xen/memory: Fix compat XENMEM_acquire_resource for size requests

Copy the nr_frames from the structure which actually has the correct value, so
the caller doesn't unconditionally receive 0.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
master commit: 414be7b663
master date: 2021-01-12 18:17:02 +0000

xen/common/compat/memory.c

@@ -599,7 +599,7 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) compat)
                 if ( __copy_field_to_guest(
                          guest_handle_cast(compat,
                                            compat_mem_acquire_resource_t),
-                         &cmp.mar, nr_frames) )
+                         nat.mar, nr_frames) )
                     return -EFAULT;
             }
             else