[nova][glance] Granting image member access for snapshots (bug 1675791)

Matt Riedemann mriedemos at gmail.com
Tue Jan 15 00:04:06 UTC 2019

I have a fix proposed for a pretty old bug (1675791 [1]). This 
originally came up because of a scenario where an admin shelves a server 
and then the owner of the shelved server cannot unshelve it since they 
do not have access to the shelve snapshot image.

The same is true for normal snapshot and backup operations though, see 
this proposed spec for Stein [2].

It also came up during the cross-cell resize spec review [3] since that 
solution depends on snapshot to get the root disk from one cell to another.

In a nutshell, when creating a snapshot now, the compute API will check 
if the project creating the snapshot is the same as the project owner of 
the server. If not, the image is created with visibility=shared and the 
project owner of the instance is granted member access to the image, 
which allows them to GET the image directly via the ID, but not list it 
by default (the tenant user has to accept the pending membership for 
that). I have tested this out in devstack today and everything seems to 
work well.

I am posting this to (a) raise awareness of the bug and proposed fix 
since it is sort of a behavior change in the 
createImage/createBackup/shelve APIs and (b) to make sure the glance 
team is aware and acknowledges this is an OK thing to do, i.e. are there 
any kind of unforeseen side effects of automatically granting image 
membership like this (I would think not since the owner of the instance 
has access to the root disk of the server anyway - it is their data).

Also note that some really crusty legacy code in most of the in-tree 
virt drivers had to be removed (some virt drivers would change the image 
visibility back to private during the actual data upload to glance) 
which could mean out of tree drivers have the same issue.

[1] https://bugs.launchpad.net/nova/+bug/1675791
[2] https://review.openstack.org/#/c/616843/




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