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, 12 insertions, 3 deletions

diff --git a/cloudinit/net/tests/test_dhcp.py b/cloudinit/net/tests/test_dhcp.py
index cd3e7328..79e8842f 100644
--- a/cloudinit/net/tests/test_dhcp.py
+++ b/cloudinit/net/tests/test_dhcp.py
@@ -145,16 +145,20 @@ class TestDHCPDiscoveryClean(CiTestCase):
               'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1'}],
             dhcp_discovery(dhclient_script, 'eth9', tmpdir))
         self.assertIn(
-            "pid file contains non-integer content ''", self.logs.getvalue())
+            "dhclient(pid=, parentpid=unknown) failed "
+            "to daemonize after 10.0 seconds",
+            self.logs.getvalue())
         m_kill.assert_not_called()
 
+    @mock.patch('cloudinit.net.dhcp.util.get_proc_ppid')
     @mock.patch('cloudinit.net.dhcp.os.kill')
     @mock.patch('cloudinit.net.dhcp.util.wait_for_files')
     @mock.patch('cloudinit.net.dhcp.util.subp')
     def test_dhcp_discovery_run_in_sandbox_waits_on_lease_and_pid(self,
                                                                   m_subp,
                                                                   m_wait,
-                                                                  m_kill):
+                                                                  m_kill,
+                                                                  m_getppid):
         """dhcp_discovery waits for the presence of pidfile and dhcp.leases."""
         tmpdir = self.tmp_dir()
         dhclient_script = os.path.join(tmpdir, 'dhclient.orig')
@@ -164,6 +168,7 @@ class TestDHCPDiscoveryClean(CiTestCase):
         pidfile = self.tmp_path('dhclient.pid', tmpdir)
         leasefile = self.tmp_path('dhcp.leases', tmpdir)
         m_wait.return_value = [pidfile]  # Return the missing pidfile wait for
+        m_getppid.return_value = 1  # Indicate that dhclient has daemonized
         self.assertEqual([], dhcp_discovery(dhclient_script, 'eth9', tmpdir))
         self.assertEqual(
             mock.call([pidfile, leasefile], maxwait=5, naplen=0.01),
@@ -173,9 +178,10 @@ class TestDHCPDiscoveryClean(CiTestCase):
             self.logs.getvalue())
         m_kill.assert_not_called()
 
+    @mock.patch('cloudinit.net.dhcp.util.get_proc_ppid')
     @mock.patch('cloudinit.net.dhcp.os.kill')
     @mock.patch('cloudinit.net.dhcp.util.subp')
-    def test_dhcp_discovery_run_in_sandbox(self, m_subp, m_kill):
+    def test_dhcp_discovery_run_in_sandbox(self, m_subp, m_kill, m_getppid):
         """dhcp_discovery brings up the interface and runs dhclient.
 
         It also returns the parsed dhcp.leases file generated in the sandbox.
@@ -197,6 +203,7 @@ class TestDHCPDiscoveryClean(CiTestCase):
         pid_file = os.path.join(tmpdir, 'dhclient.pid')
         my_pid = 1
         write_file(pid_file, "%d\n" % my_pid)
+        m_getppid.return_value = 1  # Indicate that dhclient has daemonized
 
         self.assertItemsEqual(
             [{'interface': 'eth9', 'fixed-address': '192.168.2.74',
@@ -355,3 +362,5 @@ class TestEphemeralDhcpNoNetworkSetup(HttprettyTestCase):
             self.assertEqual(fake_lease, lease)
         # Ensure that dhcp discovery occurs
         m_dhcp.called_once_with()
+
+# vi: ts=4 expandtab