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[Openstack-security] [Bug 1739646] Re: Instance type with disk set to 0 can cause DoS

Oh, thanks, I guess if there are stable backports coming after all we
can keep it as a class A report. Once there are backports linked from
Gerrit I'll whip up an impact description and request a CVE assignment
for this.

** Information type changed from Public to Public Security

** Changed in: ossa
       Status: Won't Fix => Incomplete

** Tags removed: security

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  Instance type with disk set to 0 can cause DoS

Status in OpenStack Compute (nova):
Status in OpenStack Compute (nova) ocata series:
Status in OpenStack Compute (nova) pike series:
Status in OpenStack Compute (nova) queens series:
Status in OpenStack Security Advisory:

Bug description:
  In OpenStack at the moment, there is the ability to create instance
  types with disk size 0.  The API documentation states the following:

  "The size of the root disk that will be created in GiB. If 0 the root
  disk will be set to exactly the size of the image used to deploy the
  instance. However, in this case filter scheduler cannot select the
  compute host based on the virtual image size. Therefore, 0 should only
  be used for volume booted instances or for testing purposes."

  In a cloud environment where a deployer wants to offer boot-from-
  volume instances, those instance types will be there.  However, this
  means that a user can upload an image of 4TB and boot small instances
  where each one will have 4TB of storage, potentially exhausting the
  disks local storage (or Ceph cluster if using Ceph for ephemeral

  I'm not sure if this is a security issue or it should be published as
  an advisory, but I believe there should be an option to disable the
  feature of booting an instance with the exact size of the image used
  so deployers have the ability/choice to provide boot-from-volume
  instance types.

  I can confirm this in our environment that if a customer creates an
  instance with 200GB of ephemeral disk space, they can take an image of
  it, then create an instance with that image on an instance type that
  has no ephemeral disk space and get 200GB of disk.

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