/*
* Common routine to check if an unprivileged mount is allowed.
*
* We export just this part (i.e., without the access control) so that if a
* secmodel wants to implement finer grained user mounts it can do so without
* copying too much code. More elaborate policies (i.e., specific users allowed
* to also create devices and/or introduce set-id binaries, or export
* file-systems) will require a different implementation.
*
* This routine is intended to be called from listener context, and as such
* does not take credentials as an argument.
*/