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?

There are several categories of updates, in addition to normal security updates:

• Critical bug fixes. These are categorized as non-security issues relating to bugs that affect a large range of users. These are bugs that keep users from reliably using their systems, or prevent booting at all. These patches must pass through rigorous testing by Canonical/Ubuntu and the community at large.

• Supported vendor patches. These are patches generally related to hardware support. If they are very specific to a piece of hardware, the nature of the patch makes regression on other hardware unlikely or impossible, and we have the hardware available for thorough testing, then it can be part of an SRU. Otherwise they need to be maintained in a separate repository/pocket/PPA specific for that vendor or, if appropriate, in linux-backports-modules, and thus need to be maintained separately in the future. This also depends on whether a change relates to a LTS or a non-LTS release. While small changes to add drivers can be considered throughout the lifetime of an LTS, this will be limited to the point in time the next kernel hits beta status.

Other changes are generally avoided on stable kernels, since the regression potential is so exceptionally high.

All non-security changes need to follow the standard SRU procedure in terms of having a bug associated with them, which is fixed in the development release and signed off by ubuntu-sru or canonical-qa, and the changelog needs to include the bug number.

How long will updates be allowed for a release

This answer is directed at non-LTS releases. For normal 18-month releases, we will only accept updates to the kernel for 3-4 months after release. At this point we consider the in-development release to be stable enough for testing, and the primary target for fixing bugs. Plus, 3-4 months after release, most major bugs are either reported and fixed in the stable release, or deemed unfixable.

There may be a few exceptions to this, but don't count on them.

How does the process work

• First step for every SRU is to have a bug associated.
• If the fix for a problem applies to the requirements for a SRU and has also been tested to successfully solved the bug, then the next step is to send the proposed patch for SRU review to the kernel-team mailing list, where it needs to receive at least two ACKs from core kernel developers. The review should include a generic header which describes the impact, and the fix, and how the issue can be tested. The same information should go into the description of the launchpad bug, so the stable release team can quickly find it.

How will updates be provided in the archive

• Urgent 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.
• Less urgent security updates and non-security patches will be uploaded to -proposed and then just follow the normal SRU QA procedure (testing, confirming bugs, etc). After verification, these kernels are copied verbatim to -security, and the USN is issued. This avoids maintaining two GIT trees for stable releases while still keeping the testing period.
• Non-security updates which change the ABI should be either avoided at all, or be combined with security updates which require ABI change anyway.