[throwaway15908]

On a broad scope, you could solve this at compile time. The source simply does not compile when filesystem or networking crates/builtins are not defined.

If you want to have more fine grained white listing, like only grant access to a certain directory, this could get really messy quick, trying to solve this at compile time.

[oconnor663]

You'd probably have to start by banning unsafe code in general, but then whitelisting/allowlisting specific versions of specific crates that are allowed to use it, so that at least the most popular dependencies don't break.