Fix exit of subprocess in case it was terminated by signal

If child process of rootwrap is terminated by signal, exit code should
be 128 + N, where N is number of signal. According [1]
subprocess.Popen.returncode returns -N. sys.exit interprets negative
signed byte as unsigned thus original exit code is 256 - N instead of
128 + N.

[1]
https://docs.python.org/2/library/subprocess.html#subprocess.Popen.returncode

Change-Id: I43b4c959a98f8f620466c77de4cd5b724b09e5a8
Closes-Bug: #1364822

oslo/rootwrap/cmd.py

@@ -44,6 +44,7 @@ RC_UNAUTHORIZED = 99
 RC_NOCOMMAND = 98
 RC_BADCONFIG = 97
 RC_NOEXECFOUND = 96
+SIGNAL_BASE = 128
 
 
 def _exit_error(execname, message, errorcode, log=True):
@@ -106,8 +107,11 @@ def run_one_command(execname, config, filters, userargs):
             stdin=sys.stdin,
             stdout=sys.stdout,
             stderr=sys.stderr)
-        obj.wait()
-        sys.exit(obj.returncode)
+        returncode = obj.wait()
+        # Fix returncode of Popen
+        if returncode < 0:
+            returncode = SIGNAL_BASE - returncode
+        sys.exit(returncode)
 
     except wrapper.FilterMatchNotExecutable as exc:
         msg = ("Executable not found: %s (filter match = %s)"

tests/test_rootwrap.py

@@ -23,6 +23,7 @@ import mock
 from six import moves
 import testtools
 
+from oslo.rootwrap import cmd
 from oslo.rootwrap import filters
 from oslo.rootwrap import wrapper
 
@@ -567,3 +568,18 @@ class PathFilterTestCase(testtools.TestCase):
                     os.path.realpath(self.TRAVERSAL_SYMLINK_WITHIN_DIR)]
 
         self.assertEqual(expected, self.f.get_command(args))
+
+
+class RunOneCommandTestCase(testtools.TestCase):
+    def _test_returncode_helper(self, returncode, expected):
+        with mock.patch.object(wrapper, 'start_subprocess') as mock_start:
+            with mock.patch('sys.exit') as mock_exit:
+                mock_start.return_value.wait.return_value = returncode
+                cmd.run_one_command(None, mock.Mock(), None, None)
+        mock_exit.assert_called_once_with(expected)
+
+    def test_positive_returncode(self):
+        self._test_returncode_helper(1, 1)
+
+    def test_negative_returncode(self):
+        self._test_returncode_helper(-1, 129)