cloud-init

namespace collision on url kernel arg results in downloading iso multiple times

Bug #1937319 reported by Dan Bungert on 2021-07-22

This bug affects 2 people

Affects		Status	Importance	Assigned to	Milestone
	cloud-init	Fix Released	Medium	Alberto Contreras
	casper (Ubuntu)	Fix Released	Undecided	Unassigned

Bug Description

As listed at https://discourse.ubuntu.com/t/netbooting-the-live-server-installer/14510/135

When attempting a netboot, we can end up in a situation where cloud-init downloads a full iso, only to decide that the first few bytes aren't the expected header and to ignore it.

I suggest an enhancement where a small amount of data is downloaded at first, we check this data for the required #cloud-config, and then use that info to decide to continue to download the file or not.

Related branches

~mwhudson/casper:additional-iso-url

Merged into casper:main at revision 0014d2f7c824ec8847c5e0e5e5dbb83c9dd25259

Dan Bungert (community): Approve on 2022-06-02

Ubuntu Installer Team: Pending requested 2022-06-02

Revision history for this message

James Falcon (falcojr) wrote on 2021-07-23:

How is cloud-init getting pointed to an iso? Is there a way this can happen that isn't the result of a simple misconfiguration?

Changed in cloud-init:
status:	New → Incomplete

Revision history for this message

Dan Bungert (dbungert) wrote on 2021-07-23:

It's valid for netboot to do something like this:
APPEND root=/dev/ram0 ramdisk_size=1500000 ip=dhcp url=http://releases.ubuntu.com/focal/ubuntu-20.04.1-live-server-amd64.iso
See the top post of that discourse for more details:
https://discourse.ubuntu.com/t/netbooting-the-live-server-installer/14510

So the url argument is rational for netboot, but there is a namespace collision here.

It's my hope that we fix this in multiple ways
1) add a new argument for netboot, one that isn't the generic 'url=', much like how cloud-init can accept 'cloud-config-url' instead of 'url'
2) Address the issue here, so that existing users don't download isos more times than intended until they learn about the fix in #1

What do you think?

Changed in cloud-init:
status:	Incomplete → New

Revision history for this message

Dan Bungert (dbungert) wrote on 2021-07-23:

See also: https://discourse.ubuntu.com/t/ubuntu-20-04-installer-downloads-iso-more-than-once/21697/3

Revision history for this message

James Falcon (falcojr) wrote on 2021-07-23:

Thanks for the context. Yes, I think your proposal makes sense.

Changed in cloud-init:
status:	New → Triaged
importance:	Undecided → Medium

Dan Bungert (dbungert) on 2021-07-23

summary:

- cloud-init can attempt to download an iso from kernel arg url
+ namespace collision on url kernel arg results in downloading iso
+ multiple times

Revision history for this message

Michael Hudson-Doyle (mwhudson) wrote on 2021-07-30:

I had a look at the code that does this download and the structure of the APIs used looks to make this kind of sniffing a bit awkward :( Nothing impossible of course but it's not going to be completely trivial either.

Revision history for this message

Launchpad Janitor (janitor) wrote on 2022-04-27:

Status changed to 'Confirmed' because the bug affects multiple users.

Changed in casper (Ubuntu):
status:	New → Confirmed

Dan Bungert (dbungert) on 2022-06-02

Changed in casper (Ubuntu):
status:	Confirmed → In Progress

Revision history for this message

Launchpad Janitor (janitor) wrote on 2022-06-03:

This bug was fixed in the package casper - 1.472

---------------
casper (1.472) kinetic; urgency=medium

* Support iso-url= on the kernel command line as a synonym for url=, to
help avoid the conflict with cloud-init over that argument. (LP: #1937319)

-- Michael Hudson-Doyle <email address hidden> Fri, 03 Jun 2022 11:25:33 +1200

Changed in casper (Ubuntu):
status:	In Progress → Fix Released

Revision history for this message

Alberto Contreras (aciba) wrote on 2022-07-20:

PR to avoid downloading urls that does not contain cloud-configs: https://github.com/canonical/cloud-init/pull/1606

Chad Smith (chad.smith) on 2022-08-04

Changed in cloud-init:
status:	Triaged → In Progress
assignee:	nobody → Alberto Contreras (aciba)

Revision history for this message

Chad Smith (chad.smith) wrote on 2022-08-05:

Upsream commit landed with a fix for this in cloud-init https://github.com/canonical/cloud-init/commit/8e26b2f8a9ce8c1186a6e5f2e9bd90a984fde52a

Changed in cloud-init:
status:	In Progress → Fix Committed

Revision history for this message

Brett Holman (holmanb) wrote on 2022-08-19: Fixed in cloud-init version 22.3.

#10

This bug is believed to be fixed in cloud-init in version 22.3. If this is still a problem for you, please make a comment and set the state back to New

Thank you.