[Bug 1771928] [NEW] Disk usage leak on image import

[Alexander Kharkov]

Public bug reported:

Nova LXD driver contains a disk usage resource leak.
Each disk image import from Glance leads to O(image_size) disk space lost in /tmp.
Leak exists until nova-compute service is restarted as during restart open descriptors will be freed and disk space will reclaimed by OS.

The reason is wrong usage of mkstemp in nova/virt/lxd/driver.py _sync_glance_image_to_lxd.
The code use mkstemp to generate "random" filename to pass to glance API as destination path for downloaded image. But mkstemp also open file description to this file which is lost and never closed. As result even when this temporary file (downloaded image) is deleted file is still locked by nova-compute process.

def _sync_glance_image_to_lxd(client, context, image_ref):
...
    try:
        image_file = tempfile.mkstemp()[1]
        # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        # in code above we lost msktemp[0] of tuple which is open file handle
        # so file never be 'freed' until process finished
...
        IMAGE_API.download(context, image_ref, dest_path=image_file) 
....

** Affects: nova-lxd (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1771928

Title:
  Disk usage leak on image import

Status in nova-lxd package in Ubuntu:
  New

Bug description:
  Nova LXD driver contains a disk usage resource leak.
  Each disk image import from Glance leads to O(image_size) disk space lost in /tmp.
  Leak exists until nova-compute service is restarted as during restart open descriptors will be freed and disk space will reclaimed by OS.

  The reason is wrong usage of mkstemp in nova/virt/lxd/driver.py _sync_glance_image_to_lxd.
  The code use mkstemp to generate "random" filename to pass to glance API as destination path for downloaded image. But mkstemp also open file description to this file which is lost and never closed. As result even when this temporary file (downloaded image) is deleted file is still locked by nova-compute process.

  def _sync_glance_image_to_lxd(client, context, image_ref):
  ...
      try:
          image_file = tempfile.mkstemp()[1]
          # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          # in code above we lost msktemp[0] of tuple which is open file handle
          # so file never be 'freed' until process finished
  ...
          IMAGE_API.download(context, image_ref, dest_path=image_file) 
  ....

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