--- 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 -- so far there have been only one (!) publicly disclosed # exploitable bug in the Xen hypervisor from a VM, found in 2008, # 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 -n "/usr/bin/echo 1" >/etc/qubes-rpc/qubes.VMAuth [root@dom0 /]# echo -n "$anyvm dom0 ask" >/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 "\ 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 one line: auth [success=done default=die] pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /usr/bin/grep -q ^1$ - 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 one line: auth [success=done default=die] pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /bin/grep -q ^1$ - 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, comment out this line near the bottom of the file: auth sufficient pam_permit.so 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.