xen/grants: prevent integer overflow in gnttab_dma_alloc_pages()

The change from kcalloc() to kvmalloc() means that arg->nr_pages
might now be large enough that the "args->nr_pages << PAGE_SHIFT" can
result in an integer overflow.

Fixes: b3f7931f5c61 ("xen/gntdev: switch from kcalloc() to kvcalloc()")
Signed-off-by: Dan Carpenter <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Link: https://lore.kernel.org/r/YxDROJqu/RPvR0bi@kili
Signed-off-by: Juergen Gross <[e-mail]>

drivers/xen/grant-table.c

···
 	size_t size;
 	int i, ret;
 
+	if (args->nr_pages < 0 || args->nr_pages > (INT_MAX >> PAGE_SHIFT))
+		return -ENOMEM;
+
 	size = args->nr_pages << PAGE_SHIFT;
 	if (args->coherent)
 		args->vaddr = dma_alloc_coherent(args->dev, size,