virtio_console: Assure used length from device is limited

stable inclusion
from linux-4.19.198
commit b5fba782ccd3d12a14f884cd20f255fc9c0eec0c

--------------------------------

[ Upstream commit d00d8da5 ]

The buf->len might come from an untrusted device. This
ensures the value would not exceed the size of the buffer
to avoid data corruption or loss.
Signed-off-by: NXie Yongji <xieyongji@bytedance.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210525125622.1203-1-xieyongji@bytedance.comSigned-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/char/virtio_console.c

@@ -488,7 +488,7 @@ static struct port_buffer *get_inbuf(struct port *port)
 
 	buf = virtqueue_get_buf(port->in_vq, &len);
 	if (buf) {
-		buf->len = len;
+		buf->len = min_t(size_t, len, buf->size);
 		buf->offset = 0;
 		port->stats.bytes_received += len;
 	}
@@ -1738,7 +1738,7 @@ static void control_work_handler(struct work_struct *work)
 	while ((buf = virtqueue_get_buf(vq, &len))) {
 		spin_unlock(&portdev->c_ivq_lock);
 
-		buf->len = len;
+		buf->len = min_t(size_t, len, buf->size);
 		buf->offset = 0;
 
 		handle_control_message(vq->vdev, portdev, buf);