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any one of us if we sat on the OSSH team would flip the middle finger. What code is the project supposed to write when nothing on main dyn loaded liblzma. It was brought in from a patch they don't have realistic control over.

This is a Linux problem, and the problem is systemd, which is who brought the lib into memory and init'd it.

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> This is a Linux problem, and the problem is systemd, which is who brought the lib into memory and init'd it.

Not at all, it is a distro issue because a few distros such as Debian chose to patch openssh to bring in systemd support [1].

Other systemd-based distros like Arch Linux remains unaffected because they don't carry this patch.

1: https://sources.debian.org/src/openssh/1%3A9.7p1-2/debian/pa...

Yet Redhat and others applied this patch, as systemd is so incapable of reliably launching processes, that it kept killing sshd without it.

What a complete failure of an init system's job, and the patch was applied due to systemd not resolving the issue in another way.

This is the problem with systemd. Way, way way too much complexity.

systemd is just fine on Arch without this patch.

It's not a systemd issue, it's a larger cultural issue with packagers increasing attack surface to make their lives easier.

It absolutely, positively, 100% was added due to issues with systemd.

Both Redhat and Debian and others applied this patch as a result. People didn't do it "just cause".

https://bugzilla.redhat.com/show_bug.cgi?id=1381997

Jakub Jelen 2016-10-12 08:40:44 UTC

<snip>

> Why do you want to avoid sd_notify()?

Why to avoid this? Well, it is adding more systemd-specific bits and new build dependency to something that always worked well under other inits without any problems for years.

They chose the worst solution to a problem that had multiple better solutions because of a pre-existing patch was the easiest path forward. That’s exactly what I’m talking about.

I think the criticisms of systemd are valid but also tangential. I think Poettering himself is on one of the HN threads saying they didn't need to link to his library to accomplish what they sought to do. Lzma is also linked into a bunch of other critical stuff, including but not limited to distro package managers and the kernel itself, so if they didn't have sshd to compromise, they could have chosen another target.

And yet:

https://news.ycombinator.com/item?id=39878181

So no, as Pottering claimed, sshd would not be hit by this bug except for this systemd integration.

I really don't care about "Oh, someone could have written another compromise!". What allowed for this compromise, was a direct inability for systemd to reliable do its job as an init system, necessitating a patch.

And Redhat, Fedora, Debian, Ubuntu, and endless other distros took this route, because something was required, and here we are. Something that would not be required if systemd could actually perform its job as an init system without endless work arounds.

Also see my other reply in this thread, re Redhat's patch.

I'm not the type to go out of my way to defend systemd and their design choices. I'm just saying the severity of this scenario of a tainted library transcends some of the legit design criticisms. If you can trojan liblzma you can probably do some serious damage without systemd or sshd.

Of course you can trojan other ways, but that can only be said, in this thread, in defense of systemd.

After all, what you're saying is and has always been the case! It's like saying "Well, Ford had a design flaw in this Pinto, and sure 20 people died, but... like, cars have design flaws from time to time, so an accident like this would've happened eventually anyhow! Oh well!"

It doesn't jive in this context.

Directly speaking to this point, patched ssh was chosen for a reason. It was the lowest hanging fruit, with the greatest reward. Your speculation about other targets isn't unwarranted, but at the same time, entirely unvalidated.

I just went and read https://bugzilla.redhat.com/show_bug.cgi?id=1381997 and actually seems to me that sshd behavior is wrong, here. I agree with the S6 school of thought, i.e. that PID files are an abomination and that there should always be a chain of supervision. systemd is capable of doing that just fine. The described sshd behavior (re-execing in the existing daemon and then forking) can only work on a dumb init system that doesn't track child processes. PID files are always a race condition and should never be part of any service detection.

That said, there are dozens of ways to fix this and it really seems like RedHat chose the worst one. They could have patched sshd in the other various ways listed in that ticket, or even just patch it to exit on SIGHUP and let systemd re-launch it.

Brought in from a patch they rejected to accept because of this exact risk

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