[Bug 1611603] [NEW] fails to start when confined in a snap

[Paul Collins]

Public bug reported:

I attempted to package a simple WSGI app in an Ubuntu snap with
gunicorn, and ran into a problem with gunicorn vs. the Snap security
policy.

The policy forbids calling chown at all, whereas the
gunicorn.worker.WorkerTemp class relies on the default and historically
unproblematic behaviour of silently succeeding when the UID/GID are the
same as the calling process's.

I've attached a patch that attempts to short-circuit chown when it would
be a no-op, which is the case when gunicorn is run as root in a snap,
and this patch lets my app work when confined.

snaps also do not currently allow setuid, etc., and so there's no sense
in trying to create a gunicorn-using snap that starts as root and then
drops privileges.  For more information on the snap security policy,
please visit: https://developer.ubuntu.com/en/snappy/guides/security/

** Affects: gunicorn (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: canonical-is

** Patch added: "skip chown when it would be a no-op"
   https://bugs.launchpad.net/bugs/1611603/+attachment/4717942/+files/gunicorn.chown.patch

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https://bugs.launchpad.net/bugs/1611603

Title:
  fails to start when confined in a snap

Status in gunicorn package in Ubuntu:
  New

Bug description:
  I attempted to package a simple WSGI app in an Ubuntu snap with
  gunicorn, and ran into a problem with gunicorn vs. the Snap security
  policy.

  The policy forbids calling chown at all, whereas the
  gunicorn.worker.WorkerTemp class relies on the default and
  historically unproblematic behaviour of silently succeeding when the
  UID/GID are the same as the calling process's.

  I've attached a patch that attempts to short-circuit chown when it
  would be a no-op, which is the case when gunicorn is run as root in a
  snap, and this patch lets my app work when confined.

  snaps also do not currently allow setuid, etc., and so there's no
  sense in trying to create a gunicorn-using snap that starts as root
  and then drops privileges.  For more information on the snap security
  policy, please visit:
  https://developer.ubuntu.com/en/snappy/guides/security/

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