libvhost-user.c: add assertion to vu_message_read_default

Explain Coverity that we are not going to overflow vmsg->fds.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-Id: <20230925194040.68592-5-vsementsov@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -322,6 +322,7 @@ vu_message_read_default(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
         if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
             fd_size = cmsg->cmsg_len - CMSG_LEN(0);
             vmsg->fd_num = fd_size / sizeof(int);
+            assert(fd_size < VHOST_MEMORY_BASELINE_NREGIONS);
             memcpy(vmsg->fds, CMSG_DATA(cmsg), fd_size);
             break;
         }