[PATCH] virtio: console: check the control packet size before parsing it

[Guanglei Zhu <zhugl3@xiaopeng.com>]

The control queue handler hands whatever the host wrote to the
control queue straight to the parser:

	buf->len = min_t(size_t, len, buf->size);
	buf->offset = 0;

	handle_control_message(vq->vdev, portdev, buf);

handle_control_message() casts the start of the buffer to struct
virtio_console_control and reads the id, event and value fields
without ever looking at buf->len. A control packet shorter than the
structure makes the driver parse whatever bytes were left in the
reused buffer as a control header, and the uninitialized event then
drives the port state machine.

Drop control packets that are too short to hold the header.

Fixes: 17634ba25544 ("virtio: console: Add a new MULTIPORT feature, support for generic ports")
Cc: stable@vger.kernel.org
Signed-off-by: Guanglei Zhu <zhugl3@xiaopeng.com>
---
 drivers/char/virtio_console.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 019bcae81af5..5e2a4403dbf8 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1597,6 +1597,12 @@ static void handle_control_message(struct virtio_device *vdev,
 	size_t name_size;
 	int err;
 
+	if (buf->len < sizeof(struct virtio_console_control)) {
+		dev_dbg(&portdev->vdev->dev,
+			"Invalid control packet size %zu\n", buf->len);
+		return;
+	}
+
 	cpkt = (struct virtio_console_control *)(buf->buf + buf->offset);
 
 	port = find_port_by_id(portdev, virtio32_to_cpu(vdev, cpkt->id));
-- 
2.50.1