Features/ServicesPrivateTmp

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Contents

Feature Name

Change several dangerous domains to use PrivateTmp in their unit file.

Summary

Run some services started by systemd with a private /tmp directory. This would mitigate the chance of a service making a mistake with how it handles its /tmp data allowing a user on the system to get a privilege escalation, since users would not have access to the services /tmp directory.


Owner

  • Email: dwalsh@redhat.com

Current status

  • Targeted release: [Fedora 17]
  • Last updated: Tue Feb 15 2012
  • Percentage of completion: 100%


Detailed Description

It seems to be a weekly occurrence of a new CVE for some app that uses /tmp insecurely.

Privileged services should stop using /tmp and /var/tmp. These services can potentially be interfered by unprivileged users, potentially leading to process escalation. The only server applications that need to use /tmp should be for communicating with users. For example the X server, and potentially apps that use kerberos for example sssd and nfs.gssd. (Although maybe at some point we need to fix this.) Most apps that rely on using /tmp to communicate with the user can be easily broken by users having individual /tmp using pam_namespace.

systemd as of Fedora 16 has the ability to run system services with private /tmp. I would like to propose that we change most of the services that use /tmp to use PrivateTmp in Fedora 17. In the unit file, this is done with:

[Service]
PrivateTmp=true

I have opened 48 bugs along with the blocker bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=782466

as a blocker bug for tracking system services that I believe use /tmp.

    • Note. systemd in Fedora 16 is currently broken. This feature requires systemd-38

Benefit to Fedora

Fedora systems would be more secure, and mitigated against /tmp privilege escalation.

Scope

This bugzilla is a blocker on all services that need to change their service unit file to include PrivateTmp=True

https://bugzilla.redhat.com/show_bug.cgi?id=782466

How To Test

Administrators that expect to find services /tmp data in /tmp will have to look in a new location. Sharing data via /tmp from a user to a system service or vice versa might be broken.

Documentation

Release Notes

Comments and Discussion