[Bug 1379080] [NEW] update-grub-legacy-ec2 fails to detect xen kernel

[evan2645]

Public bug reported:

The update-grub-legacy-ec2 script (which ships with grub-legacy-ec2,
which is presumably included under cloud-init umbrella) includes a check
to determine whether a kernel is Xen-capable or not. It uses this check
in a feature designed to ignore non-Xen kernels on Xen guests,
presumably as a safety mechanism. The way in which the check is executed
is flawed - it matches against the kernel name. This means that if you
are loading a kernel that has an 'unexpected' name, update-grub-legacy-
ec2 will ignore the new kernel, regardless of whether or not it is
actually Xen-capable. Output looks like this:

Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Ignoring non-Xen Kernel on Xen domU host: vmlinuz-3.13.0-36-custom
Found kernel: /boot/vmlinuz-3.13.0-36-generic
Updating /boot/grub/menu.lst ... done

This has been fixed on grub-legacy. Instead of matching the kernel name,
it checks the config for CONFIG_XEN=y. In addition, Linux kernels come
with CONFIG_XEN=y by default for some time now, and it is perfectly safe
to run a Xen-capable kernel on non-Xen hosts.

Steps to reproduce:
1. Compile and generate debs for custom kernel with version string not including '-generic' or '-virtual'
2. Install debs on ec2 system (ami-a94e0c99)
3. Reboot

Expected results:
System comes up with new kernel

Actual results:
System comes up with old kernel, and new kernel is not present in /boot/grub/menu.lst

Impact:
Running ami-a94e0c99, and likely many others, a user can not install a custom kernel without manually editing files. Furthermore, those writes will likely be overwritten by administrative operations in the future.

Recommendation:
Update detection logic to search for CONFIG_XEN=y in the kernel config, and remove version string detection.

Please let me know how I can help this along. I can submit a proposed
fix, but am not sure where to send it.

** Affects: cloud-init (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1379080

Title:
  update-grub-legacy-ec2 fails to detect xen kernel

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