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189 lines
7.2 KiB
Markdown
189 lines
7.2 KiB
Markdown
---
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lang: en
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layout: doc
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permalink: /doc/vm-sudo/
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redirect_from:
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- /en/doc/vm-sudo/
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- /doc/VMSudo/
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- /wiki/VMSudo/
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ref: 165
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title: Passwordless root access in qubes
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---
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Background (`/etc/sudoers.d/qubes` in VM):
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```
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user ALL=(ALL) NOPASSWD: ALL
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# WTF?! Have you lost your mind?!
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#
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# In Qubes VMs there is no point in isolating the root account from
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# the user account. This is because all the user data is already
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# accessible from the user account, so there is no direct benefit for
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# the attacker if she could escalate to root (there is even no benefit
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# in trying to install some persistent rootkits, as the VM's root
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# filesystem modifications are lost upon each start of a VM).
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#
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# One might argue that some hypothetical attacks against the
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# hypervisor or the few daemons/backends in Dom0 (so VM escape
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# attacks) most likely would require root access in the VM to trigger
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# the attack.
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#
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# That's true, but mere existence of such a bug in the hypervisor or
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# Dom0 that could be exploited by a malicious VM, no matter whether
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# requiring user, root, or even kernel access in the VM, would be
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# FATAL. In such situation (if there was such a bug in Xen) there
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# really is no comforting that: "oh, but the mitigating factor was
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# that the attacker needed root in VM!" We're not M$, and we're not
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# gonna BS our users that there are mitigating factors in that case,
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# and for sure, root/user isolation is not a mitigating factor.
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#
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# Because, really, if somebody could find and exploit a bug in the Xen
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# hypervisor -- as of 2016, there have been only three publicly disclosed
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# exploitable bugs in the Xen hypervisor from a VM -- then it would be
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# highly unlikely if that person couldn't also found a user-to-root
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# escalation in VM (which as we know from history of UNIX/Linux
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# happens all the time).
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#
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# At the same time allowing for easy user-to-root escalation in a VM
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# is simply convenient for users, especially for update installation.
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#
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# Currently this still doesn't work as expected, because some idotic
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# piece of software called PolKit uses own set of policies. We're
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# planning to address this in Beta 2. (Why PolKit is an idiocy? Do a
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# simple experiment: start 'xinput test' in one xterm, running as
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# user, then open some app that uses PolKit and asks for root
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# password, e.g. gpk-update-viewer -- observe how all the keystrokes
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# with root password you enter into the "secure" PolKit dialog box can
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# be seen by the xinput program...)
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#
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# joanna.
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```
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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:
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1. sudo (`/etc/sudoers.d/qubes`):
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```
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user ALL=(ALL) NOPASSWD: ALL
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(...)
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```
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- Easy user -> root access (main option for the user).
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- `qvm-usb` (not really working, as of R2).
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2. PolicyKit (`/etc/polkit-1/rules.d/00-qubes-allow-all.rules`):
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```
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//allow any action, detailed reasoning in sudoers.d/qubes
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polkit.addRule(function(action,subject) { return polkit.Result.YES; });
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```
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and `/etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla`:
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```
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[Qubes allow all]
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Identity=*
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Action=*
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ResultAny=yes
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ResultInactive=yes
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ResultActive=yes
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```
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- NetworkManager configuration from normal user (`nm-applet`).
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- Updates installation (`gpk-update-viewer`).
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- 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.
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Perhaps we will address this issue in the future, but this is really low priority.
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Patches welcomed anyway.
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3. Empty root password:
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- Used for access to 'root' account from text console (`qvm-console-dispvm`) - the only way to access the VM when GUI isn't working.
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- Can be used for easy 'su -' from user to root.
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Replacing passwordless root access with Dom0 user prompt
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--------------------------------------------------------
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While ITL supports the statement above, some Qubes users may wish to enable user/root isolation in VMs anyway.
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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.
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A list of steps to do so is provided here **without any guarantee of safety, accuracy, or completeness.
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Proceed at your own risk.
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Do not rely on this for extra security.**
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1. Adding Dom0 "VMAuth" service:
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```
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[root@dom0 /]# echo "/usr/bin/echo 1" >/etc/qubes-rpc/qubes.VMAuth
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[root@dom0 /]# echo "@anyvm dom0 ask,default_target=dom0" \
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>/etc/qubes-rpc/policy/qubes.VMAuth
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```
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(Note: any VMs you would like still to have passwordless root access (e.g. Templates) can be specified in the second file with "\<vmname\> dom0 allow")
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2. Configuring Fedora template to prompt Dom0 for any authorization request:
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- In `/etc/pam.d/system-auth`, replace all lines beginning with "auth" with these lines:
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```
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auth [success=1 default=ignore] pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /bin/grep -q ^1$
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auth requisite pam_deny.so
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auth required pam_permit.so
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```
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- Require authentication for sudo.
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Replace the first line of `/etc/sudoers.d/qubes` with:
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```
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user ALL=(ALL) ALL
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```
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- Disable PolKit's default-allow behavior:
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```
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[root@fedora-20-x64]# rm /etc/polkit-1/rules.d/00-qubes-allow-all.rules
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[root@fedora-20-x64]# rm /etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla
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```
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3. Configuring Debian/Whonix template to prompt Dom0 for any authorization request:
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- In `/etc/pam.d/common-auth`, replace all lines beginning with "auth" with these lines:
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```
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auth [success=1 default=ignore] pam_exec.so seteuid /usr/lib/qubes/qrexec-client-vm dom0 qubes.VMAuth /bin/grep -q ^1$
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auth requisite pam_deny.so
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auth required pam_permit.so
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```
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- Require authentication for sudo.
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Replace the first line of `/etc/sudoers.d/qubes` with:
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```
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user ALL=(ALL) ALL
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```
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- Disable PolKit's default-allow behavior:
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```
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[root@debian-8]# rm /etc/polkit-1/rules.d/00-qubes-allow-all.rules
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[root@debian-8]# rm /etc/polkit-1/localauthority/50-local.d/qubes-allow-all.pkla
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```
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- In `/etc/pam.d/su.qubes`, comment out this line near the bottom of the file:
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```
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auth sufficient pam_permit.so
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```
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- For Whonix, if prompts appear during boot, create `/etc/sudoers.d/zz99` and add these lines:
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```
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ALL ALL=NOPASSWD: /usr/sbin/virt-what
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ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck restart
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ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck start
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ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck stop
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ALL ALL=NOPASSWD: /usr/sbin/service whonixcheck status
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```
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Dom0 passwordless root access
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-----------------------------
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There is also passwordless user->root access in dom0.
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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.
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