qubes-doc/security/vm-sudo.md

---
layout: doc
title: VM Sudo
permalink: /doc/vm-sudo/
redirect_from:
- /en/doc/vm-sudo/
- /doc/VMSudo/
- /wiki/VMSudo/
---

Password-less root access in VM
===============================

Background ([/etc/sudoers.d/qubes](https://github.com/QubesOS/qubes-core-agent-linux/blob/master/misc/qubes.sudoers) in VM):

    user ALL=(ALL) NOPASSWD: ALL

    # WTF?! Have you lost your mind?!
    #
    # In Qubes VMs there is no point in isolating the root account from
    # the user account. This is because all the user data is already
    # accessible from the user account, so there is no direct benefit for
    # the attacker if she could escalate to root (there is even no benefit
    # in trying to install some persistent rootkits, as the VM's root
    # filesystem modifications are lost upon each start of a VM).
    #
    # One might argue that some hypothetical attacks against the
    # hypervisor or the few daemons/backends in Dom0 (so VM escape
    # attacks) most likely would require root access in the VM to trigger
    # the attack.
    #
    # That's true, but mere existence of such a bug in the hypervisor or
    # Dom0 that could be exploited by a malicious VM, no matter whether
    # requiring user, root, or even kernel access in the VM, would be
    # FATAL. In such situation (if there was such a bug in Xen) there
    # really is no comforting that: "oh, but the mitigating factor was
    # that the attacker needed root in VM!" We're not M$, and we're not
    # gonna BS our users that there are mitigating factors in that case,
    # and for sure, root/user isolation is not a mitigating factor.
    #
    # Because, really, if somebody could find and exploit a bug in the Xen
    # hypervisor -- as of 2016, there have been only three publicly disclosed
    # exploitable bugs in the Xen hypervisor from a VM -- then it would be
    # incidentally by one of the Qubes developers (RW) -- then it would be
    # highly unlikely if that person couldn't also found a user-to-root
    # escalation in VM (which as we know from history of UNIX/Linux
    # happens all the time).
    #
    # At the same time allowing for easy user-to-root escalation in a VM
    # is simply convenient for users, especially for update installation.
    #
    # Currently this still doesn't work as expected, because some idotic
    # piece of software called PolKit uses own set of policies. We're
    # planning to address this in Beta 2. (Why PolKit is an idiocy? Do a
    # simple experiment: start 'xinput test' in one xterm, running as
    # user, then open some app that uses PolKit and asks for root
    # password, e.g.  gpk-update-viewer -- observe how all the keystrokes
    # with root password you enter into the "secure" PolKit dialog box can
    # be seen by the xinput program...)
    #
    # joanna.

Below is a complete list of configuration made according to the above statement, with (not necessary complete) list of mechanisms depending on each of them:

1.  sudo (/etc/sudoers.d/qubes):

        user ALL=(ALL) NOPASSWD: ALL
        (...)

    - easy user->root access (main option for the user)
    - qvm-usb (not really working, as of R2)

2.  PolicyKit (/etc/polkit-1/rules.d/00-qubes-allow-all.rules):

        //allow any action, detailed reasoning in sudoers.d/qubes
        polkit.addRule(function(action,subject) { return polkit.Result.YES; });

    and /etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla:

        [Qubes allow all]
        Identity=*
        Action=*
        ResultAny=yes
        ResultInactive=yes
        ResultActive=yes

    - NetworkManager configuration from normal user (nm-applet)
    - updates installation (gpk-update-viewer)
    - user can use pkexec just like sudo Note: above is needed mostly because Qubes user GUI session isn't treated by PolicyKit/logind as "local" session because of the way in which X server and session is started. Perhaps we will address this issue in the future, but this is really low priority. Patches welcomed anyway.

3.  Empty root password
    - used for access to 'root' account from text console (xl console) - the only way to access the VM when GUI isn't working
    - can be used for easy 'su -' from user to root

Replacing password-less root access with Dom0 user prompt
---------------------------------------------------------

While ITL supports the statement above, some Qubes users may wish to enable
user/root isolation in VMs anyway. We do not support it in any of our packages,
but of course nothing is preventing the user from modifying his or her own
system. A list of steps to do so is provided here **without any guarantee of
safety, accuracy, or completeness. Proceed at your own risk. Do not rely on
this for extra security.**

1. Adding Dom0 "VMAuth" service:

        [root@dom0 /]# echo "/usr/bin/echo 1" >/etc/qubes-rpc/qubes.VMAuth
        [root@dom0 /]# echo "\$anyvm dom0 ask,default_target=dom0" \
        >/etc/qubes-rpc/policy/qubes.VMAuth

   (Note: any VMs you would like still to have password-less root access (e.g. TemplateVMs) can be specified in the second file with "\<vmname\> dom0 allow")

2. Configuring Fedora TemplateVM to prompt Dom0 for any authorization request:
    - In /etc/pam.d/system-auth, replace all lines beginning with "auth" with these lines:

          auth  [success=1 default=ignore]  pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /bin/grep -q ^1$
          auth  requisite  pam_deny.so
          auth  required   pam_permit.so

    - Require authentication for sudo. Replace the first line of /etc/sudoers.d/qubes with:

          user ALL=(ALL) ALL

    - Disable PolKit's default-allow behavior:

          [root@fedora-20-x64]# rm /etc/polkit-1/rules.d/00-qubes-allow-all.rules
          [root@fedora-20-x64]# rm /etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla

3. Configuring Debian/Whonix TemplateVM to prompt Dom0 for any authorization request:
    - In /etc/pam.d/common-auth, replace all lines beginning with "auth" with these lines:

          auth  [success=1 default=ignore]  pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /bin/grep -q ^1$
          auth  requisite  pam_deny.so
          auth  required   pam_permit.so

    - Require authentication for sudo. Replace the first line of /etc/sudoers.d/qubes with:

          user ALL=(ALL) ALL

    - Disable PolKit's default-allow behavior:

          [root@debian-8]# rm /etc/polkit-1/rules.d/00-qubes-allow-all.rules
          [root@debian-8]# rm /etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla

    - In /etc/pam.d/su.qubes, comment out this line near the bottom of the file:

          auth sufficient pam_permit.so

    - For Whonix, if prompts appear during boot, create /etc/sudoers.d/zz99 and add these lines:

          ALL ALL=NOPASSWD: /usr/sbin/virt-what
          ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck restart
          ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck start
          ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck stop
          ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck status

Dom0 password-less root access
------------------------------

There is also password-less user->root access in dom0. As stated in comment in sudo configuration there (different one than VMs one), there is really no point in user/root isolation, because all the user data (and VM management interface) is already accessible from dom0 user level, so there is nothing more to get from dom0 root account.