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by josephcsible·8mo ago·view on hn ↗
> But today, couldn't we just open up a mount namespace and bind-mount something else to /tmp, like SystemDs private tempdirs?

No, because unless you're already root (in which case you wouldn't have needed the binary with the capability in the first place), you can't make a mount namespace without also making a user namespace, and the counterproductive risk-averse craziness has led to removing unprivileged users' ability to make user namespaces.

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It's probably true that there are setuid programs that can be exploited if you run them in a user namespace. You probably need to remove setuid (and setgid) as Plan9 did in order to do this.
I meant distros are moving towards no unprivileged user namespaces at all, not just no setuid programs inside them.
Is "just no setuid programs inside them" even an option?