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

lang	layout	permalink	redirect_from	ref	title
en	doc	/doc/vm-sudo/	/en/doc/vm-sudo/ /doc/VMSudo/ /wiki/VMSudo/	165	Passwordless root access in qubes

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 the Qubes developers support the statement above, some Qubes users may wish to enable user/root isolation in VMs anyway. We do not support this in any of our packages, but of course nothing is preventing a user from modifying his or her own system. A list of steps to do so is provided in the Qubes community guide, Replacing passwordless root with a dom0 prompt without any guarantee of safety, accuracy, or completeness. Proceed at your own risk. Do not rely on this for extra security.

Dom0 passwordless root access

There is also passwordless user->root access in dom0. As stated in the comment in sudo configuration there (which is different from the one in individual qubes), 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.