root access a VM without root password

so here is how to get into your VMs without knowing the root pass or having the ssh key to reach them. 

Basically we are going to mount a qemu disk image and make the changes needed. 

In order to mount a QUMU / KVM disk image you need to use qemu-nbd, which lets you use the NBD protocol to share the disk image on the network.

sudo modprobe nbd max_part=8
sudo qemu-nbd -c /dev/nbd0 -P 1 /var/lib/libvirt/images/img_name.qcow2
sudo mount /dev/nbd0p1 /mnt/kvm

Do whatever change you need to do (i.e. to have root access on ubuntu change the /etc/ssh/sshd_config file + the /etc/shadow with the appropriate hash of the pass)

sudo umount /mnt/kvm
sudo nbd-client -d /dev/nbd0

That's it.
Hope this helps Alex Barchiesi