net: Wait for dhclient to daemonize before reading lease file

cloud-init uses dhclient to fetch the DHCP lease so it can extract
DHCP options.  dhclient creates the leasefile, then writes to it;
simply waiting for the leasefile to appear creates a race between
dhclient and cloud-init. Instead, wait for dhclient to be parented by
init. At that point, we know it has written to the leasefile, so it's
safe to copy the file and kill the process.

cloud-init creates a temporary directory in which to execute dhclient,
and deletes that directory after it has killed the process. If
cloud-init abandons waiting for dhclient to daemonize, it will still
attempt to delete the temporary directory, but will not report an
exception should that attempt fail.

LP: #1794399

1 files changed, 17 insertions, 1 deletions

diff --git a/cloudinit/tests/test_temp_utils.py b/cloudinit/tests/test_temp_utils.py
index ffbb92cd..4a52ef89 100644
--- a/cloudinit/tests/test_temp_utils.py
+++ b/cloudinit/tests/test_temp_utils.py
@@ -2,8 +2,9 @@
 
 """Tests for cloudinit.temp_utils"""
 
-from cloudinit.temp_utils import mkdtemp, mkstemp
+from cloudinit.temp_utils import mkdtemp, mkstemp, tempdir
 from cloudinit.tests.helpers import CiTestCase, wrap_and_call
+import os
 
 
 class TestTempUtils(CiTestCase):
@@ -98,4 +99,19 @@ class TestTempUtils(CiTestCase):
         self.assertEqual('/fake/return/path', retval)
         self.assertEqual([{'dir': '/run/cloud-init/tmp'}], calls)
 
+    def test_tempdir_error_suppression(self):
+        """test tempdir suppresses errors during directory removal."""
+
+        with self.assertRaises(OSError):
+            with tempdir(prefix='cloud-init-dhcp-') as tdir:
+                os.rmdir(tdir)
+                # As a result, the directory is already gone,
+                # so shutil.rmtree should raise OSError
+
+        with tempdir(rmtree_ignore_errors=True,
+                     prefix='cloud-init-dhcp-') as tdir:
+            os.rmdir(tdir)
+            # Since the directory is already gone, shutil.rmtree would raise
+            # OSError, but we suppress that
+
 # vi: ts=4 expandtab