builtins.PermissionError: [Errno 1] Operation not permitted: '/var/lib/maas/.maas-proxy.conf.wwu2aw6z.tmp'

[Felipe Reyes]

It was found an environment where there were about ~50 GB of files /var/lib/maas/.maas-proxy.conf.* , this was happening because /var/lib/maas/.maas-proxy.conf was owner by postgres:postgres , so maas was trying to apply the same permissions to the temporary file which failed since the process maas-regiond is running under the 'maas' user.

2020-06-16 15:34:46 maasserver.region_controller: [critical] Failed configuring proxy.
        Traceback (most recent call last):
          File "/usr/lib/python3.6/threading.py", line 864, in run
            self._target(*self._args, **self._kwargs)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 850, in worker
            return target()
          File "/usr/lib/python3/dist-packages/twisted/_threads/_threadworker.py", line 46, in work
            task()
          File "/usr/lib/python3/dist-packages/twisted/_threads/_team.py", line 190, in doWork
            task()
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 250, in inContext
            result = inContext.theWork()
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 266, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 122, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 85, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 885, in callInContext
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 217, in wrapper
            result = func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 737, in call_within_transaction
            return func_outside_txn(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 540, in retrier
            return func(*args, **kwargs)
          File "/usr/lib/python3.6/contextlib.py", line 52, in inner
            return func(*args, **kwds)
          File "/usr/lib/python3/dist-packages/maasserver/proxyconfig.py", line 60, in _write_config
            write_config(cidrs, **kwargs)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 217, in wrapper
            result = func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/provisioningserver/proxy/config.py", line 85, in write_config
            atomic_write(content, target_path, overwrite=True, mode=0o644)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/fs.py", line 151, in atomic_write
            chown(temp_file, prev_stats.st_uid, prev_stats.st_gid)
        builtins.PermissionError: [Errno 1] Operation not permitted: '/var/lib/maas/.maas-proxy.conf.wwu2aw6z.tmp'

[Test case]

1. Install MAAS from deb packages (tested with 2.7 and 2.8).
2. sudo chown postgres:postgres /var/lib/maas/maas-proxy.conf
3. echo "# This shouldn't be here" | sudo tee -a /var/lib/maas/maas-proxy.conf
4. sudo systemctl restart maas-regiond
5. ls /var/lib/maas/.maas-proxy.*

Expected result:

The failure of chown() gets logged and the temporary file removed.

Actual result:

chown()'s PermissionError is not handled and leaving the temporary file behind.