I've marked the OSSA task as "won't fix" to indicate this issue isn't one for which the project vulnerability management team would publish a coordinated security advisory, as the conditions by which it is triggered do not seem to be under direct control of a malicious actor but rather one of volume and statistical happenstance. This does definitely still sound like an annoying bug, however, and one which the Nova developers will hopefully address in a timely manner.
** Changed in: ossa Status: Incomplete => Won't Fix -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1350766 Title: Race condition: compute intermittently corrupts base images on download from glance Status in OpenStack Compute (Nova): In Progress Status in OpenStack Security Advisories: Won't Fix Bug description: Under certain conditions, which I happen to meet often on my Icehouse single node setup, uploaded images or snapshots fail to boot. See also https://ask.openstack.org/en/question/42804/icehouse-how-to-boot-a -snapshot-from-a-running-instance/ Reason: When first instantiating a QCOW2 image, it's (1) downloaded as QCOW2 to /var/lib/nova/instances/_base/IMAGEID.part (2) converted to RAW format base /var/lib/nova/instances/_base/IMAGEID.converted using qemu-img The step (1) is performed in nova/image/glance.py, GlanceImageService.download using buffered IO, which does not guarantee the resulting data to be written to disk on file close. Consequently, the source image file may not be written completely when qemu-img sub-process starts reading in step (2). Whether the result is good or bad depends on speed of download, file size, and how quickly qemu-image can digest its input. Proposed fix: enforce fsync on output File object before returning from download. Patch attached. Security considerations: * Due to the race between resources shared between users and tenants (compute node network and filesystem IO) a failure can be triggered across tenants, implying the risk of DoS. * To make things worse -- with the default setting of not cleaning the image cache -- any corrupted image will remain in cache until replaced with fresh upload using a new image ID. Affected snapshots remain unusable forever, until ex- and re-imported manually under better conditions. * Base image corruptions here are not detected and cannot be caught. Theoretically (a bit esoteric, quite unlikely, but not impossible), an attacker might modulate resource usage to precisely create an incompletely written image, that boots and runs, but has access control information stripped. To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1350766/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : yahoo-eng-team@lists.launchpad.net Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp