user-sysmaint-split

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user-sysmaint-split - Role-Based Boot Modes - Persistent User / Live user / Persistent sysmaint (system maintenance) and their use cases.

This is a concept still in development. Waiting for implementation. Help welcome!

Introduction[edit]

This page discusses different boot modes in the Kicksecure operating system, aimed at improving security through role-based boot options. It describes modes like "Persistent User" for daily activities and "Persistent System Maintenance (sysmaint)" for updates, software installation, and full system control. The goal is to isolate user activities and reduce security risks by restricting what each boot mode can access and modify. The page also explains potential opt-outs for users who prefer traditional root access.

These schemes are generic and work for both hosts and VMs. This applies to Kicksecure and derivatives of Kicksecure, such as Whonix®.

Development Goals[edit]

These goals guide the boot modes implementation:

Grub Default Boot Menu Entries[edit]

The default GRUB boot menu entries are:

  • PERSISTENT mode USER (For daily activities.)
  • LIVE mode USER (For daily activities.)
  • PERSISTENT mode SYSMAINT (For system maintenance.)

Use Cases for the Different Boot Modes[edit]

Common use cases tailored to the available boot modes:

  • PERSISTENT mode USER (For daily activities.):
    • Ideal for browsing, email, chat, or running a pre-configured server.
    • read-only /usr, /etc.
    • read-write /home
    • Verified Boot: enabled. (Planned.)
  • LIVE mode USER (For daily activities.): Similar to Persistent User but without persistence.
  • PERSISTENT mode SYSMAINT (For system maintenance..): Allows running sudo apt install [package], editing /etc/apt/sources.list.d, and similar tasks. Reboot into USER mode afterward.
    • read-write /usr, /etc, /home
    • Verified Boot: disabled

Boot Modes Comparison Table[edit]

Feature PERSISTENT mode USER LIVE mode USER PERSISTENT mode SYSMAINT
Description For daily activities such as browsing, email, chat, or running a pre-configured server. Similar to Persistent User but without persistence. For system maintenance tasks such as running sudo apt install [package], editing /etc/apt/sources.list.d, and similar tasks. Reboot into USER mode afterward.
File System Access: /usr, /etc No, read-only No, read-only Yes, read-write
File System Access: /home Yes, read-write No, read-only Yes, read-write
Verified Boot (planned) Yes, Enabled Yes, Enabled No, Disabled

Integration with Verified Boot[edit]

When booting into PERSISTENT mode SYSMAINT, verified boot will be disabled for the purpose of updates, software installation, and system configuration. During shutdown, the checksums required for verified boot will be created.

When booting into USER, verified boot will be enabled for the purpose of improved security.

See also Verified Boot for User but not for sysmaint.

planned: Role-Based Boot Modes (user versus sysmaint) will be implemented first. Verified boot is an additional security feature that is planned to be implemented later.

No Access to Privilege Escalation Tools for Limited Users[edit]

There are conceptually two groups of users, sysmaint users and limited users.

sysmaint users:

  • root
  • sysmaint

Limited users:

  • user
  • nginx
  • mysql
  • sdwdate
  • ntp
  • Not a member of groups root, sudo, or wheel.
  • etc.

It is planned that,

  • A) user "user" is no longer a member of group sudo by default, and;
  • B) limited Linux user accounts such as user "user" will no longer have access to any of the following Privilege Escalation Tools applications:
    • sudo
    • su
    • doas
    • pkexec

This is because Privilege Escalation Tools are SUID applications, which can be a security risk for local privilege escalation (such as from user to root). SUID related risks are elaborated on the SUID Disabler and Permission Hardener wiki page.

Prerequisite Knowledge:

  • Linux file system permission basics.
  • owner (u)
  • group (g)
  • others (o) (public)
  • read (r)
  • write (w)
  • execute (x)

Comparison:

Debian: Privilege Escalation Tools (such as sudo and similar programs) are, as per Debian default, owned by user root and group root. These can be read and execute by owner, group, and others. (chmod 755)

chmod-calc /usr/bin/sudo 

Permissions for: /usr/bin/sudo
Type: Regular File
Owner: root
Group: root
Octal Permissions: 755
File Size: 281624 bytes
Link Count: 1
Hidden File: No
ACLs: none
Extended Attributes: none
Capabilities: None
Immutable (chattr +i): No

Category   Read   Write  Execute 
Owner      Yes    Yes    Yes     
Group      Yes    No     Yes     
Public     Yes    No     Yes     

Special Attributes:
SUID: Set
SGID: Not Set
Sticky Bit: Not Set

Kicksecure Future: Privilege Escalation Tools will be owned by group sysmaint. others (which includes user user) will no longer have read or execute rights. (chown root:sysmaint /usr/bin/sudo; chmod o-rw /usr/bin/sudo; same for /bin/sudo) 

Group: sysmaint

Category   Read   Write  Execute 
Owner      Yes    Yes    Yes     
Group      Yes    No     Yes     
Public     No     No     No

Implementation Plan:

For this to happen, applications may no longer internally use sudo exceptions (e.g., /etc/sudoers.d). This is further detailed on the Dev/sudo page.

Opt-Out to Get the Same Behavior as Old Kicksecure[edit]

Users who wish "the old Kicksecure" "with unrestricted sudo for user user" back, who don't want the

  • PERSISTENT mode SYSMAINT (For system maintenance tasks.)

boot option, could uninstall package user-sysmaint-split. It could be easily removed using dummy-dependency.

dummy-dependency --purge user-sysmaint-split

(dummy-dependency is being used to avoid issues with meta package removal.)

Boot Modes Considered Too Unimportant to Be Added to GRUB Default Boot Menu[edit]

Currently, we don’t see good use cases to include these modes as default, but user feedback could change this in the future.

  • LIVE mode SYSMAINT

DIY Methods to Include These and Other Entries in the GRUB Boot Menu

A Files in the /etc/grub.d/ folder could add these entries, but they could be non-executable by default. To opt-in, users could run sudo chmod +x /etc/grub.d/somenumber_name-of-boot-mode.

B Users wanting custom entries can add them directly to the /etc/grub.d/ folder or GRUB boot menu.

C Using GRUB boot menu editing (key e) at boot, kernel parameters can be adjusted for any combination.

/etc/grub.d File Names[edit]

Details about /etc/grub.d files: 

filename                                     purpose
---------------------------------------      -----------------------------
/etc/grub.d/10_linux                         PERSISTENT mode USER
/etc/grub.d/11_linux_live                    LIVE mode USER
/etc/grub.d/12_linux_sysmaint                PERSISTENT mode SYSMAINT

Files should remain in lexical order below /etc/grub.d/20_ to avoid conflicts with existing scripts.

Note: Some files may not be created initially (or at all), as outlined in the "Boot Modes Considered Too Unimportant to Be Added to GRUB Default Boot Menu" section.

Server Support[edit]

GRUB boot menus aren’t easily accessible on many servers. A solution for making these boot modes available on servers is yet to be determined.

user-sysmaint-split will not be installed by default on servers. Meta package kicksecure-host-xfce will come with user-sysmaint-split by default but meta package kicksecure-host-cli won't.

Future work ideas:

Qubes Support[edit]

Package qubes-core-agent-passwordless-root will be no longer installed by default in Kicksecure for Qubes.

Todo[edit]

issues with sysmaint mode:

  • systemd units running providing attack surface (think long running file downloads/uploads)
  • start menu offering Firefox etc.
  • ability to run Firefox etc. from the terminal emulator

ideas:

  • minimal GUI
  • chroot based: complex, messy, two systems to upgrad
    • You have to get the disk mounts just right or else you will end up with bootloader upgrades and the like failing
    • You have to potentially deal with encryption and LVM, maybe even RAID and other weird setups
    • You have two systems to update, which is hard
  • a target similar to single user mode but not really single user mode to avoid issues with real single user mode
  • start minimal services only when booting into sysmaint mode
  • Start Menu: Hide Firefox and other similar applications when booting into sysmaint mode.
  • A systray icon could display an sysmaint symbol to indicate the mode.
  • Add a warning:
    • When starting Firefox in sysmaint mode, a popup message should inform the user to avoid browsing the internet unless absolutely necessary.
  • Address the challenge of reading documentation after booting into sysmaint mode:
    • Why read documentation in sysmaint mode?
      • This is often necessary when performing complex system maintenance tasks.
      • For online searches or resolving issues.
      • Using AI assistants.
      • Posting on forums.

Offline Documentation is helpful but an insufficient solution.

  • Offline documentation often links extensively to upstream resources.
  • Users are encouraged to look up online documentation whenever possible (referring to upstream resources).

Alternatives:

  • Ideally, users should perform such tasks on a separate computer.
  • These alternatives might seem impractical but are safer.
  • A less ideal, but safer option is to use a VM for such tasks.

Implementation[edit]

Prior Versions[edit]

Older concept version still containing "SUPERADMIN" and "SECUREADMIN".archive.org

Tickets[edit]

Related[edit]

Attribution[edit]

Kicksecure is an Implementation of the Securing Debian Manual. This chapter has been inspired by: Securing Debian Manualarchive.org, chapter Mounting partitions the right wayarchive.org


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