Can unprivileged users corrupt the store with bad tarballs?

[Mark H Weaver]

I was thinking about the security implications of giving out shell
access to one of my systems running Guix.

When I ask guix-daemon to build package 'foo', it will use as an input
the source for package 'foo', usually a tarball.  If the tarball is
already in the store, it won't download it again, because it is
effectively cached in the store.

It is possible for another user on the same system to corrupt the cache,
but manually adding a bad tarball for 'foo' to the store, in such a way
that it would be used to build 'foo' when I ask for it?

      Mark