Kernel security and update policy for post-release trees

This document describes the process and criteria for post-release kernel updates. The kernel is a very complex source package, and it is fundamentally different than other packages in the archive. The described process and criteria are built on the normal StableReleaseUpdates document, and where these documents conflict, this document takes precedence.

What sort of updates are allowed for post-release kernels?

In addition to the generic SRU requirements, we will accept patches which fall into any of the following categories:

1. It fixes a critical issue (data-loss, OOPs, crashes) or is security related. Security related issues might be covered by security releases which are special in handling and publication.

2. Simple, obvious and short fixes or hardware enablement patches. If there is a related upstream stable tree open (see below) this class of patches is required to come through the upstream process. Patches sent upstream for that reason must include their BugLink reference.

3. The patch is included in a corresponding upstream stable or extended stable release. For the lifetime of both LTS and non-LTS releases we will be pulling upstream stable updates from the corresponding series. There will be one tracking bug report for each stable update but additional references to existing bugs will be added to the contained patches (on best can do base).
4. Fixes to drivers which are not upstream are accepted directly if they fall into the first two categories.

How does the process work?

• First step for every SRU is to have a bug associated.

• The patch or patches must contain the link to the Launchpad bug and contain a Signed-off-by line from the submitter. Please refer to https://wiki.ubuntu.com/Kernel/Dev/StablePatchFormat for detailed information regarding Ubuntu Kernel SRU patch formatting.

• The beginning of the description area of the bug needs to have a SRU justification which should look like this example:

      SRU Justification:
  
      Impact: <a short description about the symptoms and the impact of the bug>
      Fix: <how was this fixed, where did the fix come from>
      Testcase: <how can the fix be tested>

• If the fix for a problem meets the requirements for SRU and has been tested to successfully solve the bug, then the next step depends on whether the fix is serious enough to be directly applied to an Ubuntu kernel series and/or whether it should go in via upstream stable (as long as that is appropriate for upstream stable).

  • For fixes for serious issues, the patch should be sent the the kernel-team mailing list in parallel to being submitted upstream. SRU patches submitted for inclusion into an Ubuntu kernel require ACK's from at least two senior Ubuntu kernel-team members before being applied to an Ubuntu kernel tree. Again, even when going into an Ubuntu kernel tree on an accelerated path, the patch should also be submitted upstream. Ubuntu Kernel SRU patch submission format is loosely as follows:

        To: kernel-team@lists.ubuntu.com
        Subject: [<series>] SRU: <bug/patch title>
    
        <SRU justification copied from the bug>
    
        <patch inlined or pull request>

  • For all other patches which do not need an accelerated path into an Ubuntu kernel, it is advised to push the fix upstream when appropriate, ie. the problem exists upstream, and CC'ing stable@kernel.org during the process. As soon as the patch is accepted upstream/upstream-stable, it will naturally find it's way back down into our Ubuntu kernel when we pull upstream/upstream-stable updates. This ensures patches are getting vetted and applied upstream and reduces overall maintenance costs for the Ubuntu Kernel Team.

How will updates be provided in the archive?

• Security updates will be uploaded directly into -security without other changes. This just requires a temporary GIT fork which will be immediately merged back into the main branch for that stable release.
• Normal updates will be provided as pre-releases through the kernel-ppa users PPA. At certain points those get made into proposed releases which are uploaded to the proposed pocket. Then again they have to get verified to fix the problems and not to cause regressions.