Comment by corty | Hacker News Reader

Comment by corty | Hacker News Reader

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Systemd provides a lot of network functionality in systemd-networkd, journald, timesyncd, etc. that is remote attack surface. All the systemd "cloud of daemons" is tightly coupled by dbus interfaces that enable an attacker to move from one exploited system service to the next. Even if the attacker doesn't manage to find an exploit in another system service, DoS is easily possible because the DBUS interfaces are quite fragile. Even as a benevolent admin it is easily possible to get the system into a state where e.g. clean shutdown is no longer possible because systemctl doesn't want to talk to systemd any longer and you cannot fix that. systemd-udevd also has raceconditions galore, so sending any message to it in the wrong order relative to another one will kill the system, maybe even open exploit vectors. At the very least I would, for hardening, recommend not using any network-facing systemd functionality.

And lines of code are not ridiculous, they are the best first-order estimate available. Of course an actual inspection of the code is better for a comparison, but that is a huge task. sloccount is quick and easy.

> Systemd provides a lot of network functionality in systemd-networkd, journald, timesyncd, etc. that is remote attack surface.

Everything systemd does is something the OS was already doing before, just using a bunch of independent-upstream-project daemons glued together with RC scripts. That attack-surface existed before. That LOC-count existed before. It just wasn't monolithic under one project/org, and so wasn't being perceived as a problem.

The various interactions between daemons, also weren't getting audited during upstream-project security audits, because all the interaction potential only existed in the downstream distribution, rather than being part of systemd's monolith + integration test-suite.

> DBUS interfaces are quite fragile

What, and what it replaced (arbitrary ug+w sockets in /var/run, speaking to custom one-off RPC-listener ABIs for each daemon) wasn't fragile?

IMHO, all that's changed is that there's more uniformity, meaning a single set of tools can be used to test+harden all such RPC interfaces, and security flaws can be fixed in one place (DBUS itself) rather than requiring theory-level descriptions of vulnerabilities to be communicated to each project, whereupon they're hopefully translated to separate one-off patches the affected daemon.

> systemd-udevd also has raceconditions galore, so sending any message to it in the wrong order relative to another one will kill the system, maybe even open exploit vectors

100% true of what came before it. Hell, some of my Linux systems from the 90s and early 2000s would lock up hard just because I `modprobe`d a webcam driver when the webcam was already USB-connected.

> What, and what it replaced (arbitrary ug+w sockets in /var/run, speaking to custom one-off RPC-listener ABIs for each daemon) wasn't fragile?

Sockets like initctl are far less fragile. You don't need a dbus-daemon that you can't restart if you cant talk to systemd. Your parser needs to recognise single-character commands instead of a complex rpc syntax plus an xml parser or javascript vm for filtering. You can't honestly believe DBUS isn't miles from the robustness of initctl.

> IMHO, all that's changed is that there's more uniformity, meaning a single set of tools can be used to test+harden all such RPC interfaces, and security flaws can be fixed in one place (DBUS itself) rather than requiring theory-level descriptions of vulnerabilities to be communicated to each project, whereupon they're hopefully translated to separate one-off patches the affected daemon.

Instead of easy-to-audit socket permissions you get a complex mess of xml and javascript filtering rules. This isn't progress in terms of security, its quite the opposite. Pounds of additional attack surface and additional obfuscation hindering defense.

What systemd gives is structure + consistency; service definitions are declarative and knowledge distro portable.

To me that that is the big benefit of systemd over sysV init.

> Pounds of additional attack surface

Again, show me a major in the wild exploit that abuses these supposed 'pounds of attack surface'. As was said before, systemd doesn't actually have that much new surface that wasn't there before. It's just before it was not maintained in any sort of organized manner but rather was scattered across tens of different projects in various state of no longer being actively maintained, as I said consolekit is a perfect example.

systemd is actually pretty modular. You don't have to run the components that are not useful to you thus limiting the attack surface greatly, if you're actually concerned about it.

I know some people have an allergic reaction to Poettering, but the guy's willing to touch some of the rotten parts of the ecosystems few others dear.

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