From 94753da021d0849f4858e2c2cb98b3276842b665 Mon Sep 17 00:00:00 2001
From: Eduardo Otubo <otubo@redhat.com>
Date: Mon, 24 Aug 2020 15:34:24 +0200
Subject: [PATCH 1/5] DHCP sandboxing failing on noexec mounted /var/tmp (#521)

RH-Author: Eduardo Terrell Ferrari Otubo (eterrell)
RH-MergeRequest: 1: DHCP sandboxing failing on noexec mounted /var/tmp (#521)
RH-Commit: [1/1] 4971d742aa1de27dff61b07ef9d6d478c0889ded (eterrell/cloud-init)
RH-Bugzilla: 1879989

commit db86753f81af73826158c9522f2521f210300e2b
Author: Eduardo Otubo <otubo@redhat.com>
Date:   Mon Aug 24 15:34:24 2020 +0200

    DHCP sandboxing failing on noexec mounted /var/tmp (#521)

    * DHCP sandboxing failing on noexec mounted /var/tmp

    If /var/tmp is mounted with noexec option the DHCP sandboxing will fail
    with Permission Denied. This patch simply avoids this error by checking
    the exec permission updating the dhcp path in negative case.

    rhbz: https://bugzilla.redhat.com/show_bug.cgi?id=1879989

    Signed-off-by: Eduardo Otubo <otubo@redhat.com>

    * Replacing with os.* calls

    * Adding test and removing isfile() useless call.

    Co-authored-by: Rick Harding <rharding@mitechie.com>

Signed-off-by: Eduardo Otubo <otubo@redhat.com>
---
 cloudinit/net/dhcp.py            |  6 ++++++
 cloudinit/net/tests/test_dhcp.py | 46 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/cloudinit/net/dhcp.py b/cloudinit/net/dhcp.py
index c033cc8..841e72e 100644
--- a/cloudinit/net/dhcp.py
+++ b/cloudinit/net/dhcp.py
@@ -215,6 +215,12 @@ def dhcp_discovery(dhclient_cmd_path, interface, cleandir):
     pid_file = os.path.join(cleandir, 'dhclient.pid')
     lease_file = os.path.join(cleandir, 'dhcp.leases')
 
+    # In some cases files in /var/tmp may not be executable, launching dhclient
+    # from there will certainly raise 'Permission denied' error. Try launching
+    # the original dhclient instead.
+    if not os.access(sandbox_dhclient_cmd, os.X_OK):
+        sandbox_dhclient_cmd = dhclient_cmd_path
+
     # ISC dhclient needs the interface up to send initial discovery packets.
     # Generally dhclient relies on dhclient-script PREINIT action to bring the
     # link up before attempting discovery. Since we are using -sf /bin/true,
diff --git a/cloudinit/net/tests/test_dhcp.py b/cloudinit/net/tests/test_dhcp.py
index c3fa1e0..08e2cfb 100644
--- a/cloudinit/net/tests/test_dhcp.py
+++ b/cloudinit/net/tests/test_dhcp.py
@@ -406,6 +406,52 @@ class TestDHCPDiscoveryClean(CiTestCase):
                  'eth9', '-sf', '/bin/true'], capture=True)])
         m_kill.assert_has_calls([mock.call(my_pid, signal.SIGKILL)])
 
+    @mock.patch('cloudinit.net.dhcp.util.get_proc_ppid')
+    @mock.patch('cloudinit.net.dhcp.os.kill')
+    @mock.patch('cloudinit.net.dhcp.subp.subp')
+    def test_dhcp_discovery_outside_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.
+        """
+        m_subp.return_value = ('', '')
+        tmpdir = self.tmp_dir()
+        dhclient_script = os.path.join(tmpdir, 'dhclient.orig')
+        script_content = '#!/bin/bash\necho fake-dhclient'
+        write_file(dhclient_script, script_content, mode=0o755)
+        lease_content = dedent("""
+            lease {
+              interface "eth9";
+              fixed-address 192.168.2.74;
+              option subnet-mask 255.255.255.0;
+              option routers 192.168.2.1;
+            }
+        """)
+        lease_file = os.path.join(tmpdir, 'dhcp.leases')
+        write_file(lease_file, lease_content)
+        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
+
+        with mock.patch('os.access', return_value=False):
+            self.assertCountEqual(
+                [{'interface': 'eth9', 'fixed-address': '192.168.2.74',
+                  'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1'}],
+                dhcp_discovery(dhclient_script, 'eth9', tmpdir))
+        # dhclient script got copied
+        with open(os.path.join(tmpdir, 'dhclient.orig')) as stream:
+            self.assertEqual(script_content, stream.read())
+        # Interface was brought up before dhclient called from sandbox
+        m_subp.assert_has_calls([
+            mock.call(
+                ['ip', 'link', 'set', 'dev', 'eth9', 'up'], capture=True),
+            mock.call(
+                [os.path.join(tmpdir, 'dhclient.orig'), '-1', '-v', '-lf',
+                 lease_file, '-pf', os.path.join(tmpdir, 'dhclient.pid'),
+                 'eth9', '-sf', '/bin/true'], capture=True)])
+        m_kill.assert_has_calls([mock.call(my_pid, signal.SIGKILL)])
+
 
 class TestSystemdParseLeases(CiTestCase):
 
-- 
1.8.3.1