CVE-2022-48700

In the Linux kernel, the following vulnerability has been resolved:
vfio/type1: Unpin zero pages There’s currently a reference count leak on
the zero page. We increment the reference via pin_user_pages_remote(), but
the page is later handled as an invalid/reserved page, therefore it’s not
accounted against the user and not unpinned by our put_pfn(). Introducing
special zero page handling in put_pfn() would resolve the leak, but without
accounting of the zero page, a single user could still create enough
mappings to generate a reference count overflow. The zero page is always
resident, so for our purposes there’s no reason to keep it pinned.
Therefore, add a loop to walk pages returned from pin_user_pages_remote()
and unpin any zero pages.