gnttab: fix releasing of memory upon switches between versions

gnttab: fix releasing of memory upon switches between versions

gnttab_unpopulate_status_frames() incompletely freed the pages
previously used as status frame in that they did not get removed from
the domain's xenpage_list, thus causing subsequent list corruption
when those pages did get allocated again for the same or another purpose.

Similarly, grant_table_create() and gnttab_grow_table() both improperly
clean up in the event of an error - pages already shared with the guest
can't be freed by just passing them to free_xenheap_page(). Fix this by
sharing the pages only after all allocations succeeded.

This is CVE-2012-5510 / XSA-26.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>