vfio: checking of validity of user vaddr in vfio_dma_rw

instead of calling __copy_to/from_user(), use copy_to_from_user() to
ensure vaddr range is a valid user address range before accessing them.

Fixes: 8d46c0c ("vfio: introduce vfio_dma_rw to read/write a range of IOVAs")
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Reported-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -2345,10 +2345,10 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 	vaddr = dma->vaddr + offset;
 
 	if (write)
-		*copied = __copy_to_user((void __user *)vaddr, data,
+		*copied = copy_to_user((void __user *)vaddr, data,
 					 count) ? 0 : count;
 	else
-		*copied = __copy_from_user(data, (void __user *)vaddr,
+		*copied = copy_from_user(data, (void __user *)vaddr,
 					   count) ? 0 : count;
 	if (kthread)
 		unuse_mm(mm);