hw/cxl: Ensuring enough data to read parameters in cmd_tunnel_management_cmd()

If len_in is less than the minimum spec allowed value, then return
CXL_MBOX_INVALID_PAYLOAD_LENGTH

Reported-by: Esifiel <esifiel@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20241101133917.27634-8-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/cxl/cxl-mailbox-utils.c

@@ -151,6 +151,9 @@ static CXLRetCode cmd_tunnel_management_cmd(const struct cxl_cmd *cmd,
     in = (void *)payload_in;
     out = (void *)payload_out;
 
+    if (len_in < sizeof(*in)) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
     /* Enough room for minimum sized message - no payload */
     if (in->size < sizeof(in->ccimessage)) {
         return CXL_MBOX_INVALID_PAYLOAD_LENGTH;