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, 90 insertions, 0 deletions

diff --git a/cloudinit/net/dhcp.py b/cloudinit/net/dhcp.py
index c98a97cd..17379918 100644
--- a/cloudinit/net/dhcp.py
+++ b/cloudinit/net/dhcp.py
@@ -92,10 +92,14 @@ class EphemeralDHCPv4(object):
         nmap = {'interface': 'interface', 'ip': 'fixed-address',
                 'prefix_or_mask': 'subnet-mask',
                 'broadcast': 'broadcast-address',
+                'static_routes': 'rfc3442-classless-static-routes',
                 'router': 'routers'}
         kwargs = dict([(k, self.lease.get(v)) for k, v in nmap.items()])
         if not kwargs['broadcast']:
             kwargs['broadcast'] = bcip(kwargs['prefix_or_mask'], kwargs['ip'])
+        if kwargs['static_routes']:
+            kwargs['static_routes'] = (
+                parse_static_routes(kwargs['static_routes']))
         if self.connectivity_url:
             kwargs['connectivity_url'] = self.connectivity_url
         ephipv4 = EphemeralIPv4Network(**kwargs)
@@ -272,4 +276,90 @@ def networkd_get_option_from_leases(keyname, leases_d=None):
             return data[keyname]
     return None
 
+
+def parse_static_routes(rfc3442):
+    """ parse rfc3442 format and return a list containing tuple of strings.
+
+    The tuple is composed of the network_address (including net length) and
+    gateway for a parsed static route.
+
+    @param rfc3442: string in rfc3442 format
+    @returns: list of tuple(str, str) for all valid parsed routes until the
+              first parsing error.
+
+    E.g.
+    sr = parse_state_routes("32,169,254,169,254,130,56,248,255,0,130,56,240,1")
+    sr = [
+        ("169.254.169.254/32", "130.56.248.255"), ("0.0.0.0/0", "130.56.240.1")
+    ]
+
+    Python version of isc-dhclient's hooks:
+       /etc/dhcp/dhclient-exit-hooks.d/rfc3442-classless-routes
+    """
+    # raw strings from dhcp lease may end in semi-colon
+    rfc3442 = rfc3442.rstrip(";")
+    tokens = rfc3442.split(',')
+    static_routes = []
+
+    def _trunc_error(cidr, required, remain):
+        msg = ("RFC3442 string malformed.  Current route has CIDR of %s "
+               "and requires %s significant octets, but only %s remain. "
+               "Verify DHCP rfc3442-classless-static-routes value: %s"
+               % (cidr, required, remain, rfc3442))
+        LOG.error(msg)
+
+    current_idx = 0
+    for idx, tok in enumerate(tokens):
+        if idx < current_idx:
+            continue
+        net_length = int(tok)
+        if net_length in range(25, 33):
+            req_toks = 9
+            if len(tokens[idx:]) < req_toks:
+                _trunc_error(net_length, req_toks, len(tokens[idx:]))
+                return static_routes
+            net_address = ".".join(tokens[idx+1:idx+5])
+            gateway = ".".join(tokens[idx+5:idx+req_toks])
+            current_idx = idx + req_toks
+        elif net_length in range(17, 25):
+            req_toks = 8
+            if len(tokens[idx:]) < req_toks:
+                _trunc_error(net_length, req_toks, len(tokens[idx:]))
+                return static_routes
+            net_address = ".".join(tokens[idx+1:idx+4] + ["0"])
+            gateway = ".".join(tokens[idx+4:idx+req_toks])
+            current_idx = idx + req_toks
+        elif net_length in range(9, 17):
+            req_toks = 7
+            if len(tokens[idx:]) < req_toks:
+                _trunc_error(net_length, req_toks, len(tokens[idx:]))
+                return static_routes
+            net_address = ".".join(tokens[idx+1:idx+3] + ["0", "0"])
+            gateway = ".".join(tokens[idx+3:idx+req_toks])
+            current_idx = idx + req_toks
+        elif net_length in range(1, 9):
+            req_toks = 6
+            if len(tokens[idx:]) < req_toks:
+                _trunc_error(net_length, req_toks, len(tokens[idx:]))
+                return static_routes
+            net_address = ".".join(tokens[idx+1:idx+2] + ["0", "0", "0"])
+            gateway = ".".join(tokens[idx+2:idx+req_toks])
+            current_idx = idx + req_toks
+        elif net_length == 0:
+            req_toks = 5
+            if len(tokens[idx:]) < req_toks:
+                _trunc_error(net_length, req_toks, len(tokens[idx:]))
+                return static_routes
+            net_address = "0.0.0.0"
+            gateway = ".".join(tokens[idx+1:idx+req_toks])
+            current_idx = idx + req_toks
+        else:
+            LOG.error('Parsed invalid net length "%s".  Verify DHCP '
+                      'rfc3442-classless-static-routes value.', net_length)
+            return static_routes
+
+        static_routes.append(("%s/%s" % (net_address, net_length), gateway))
+
+    return static_routes
+
 # vi: ts=4 expandtab