net: add rfc3442 (classless static routes) to EphemeralDHCP

The EphemeralDHCP context manager did not parse or handle
rfc3442 classless static routes which prevented reading
datasource metadata in some clouds.  This branch adds support
for extracting the field from the leases output, parsing the
format and then adding the required iproute2 ip commands to
apply (and teardown) the static routes.

LP: #1821102

1 files changed, 32 insertions, 2 deletions

diff --git a/cloudinit/net/__init__.py b/cloudinit/net/__init__.py
index e758006f..624c9b42 100644
--- a/cloudinit/net/__init__.py
+++ b/cloudinit/net/__init__.py
@@ -679,7 +679,7 @@ class EphemeralIPv4Network(object):
     """
 
     def __init__(self, interface, ip, prefix_or_mask, broadcast, router=None,
-                 connectivity_url=None):
+                 connectivity_url=None, static_routes=None):
         """Setup context manager and validate call signature.
 
         @param interface: Name of the network interface to bring up.
@@ -690,6 +690,7 @@ class EphemeralIPv4Network(object):
         @param router: Optionally the default gateway IP.
         @param connectivity_url: Optionally, a URL to verify if a usable
            connection already exists.
+        @param static_routes: Optionally a list of static routes from DHCP
         """
         if not all([interface, ip, prefix_or_mask, broadcast]):
             raise ValueError(
@@ -706,6 +707,7 @@ class EphemeralIPv4Network(object):
         self.ip = ip
         self.broadcast = broadcast
         self.router = router
+        self.static_routes = static_routes
         self.cleanup_cmds = []  # List of commands to run to cleanup state.
 
     def __enter__(self):
@@ -718,7 +720,21 @@ class EphemeralIPv4Network(object):
                 return
 
         self._bringup_device()
-        if self.router:
+
+        # rfc3442 requires us to ignore the router config *if* classless static
+        # routes are provided.
+        #
+        # https://tools.ietf.org/html/rfc3442
+        #
+        # If the DHCP server returns both a Classless Static Routes option and
+        # a Router option, the DHCP client MUST ignore the Router option.
+        #
+        # Similarly, if the DHCP server returns both a Classless Static Routes
+        # option and a Static Routes option, the DHCP client MUST ignore the
+        # Static Routes option.
+        if self.static_routes:
+            self._bringup_static_routes()
+        elif self.router:
             self._bringup_router()
 
     def __exit__(self, excp_type, excp_value, excp_traceback):
@@ -762,6 +778,20 @@ class EphemeralIPv4Network(object):
                 ['ip', '-family', 'inet', 'addr', 'del', cidr, 'dev',
                  self.interface])
 
+    def _bringup_static_routes(self):
+        # static_routes = [("169.254.169.254/32", "130.56.248.255"),
+        #                  ("0.0.0.0/0", "130.56.240.1")]
+        for net_address, gateway in self.static_routes:
+            via_arg = []
+            if gateway != "0.0.0.0/0":
+                via_arg = ['via', gateway]
+            util.subp(
+                ['ip', '-4', 'route', 'add', net_address] + via_arg +
+                ['dev', self.interface], capture=True)
+            self.cleanup_cmds.insert(
+                0, ['ip', '-4', 'route', 'del', net_address] + via_arg +
+                   ['dev', self.interface])
+
     def _bringup_router(self):
         """Perform the ip commands to fully setup the router if needed."""
         # Check if a default route exists and exit if it does