interview with Linus Torvalds on the Tag1 Consulting site has been posted.

I think one of the reasons Linux succeeded was exactly the fact that I actually did NOT have a big plan, and did not have high expectations of where things would go, and so when people started sending me patches, or sending me requests for features, to me that was all great, and I had no preconceived notion of what Linux should be. End result: all those individuals (and later big companies) that wanted to participate in Linux kernel development had a fairly easy time to do so, because I was quite open to Linux doing things that I personally had had no real interest in originally.

Among the many changes merged for 5.13 can be found performance improvements throughout the kernel. This work does not always stand out the way that new features do, but it is vitally important for the future of the kernel overall. In the memory-management area, a couple of long-running patch sets have finally made it into the mainline; these provide a bulk page-allocation interface and huge-page mappings in the vmalloc() area. Both of these changes should make things faster, at least for some workloads.

Security updates have been issued by Debian (python-django), Fedora (java-latest-openjdk, libopenmpt, python-yara, skopeo, thunderbird, and yara), openSUSE (ceph and openexr), Red Hat (postgresql), SUSE (libxml2), and Ubuntu (exim4 and gnome-autoar).

The LWN.net Weekly Edition for May 6, 2021 is available.

The era of tracking users all across the web using third-party cookies is coming to a close; that type of cookie is something of a zombie at this point. All of the major browsers, save one, are blocking third-party cookies by default and the holdout, Google Chrome, plans to make that change next year. But Google, which has a business model built around advertising that benefits greatly from the status quo, has offered up an alternative scheme to "replace" third-party cookies. The Federated Learning of Cohorts (FLoC) is an in-browser mechanism to pigeonhole users in a way that will be useful to advertisers, but the only reason the idea has any traction at all is because it is being implemented in Chrome—the dominant browser today.

The Linux Foundation Technical Advisory Board has issued its report on the submission of (intentionally and unintentionally) buggy patches from the University of Minnesota.

This report summarizes the events that led to this point, reviews the "Hypocrite Commits" paper that had been submitted for publication, and reviews all known prior kernel commits from UMN paper authors that had been accepted into our source repository. It concludes with a few suggestions about how the community, with UMN included, can move forward.

The recommendations include establishing an internal review process for patches submitted by the community and the creation (by the TAB in cooperation with researchers) of a "best practices" document for researchers working with the kernel community.

(LWN editor Jonathan Corbet played a small part in the writing of this report).

Security updates have been issued by Debian (cgal, exim4, and mediawiki), Fedora (axel, libmicrohttpd, libtpms, perl-Image-ExifTool, pngcheck, python-yara, and yara), Gentoo (exim), Mageia (kernel-linus), openSUSE (bind and postsrsd), SUSE (avahi, openexr, p7zip, python-Pygments, python36, samba, sca-patterns-sle11, and webkit2gtk3), and Ubuntu (nvidia-graphics-drivers-390, nvidia-graphics-drivers-418-server, nvidia-graphics-drivers-450, nvidia-graphics-drivers-450-server, nvidia-graphics-drivers-460, nvidia-graphics-drivers-460-server).

The movement toward using memory-safe languages, and Rust in particular, has picked up a lot of steam over the past year or two. Removing the possibility of buffer overflows, use-after-free bugs, and other woes associated with unmanaged pointers is an attractive feature, especially given that the majority of today's vulnerabilities stem from memory-safety issues. On April 20, the Internet Security Research Group (ISRG) announced a funding initiative targeting the Rustls TLS library in order to prepare it for more widespread adoption—including by ISRG's Let's Encrypt project.

Security updates have been issued by Debian (bind9, chromium, exim4, and subversion), Fedora (exiv2 and skopeo), openSUSE (gsoap), Oracle (bind, kernel, and sudo), SUSE (bind, ceph, ceph, deepsea, permissions, and stunnel), and Ubuntu (clamav, exim4, openvpn, python-django, and samba).

There are, it seems, 21 vulnerabilities in the Exim email server that have been fixed in the 4.94.2 release; at least some of these are remotely exploitable for root access. "The current Exim versions (and likely older versions too) suffer from several exploitable vulnerabilities. These vulnerabilities were reported by Qualys via security@exim.org back in October 2020. Due to several internal reasons it took more time than usual for the Exim development team to work on these reported issues in a timely manner." See this advisory from Qualys for the details.

The Red Hat Developer Blog has posted an introduction to the rr debugger. "rr records trace information about the execution of an application. This information allows you to repeatedly replay a particular recording of a failure and examine it in the GNU Debugger (GDB) to better investigate the cause. In addition to replaying the trace, rr lets you run the program in reverse, in essence allowing you 'rewind the tape' to see what happened earlier in the execution of the program."

The kernel's control-group mechanism exists to partition processes and to provide resource guarantees (and limits) for each. Processes running within a properly configured control group are unable to deprive those running in a different group of their allocated resources (CPU time, memory, I/O bandwidth, etc.), and are equally protected from interference by others. With few exceptions, control groups are not used to take direct actions on processes; Christian Brauner's cgroup.kill patch set is meant to be one of those exceptions.

Security updates have been issued by CentOS (bind, GNOME, java-1.8.0-openjdk, java-11-openjdk, nss and nspr, xstream, and xterm), Debian (bind9 and libimage-exiftool-perl), Fedora (ansible, babel, java-11-openjdk, and java-latest-openjdk), Gentoo (chromium, clamav, firefox, git, grub, python, thunderbird, tiff, webkit-gtk, and xorg-server), Mageia (kernel, nvidia-current, nvidia390, qtbase5, and sdl2), openSUSE (Chromium, cifs-utils, cups, giflib, gsoap, libnettle, librsvg, netdata, postsrsd, samba, thunderbird, virtualbox, and webkit2gtk3), Red Hat (bind), Scientific Linux (bind), and SUSE (containerd, docker, runc and xen).