qubes-doc/user/security-in-qubes/vm-sudo.md

---
lang: en
layout: doc
permalink: /doc/vm-sudo/
redirect_from:
- /en/doc/vm-sudo/
- /doc/VMSudo/
- /wiki/VMSudo/
ref: 165
title: Passwordless Root Access in VMs
---

Passwordless Root Access in VMs
===============================

Background (`/etc/sudoers.d/qubes` 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
# 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 (`qvm-console-dispvm`) - the only way to access the VM when GUI isn't working.
    - Can be used for easy 'su -' from user to root.

Replacing passwordless 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 passwordless 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 passwordless root access
-----------------------------

There is also passwordless 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.