Insight gained from reading a paper titled "ACLs don't" that is really obvious in retrospect:

the confused deputy problem happens exactly because authority-based systems care about the authority of whoever directly performs an operation, and that intuition/model breaks when there's a *delegation*, i.e. with deputies.

It would be possible to deal with simple delegation, but it won't work when there are multiple levels of it or when there are complex delegation graphs.


This is beautiful and I've never thought about this before:

the convention we have in Unix to pass pre-opened stdin/stdout/stderr fds is not just a nice way to tell the program where to read its input from and output its result/logs to; it is exactly how capability passing should work in a capability-based system. This also is another reason why accepting an -o option (for "output file") is a bad idea.

Also, this is how socket activation works. systemd (or launchd, or inetd, or what have you) listens on a port or a Unix socket — because, being root, it has rights to. Then it passes a capability — either the bound socket fd, or an individual connection fd — when starting your service. Your service then doesn't have to be privileged, because it doesn't need to be able to open/bind the port/socket.

OMG! I already knew CSRF is also a Confused Deputy problem, but I didn't realize that CSRF-protection tokens are a way of introducing capability-based secutiry into the play. And again once you realize it it makes so much sense.

Damn, this paper is pure gold.

@bugaevc one of the features i love about systemd. i think launchd does it well too.

@xj9 yes; launchd even does this for Mach services. But that's not any news, what is news to me is the realization that this is basically capability passing!

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