usb: cdc-wdm: use memdup_user

Use memdup_user() helper instead of open-coding to simplify the code.
Signed-off-by: NGeliang Tang <geliangtang@gmail.com>
Acked-by: NOliver Neukum <oneukum@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-wdm.c

@@ -361,17 +361,9 @@ static ssize_t wdm_write
 	if (we < 0)
 		return usb_translate_errors(we);
 
-	buf = kmalloc(count, GFP_KERNEL);
-	if (!buf) {
-		rv = -ENOMEM;
-		goto outnl;
-	}
-
-	r = copy_from_user(buf, buffer, count);
-	if (r > 0) {
-		rv = -EFAULT;
-		goto out_free_mem;
-	}
+	buf = memdup_user(buffer, count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
 
 	/* concurrent writes and disconnect */
 	r = mutex_lock_interruptible(&desc->wlock);
@@ -441,8 +433,7 @@ static ssize_t wdm_write
 
 	usb_autopm_put_interface(desc->intf);
 	mutex_unlock(&desc->wlock);
-outnl:
-	return rv < 0 ? rv : count;
+	return count;
 
 out_free_mem_pm:
 	usb_autopm_put_interface(desc->intf);