Notices by Lennart Poettering (pid_eins@mastodon.social), page 6

…supported JSON output anyway, the output side was done pretty much anyway.

Anyway, there are many other stories like that.

Suffice to say, in v257 there are now 19 Varlink interfaces/services, which we added in a short time, for various things that never had them before when D-Bus was our sole focus, because it was so nasty to add that.

(For comparison: we provide only 11 D-Bus API services at this time).

At Linux' best conference, All Systems Go! 2024 in Berlin this year I gave a (brief) talk about Varlink, and why you should consider it. If you want to know more about the concept, this might be a good starting point:

https://media.ccc.de/v/all-systems-go-2024-276-varlink-now-

And that's all for now, enjoy!

i.e. for example handles base64 encoding/decoding for handling binary blobs within JSON automatically, or it helps you with dealing with JSON's >53bit integer problem, and various other things.

Right now, documentation for sd-varlink and sd-json is scarce (one could even say "barely existing"), but there are plenty of real-life examples in the systemd source tree, of course.

3️⃣ Here's the 3rd installment of posts highlighting key new features of the upcoming v257 release of systemd.

So after the relatively heavy fare of the 2nd episode, here's something to digest more easily.

Since a while systemd has been showing nice terminal progress bars when doing certain slow operations (for example, when systemd-repart initializes a disk). With v257 we go one step further with this. Whenever we show the progress bar we'll now also issue certain terminal ANSI sequences …

… that tell your terminal emulator that a slow operation is going on and what the progress currently is.

The ANSI sequences for this are commonly used on Windows, where the new Windows Terminal implements them and paints a pretty little spinner on your terminal tab when they are issued. On Linux terminals the sequence is so far mostly ignored, but maybe it's time that changes? I think it's a truly useful feature because it can communicate progress information about slow operations to the user…

I think the pair of PID and pidfd inode number would be great to support in the various tools that currently deal with PIDs. For example, I filed an RFE bug against util-linux' kill tool to add just that:

https://github.com/util-linux/util-linux/issues/3252

… when we pass around information about processes via IPC we have started to do so via the triplet pid, pid inode, boot id.

And I'd recommend everyone dealing with low-level process management to do the same.

Two caveats though: the concept is not universal: it's a Linux thing, and it requires kernel 6.9 or newer and a 64bit architecture. On 32bit the inode number range is too small to provide unique IDs.

To properly check if the feature is available allocate a pidfd, and check if statfs() reports a .f_type field of it being 0x50494446. Also verify if sizeof(ino_t) is >= 8.

It took a long time, but thanks to @brauner after all those years the limitations of UNIX pid_t are addressed! Thanks, Christian!

@erincandescent cgroupfs actually exposes the cgroupid via ntha() and obha(). So yes, there's prior art for doing the same in pidfs. But it's a bit weird, because unlike cgroupfs pidfs is not an fs you can mount, hence you don't really have anything to invoke obha() on. You'd probably have to get a pidfd on your own pid first, before you can use it to use obha() to get to the pidfd you actually want to get to.

If you ask me, it's a fundamental requirement for any modern Linux-based OS to provide boot time integrity and as baseline provide unattended disk encryption bound to it. To make this happen, we added two essential TPM policy concepts to systemd-cryptenroll/systemd-cryptsetup:

1. Signed TPM PCR policies allow locking a disk to a public signing key of an OS vendor, ensuring that disks can only be unlocked if an OS signed by said vendor is booted.

2️⃣ Here's the 2nd installment of posts highlighting key new features of the upcoming v257 release of systemd.

In the past year and a bit I spent a lot of time on boot integrity (i.e. boot-time TPM measurements and policies built on top of them) of Linux, covering the boot from the boot loader (systemd-boot), over the UKI EFI stub (systemd-stub) through the initrd into early regular userspace, and then locking disk encryption to it.

There's a feature added to Linux 6.9 that I think people should become more aware of: there's finally an identifier for processes that doesn't wrap around as easily as UNIX pid_t PIDs do: the pidfd file descriptors have been moved onto their own proper file system (pidfs), which enabled at the same time unique inode numbers for them.

If you want a world-wide unique identifier for a process it makes sense to combine the pair of pid_t and pidfd inode number with the system's boot ID (i.e. /proc/sys/kernel/random/boot_id). This triplet is awesome, because for the first time we can uniquely identify a Linux process, globally in this universe.

In systemd we are making use of this heavily now: internally we always store a triplet of pid, pidfd, pidfd inode for referencing processes we manage and…

To query the inode number from a pidfd, you use a simple fstat() call, and look at the .st_ino field.

There's currently no way to get from a pidfd inode number directly to a process however. Hence, for now you always have to pass around a combination of classic PID and the new pidfd inode number. This can be safely and correctly be turned into a pidfd: 1. first acquire a pidfd from the PID via pidfd_open(). 2. Then fstat() the fd, and check if .st_ino matches the expected value.

These inode numbers are (at least on 64bit archs, i.e. anything modern) unique during the entire runtime of a system. And that's fantastic: there's finally a way how you can race-freely reference a process, with the ability to pass it around over any form of IPC, without risking that it suddenly starts to refer to some unintentended other process.

@josh after 15 years of TPMs and they becoming quite ubiquitious, I am still not seeing how they ever have been misused like this outside of theories and labs.

To me this appears to be mostly FUD from FSF/GNU.

I think if Linux OSes would actually start using TPMs properly, the net outcome for everyone would be *good*, and not bad. It would be much harder to gain persistence for an attacker, for example. And that's a massive benefit, for everyone.

@josh well, if you open up access to your logs (protected via measurements or not) to players you don't want to use them, it's kinda your own fault. Just don't do that. If you web browser passes quotes of your system to the web, it's a bug in the browser, not a problem of the TPM.

Every computing is dual-use, if you so will, I fail to see why this one should be more or less "dual-use" than anything else.

@duxsco yeah, I have doubts though that enrolling your own keys is something that can be made "just work" on general purpose PCs.

Yes, you can do it locally, if you know your hardware very well, or if you only care about VMs or so. But for the general population, I doubt self-enrolling is really an option. Too many problems given that hw extension cards provide signed firmware too.

@duxsco my own focus with systemd is definitely on providing generic components that help make any Linux based systems more secure. hence, I do care a lot about solutions that provide security and can be deployed on *generic* systems in the wild, without prior knowledge of what they provide or not. It's the "general population", or the broader IT ecosystem I care about, not some nerdy niche.