Set owner of drive-audit recon cache to swift user

Fixies this problem:
* swift-drive-audit needs to be run by root, because only root have
  "umount" permission
* swift-object servers typically runs as user swift
* if swift-drive-audit is run by root, /var/cache/swift/drive.recon is
  owned by root, with 0o600
* recon middleware (inside swift-object-server) can't read this cache
  file: swift-object: Error reading recon cache file

This patch adds "user" option to drive-audit config file. Recon cache
is chowned to this user.
(cherry picked from commit 9847796)

Change-Id: Ibf20543ee690b7c5a37fabd1540fd5c0c7b638c9

bin/swift-drive-audit

@@ -208,7 +208,8 @@ if __name__ == '__main__':
                     total_errors += count
     recon_file = recon_cache_path + "/drive.recon"
     dump_recon_cache(recon_errors, recon_file, logger)
-    dump_recon_cache({'drive_audit_errors': total_errors}, recon_file, logger)
+    dump_recon_cache({'drive_audit_errors': total_errors}, recon_file, logger,
+                     set_owner=conf.get("user", "swift"))
 
     if unmounts == 0:
         logger.info("No drives were unmounted")

doc/source/admin_guide.rst

@@ -264,6 +264,8 @@ settings:
 ==================  ==============  ===========================================
 Option              Default         Description
 ------------------  --------------  -------------------------------------------
+user                swift           Drop privileges to this user for non-root
+                                    tasks
 log_facility        LOG_LOCAL0      Syslog log facility
 log_level           INFO            Log level
 device_dir          /srv/node       Directory devices are mounted under

etc/drive-audit.conf-sample

@@ -1,4 +1,5 @@
 [drive-audit]
+# user = swift
 # device_dir = /srv/node
 #
 # You can specify default log routing here if you want:

swift/common/utils.py

@@ -3037,13 +3037,15 @@ def put_recon_cache_entry(cache_entry, key, item):
         cache_entry[key] = item
 
 
-def dump_recon_cache(cache_dict, cache_file, logger, lock_timeout=2):
+def dump_recon_cache(cache_dict, cache_file, logger, lock_timeout=2,
+                     set_owner=None):
     """Update recon cache values
 
     :param cache_dict: Dictionary of cache key/value pairs to write out
     :param cache_file: cache file to update
     :param logger: the logger to use to log an encountered error
     :param lock_timeout: timeout (in seconds)
+    :param set_owner: Set owner of recon cache file
     """
     try:
         with lock_file(cache_file, lock_timeout, unlink=False) as cf:
@@ -3062,6 +3064,8 @@ def dump_recon_cache(cache_dict, cache_file, logger, lock_timeout=2):
                 with NamedTemporaryFile(dir=os.path.dirname(cache_file),
                                         delete=False) as tf:
                     tf.write(json.dumps(cache_entry) + '\n')
+                if set_owner:
+                    os.chown(tf.name, pwd.getpwnam(set_owner).pw_uid, -1)
                 renamer(tf.name, cache_file, fsync=False)
             finally:
                 if tf is not None:

test/unit/common/test_utils.py

@@ -1377,6 +1377,28 @@ class TestUtils(unittest.TestCase):
         finally:
             rmtree(testdir_base)
 
+    def test_dump_recon_cache_set_owner(self):
+        testdir_base = mkdtemp()
+        testcache_file = os.path.join(testdir_base, 'cache.recon')
+        logger = utils.get_logger(None, 'server', log_route='server')
+        try:
+            submit_dict = {'key1': {'value1': 1, 'value2': 2}}
+
+            _ret = lambda: None
+            _ret.pw_uid = 100
+            _mock_getpwnam = MagicMock(return_value=_ret)
+            _mock_chown = mock.Mock()
+
+            with patch('os.chown', _mock_chown), \
+                    patch('pwd.getpwnam', _mock_getpwnam):
+                utils.dump_recon_cache(submit_dict, testcache_file,
+                                       logger, set_owner="swift")
+
+            _mock_getpwnam.assert_called_once_with("swift")
+            self.assertEqual(_mock_chown.call_args[0][1], 100)
+        finally:
+            rmtree(testdir_base)
+
     def test_dump_recon_cache_permission_denied(self):
         testdir_base = mkdtemp()
         testcache_file = os.path.join(testdir_base, 'cache.recon')