From df891f0593d234e01f27d7c0376d9702e178ecfb Mon Sep 17 00:00:00 2001
From: Slawek Kaplonski <skaplons@redhat.com>
Date: Tue, 31 Aug 2021 15:43:11 +0200
Subject: [PATCH] Remove dhcp_extra_opt value after first newline character

Passing newline to the dnsmasq may cause security issues, especially
that in case of Neutron that dhcp options' values are controlled by
cloud users.
This patch removes everything what is after first newline character
in the dhcp_extra_opt's values before passing them to dnsmasq.

Closes-Bug: #1939733
Change-Id: Ifeaf258f0b5ea86f25620ac4116d618980a7272e
---
 neutron/agent/linux/dhcp.py                                | 7 ++++---
 neutron/tests/unit/agent/linux/test_dhcp.py                | 7 ++++++-
 ...wline-chars-in-dhcp-extra-options-bf86d30371556d63.yaml | 6 ++++++
 3 files changed, 16 insertions(+), 4 deletions(-)
 create mode 100644 releasenotes/notes/fix-newline-chars-in-dhcp-extra-options-bf86d30371556d63.yaml

diff --git a/neutron/agent/linux/dhcp.py b/neutron/agent/linux/dhcp.py
index dd8f3175252..8e247adb240 100644
--- a/neutron/agent/linux/dhcp.py
+++ b/neutron/agent/linux/dhcp.py
@@ -1322,10 +1322,11 @@ class Dnsmasq(DhcpLocalProcess):
         elif not option.isdigit():
             option = 'option:%s' % option
         if extra_tag:
-            tags = ('tag:' + tag, extra_tag[:-1], '%s' % option)
+            tags = ['tag:' + tag, extra_tag[:-1], '%s' % option]
         else:
-            tags = ('tag:' + tag, '%s' % option)
-        return ','.join(tags + args)
+            tags = ['tag:' + tag, '%s' % option]
+
+        return ','.join(tags + [v.split("\n", 1)[0] for v in args])
 
     @staticmethod
     def _convert_to_literal_addrs(ip_version, ips):
diff --git a/neutron/tests/unit/agent/linux/test_dhcp.py b/neutron/tests/unit/agent/linux/test_dhcp.py
index aa50ff89732..4a9cfaf5072 100644
--- a/neutron/tests/unit/agent/linux/test_dhcp.py
+++ b/neutron/tests/unit/agent/linux/test_dhcp.py
@@ -230,6 +230,9 @@ class FakeV6PortExtraOpt(object):
         self.extra_dhcp_opts = [
             DhcpOpt(opt_name='dns-server',
                     opt_value='ffea:3ba5:a17a:4ba3::100',
+                    ip_version=constants.IP_VERSION_6),
+            DhcpOpt(opt_name='malicious-option',
+                    opt_value='aaa\nbbb.ccc\n',
                     ip_version=constants.IP_VERSION_6)]
 
 
@@ -2910,7 +2913,9 @@ class TestDnsmasq(TestBase):
         exp_opt_data = ('tag:subnet-eeeeeeee-eeee-eeee-eeee-eeeeeeeeeeee,'
                         'option6:domain-search,openstacklocal\n'
                         'tag:port-hhhhhhhh-hhhh-hhhh-hhhh-hhhhhhhhhhhh,'
-                        'option6:dns-server,ffea:3ba5:a17a:4ba3::100').lstrip()
+                        'option6:dns-server,ffea:3ba5:a17a:4ba3::100\n'
+                        'tag:port-hhhhhhhh-hhhh-hhhh-hhhh-hhhhhhhhhhhh,'
+                        'option6:malicious-option,aaa').lstrip()
         dm = self._get_dnsmasq(FakeV6NetworkStatelessDHCP())
         dm._output_hosts_file()
         dm._output_opts_file()
diff --git a/releasenotes/notes/fix-newline-chars-in-dhcp-extra-options-bf86d30371556d63.yaml b/releasenotes/notes/fix-newline-chars-in-dhcp-extra-options-bf86d30371556d63.yaml
new file mode 100644
index 00000000000..d2a8c2f68bb
--- /dev/null
+++ b/releasenotes/notes/fix-newline-chars-in-dhcp-extra-options-bf86d30371556d63.yaml
@@ -0,0 +1,6 @@
+---
+security:
+  - |
+    Fix `bug 1939733 <https://bugs.launchpad.net/neutron/+bug/1939733>`_ by
+    dropping from the dhcp extra option values everything what is after first
+    newline (``\n``) character before passing them to the dnsmasq.