fidzu : debian

Linux kernel security modules provide a good additional layer of security around individual programs by restricting what they are allowed to do, and at best block and detect zero-day security vulnerabilities as soon as anyone tries to exploit them, long before they are widely known and reported. However, the challenge is how to create these security profiles without accidentally also blocking legitimate actions. For MariaDB in Debian and Ubuntu, a new AppArmor profile was recently created by leveraging the extensive test suite with 7000+ tests, giving good confidence that AppArmor is unlikely to yield false positive alerts with it.

AppArmor is a Mandatory Access Control (MAC) system, meaning that each process controlled by AppArmor has a sort of an "allowlist" called profile that defines all capabilities and file paths a program can access. If a program tries to do something not covered by the rules in its AppArmor profile, the action will be denied on the Linux kernel level and a warning logged in the system journal. This additional security layer is valuable because even if a malicious user found a security vulnerability some day in the future, the AppArmor profile severely restricts the ability to exploit it and gain access to the operating system.

AppArmor was originally developed by Novell for use in SUSE Linux, but nowadays the main driver is Canonical and AppArmor is extensively used in Ubuntu and Debian, and many of their derivatives (e.g. Linux Mint, Pop!_OS, Zorin OS) and in Arch. AppArmor's benefit compared to the main alternative SELinux (used mainly in the RedHat/Fedora ecosystem) is that AppArmor is easier to manage. AppArmor continues to be actively developed, with new major version 5.0 expected to arrive soon.

I also have some personal history contributing some notification handler scripts in Python and I also created the website that AppArmor.net still runs.

Regular review of denials in the system log required

Any system administrator using Debian/Ubuntu needs to know how to check for AppArmor denials. The point of using AppArmor is kind of moot if nobody is checking the denials. When AppArmor blocks an action, it logs the event to the system audit or kernel logs. Understanding these logs is crucial for troubleshooting custom configurations or identifying potential security incidents.

To view recent denials, check /var/log/audit/audit.log or run journalctl -ke --grep=apparmor.

A typical denial entry for MariaDB will look like this (split across multiple lines for legibility):

msg=audit(1700000000.123:456): apparmor="DENIED" operation="open"
profile="/usr/sbin/mariadbd" name="/custom/data/path/test.ibd" pid=1234
comm="mariadbd" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0

How to interpret this output:

• msg=audit(…): The audit timestamp and event serial number.
• apparmor="DENIED": Indicates AppArmor blocked the action.
• operation: The action being attempted (e.g., open, mknod, file_mmap, file_perm).
• profile: The specific AppArmor profile that triggered the denial (in this case the /usr/sbin/mariadbd profile).
• name: The file path or resource that was blocked. In the example above, a custom data path was denied access because it wasn't defined in the profile's allowed abstractions.
• comm: The command name that triggered the denial (here mariadbd).
• requested_mask / denied_mask: Shows the permissions requested (e.g., r for read, w for write).
• pid: The process ID.
• fsuid: The user ID of the process attempting the action.
• ouid: The owner user ID of the target file.

If an action seems legit and should not be denied, the sysadmin needs to update the existing rules at /etc/apparmor.d/ or drop a local customization file in at /etc/apparmor.d/local/. If the denied action looks malicious, the sysadmin should start a security investigation and if needed report a suspected zero-day vulnerability to the upstream software vendor (e.g. Ubuntu customers to Canonical, or MariaDB customers to MariaDB).

AppArmor in MariaDB - not a novel thing, and not easy to implement well

Based on old bug reports, there was an AppArmor profile already back in 2011, but it was removed in MariaDB 5.1.56 due to backlash from users running into various issues. A new profile was created in 2015, but kept opt-in only due to the risk of side effects. It likely had very few users and saw minimal maintenance, getting only a handful of updates in the past 10 years.

The primary challenge in using mandatory access control systems with MariaDB lies in the sheer breadth of MariaDB's operational footprint with diverse storage engines and plugins. Also the code base in MariaDB assumes that system calls to Linux always work - which they do under normal circumstances - and do not handle errors well if AppArmor suddenly denies a system call. MariaDB is also a large and complex piece of software to run and operate, and it can be very challenging for system administrators to root-cause that a misbehavior in their system was due to AppArmor blocking a single syscall.

Ironically, AppArmor is most beneficial exactly due to the same reasons for MariaDB. The larger and more complex a software is, the larger are the odds of a security vulnerability arising between the various components. And AppArmor profile helps reduce this complexity down to a single access list.

Over the years there has been users requesting to get the AppArmor profile back, such as Debian Bug#875890 since 2017. The need was raised recently again by the Ubuntu security team during the MariaDB Ubuntu 'main' inclusion review in 2025, which prompted a renewed effort by Debian/Ubuntu developers, mainly myself and Aquila Macedo, with upstream MariaDB assistance from Daniel Black.

A fresh approach: leverage the MariaDB test suite for automated testing and the open source community for reviews

The key to creating a robust AppArmor profile is the ability to know in detail what is expected and normal behavior of the system. One could in theory read all of the source code in MariaDB, but with over two million lines, it is of course not feasible in practice. However, MariaDB does have a very extensive 7000+ test suite, and running it should trigger most code paths in MariaDB. Utilizing the test suite was key in creating the new AppArmor profile for MariaDB: we installed MariaDB on a Ubuntu system, enabled AppArmor in complain mode and iterated on the allowlist by running the full mariadb-test-run with all MariaDB plugins and features enabled until we had a comprehensive yet clean list of rules.

To be extra diligent, we also reworked the autopkgtest for MariaDB in Debian and Ubuntu CI systems to run with the AppArmor profile enabled and to print all AppArmor notices at the end of the run, making it easy to detect now and in the future if the MariaDB test suite triggers any AppArmor denials. If any test fails, the release would not get promoted further, protecting users from regressions.

While developing and triggering manual test runs we used the maximal achievable test suite with 7177 tests. The test is however so extensive it takes over two hours to run, and it also has some brittle tests, so the standard test run in Debian and Ubuntu autopkgtest is limited just to MariaDB's main suite with about 1000 tests. Having some tests fail while testing the AppArmor profile was not a problem, because we didn't need all the tests to pass - we merely needed them to run as many code paths as possible to see if they run any system calls not accounted for in the AppArmor profile.

Note that extending the profile was not just mechanical copying of log messages to the profile. For example, even though a couple of tests involve running the dash shell, we decided to not allow it, as it opens too much of a path for a potential exploit to access the operating system.

The result of this effort is a modernized, robust profile that is now production-ready. Those interested in the exact technical details can read the Debian Bug#1130272 and the Merge Request discussions at salsa.debian.org, which hosts the Debian packaging source code.

Now available in Debian unstable, soon Ubuntu - feedback welcome!

Even though the file is just 200 lines long, the work to craft it spanned several weeks. To minimize risk we also did a gradual rollout by releasing the first new profile version in complain mode, so AppArmor only logs would-be-denials without blocking anything. The AppArmor profile was switched to enforce mode only in the very latest MariaDB revision 1:11.8.6-4 in Debian, and a NEWS item issued to help increase user awareness of this change. It is also slated for the upcoming Ubuntu 26.04 "Resolute Raccoon" release next month, providing out-of-the-box hardening for the wider ecosystem.

While automated testing is extensive, it cannot simulate everything. Most notably various complicated replication topologies and all Galera setups are likely not covered. Thus, I am calling on the community to deploy this profile and monitor for any audit denials in the kernel logs. If you encounter unexpected behavior or legitimate denials, please submit a bug report via the Debian Bug Tracking System.

To ensure you are running the latest MariaDB version, run apt install --update --yes mariadb-server. To view the latest profile rules, run cat /etc/apparmor.d/mariadbd and to see if it is enforced review the output of aa-status. To quickly check if there were any AppArmor denials, simply run journalctl -k | grep -i apparmor | grep -i mariadb.

Systemd hardening also adopted as security features keep evolving

For those interested in MariaDB security hardening, note that also new systemd hardening options were rolled out in Debian/Ubuntu recently. Note that Debian and Ubuntu are mainly volunteer-driven open source developer communities, and if you find this topic interesting and you think you have the necessary skills, feel free to submit your improvement ideas as Merge Requests at salsa.debian.org/mariadb-team. If your improvement suggestions are not Debian/Ubuntu specific, please submit them directly to upstream at GitHub.com/MariaDB.

19 Mar 2026 12:00am GMT

And yet another maintenance release of the tidyCpp package arrived on CRAN this morning, just days after previous release which itself came a mere week and a half after its predecessor. It has been built for r2u as well. The package offers a clean C++ layer (as well as one small C++ helper class) on top of the C API for R which aims to make use of this robust (if awkward) C API a little easier and more consistent. See the vignette for motivating examples.

This release restores the small CSS file used by the vignette which we, in a last-second decision, omitted from the previous release. Oddly, it only failed under the 'oldrel' i.e. the R from now nearly two years ago. But it was still an unenforced error, and this upload corrects it.

Changes are summarized in the NEWS entry that follows.

Changes in tidyCpp version 0.0.11 (2026-03-17)

• Keep a CSS file in the package to allow vignette build on r-oldrel too

Thanks to my CRANberries, there is also a diffstat report for this release. For questions, suggestions, or issues please use the issue tracker at the GitHub repo.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. If you like this or other open-source work I do, you can now sponsor me at GitHub.

18 Mar 2026 8:49pm GMT

Between July and November 2025, the Debian pt_BR translation team received five students for an online mentoring program. The initiative was carried out in partnership with the Federal University of ABC through the extension project "Immersion in Free Software", coordinated by professors Suzana Santos and Miguel Vieira.

During the mentorship the mentees acted on several of the team's translation efforts and joined presentations about the Debian Project and its community given by the mentors. We thank the dedication and contributions of Ana Parra, Bruno Freitas, Henrique Barbosa, Raul Banzatto and Vitoria Cordeiro. And we also thank the members of the team who have reviewed the work of the mentees, specially the ones who were designated as official mentors, namely Allythy Rennan, Daniel Lenharo, Thiago Pezzo, and Victor Marinho.

Results:

• Package descriptions, translations: 27
• Package descriptions, revisions: 190
• Web pages: 11
• Revisions to the Debian Administrator's Handbook
• Revisions to the Debian Edu documentation

We hope that this experience will inspire new paths and that you continue to contribute to Free Software - especially to Debian.

18 Mar 2026 4:45pm GMT