DHCP_am: support multiple nameservers (#4834)

* DHCP_am: support multiple nameservers

* Fix dhcpd IPython test

---------

Co-authored-by: Mike Zeng <mzen17.jp@gmail.com>

Author: gpotter2

scapy/layers/dhcp.py

@@ -61,6 +61,13 @@
 from scapy.error import warning
 from scapy.config import conf
 
+# Typing imports
+from typing import (
+    List,
+    Optional,
+    Union,
+)
+
 dhcpmagic = b"c\x82Sc"
 
 
@@ -601,27 +608,33 @@ class BOOTP_am(AnsweringMachine):
     filter = "udp and port 68 and port 67"
 
     def parse_options(self,
-                      pool=Net("192.168.1.128/25"),
-                      network="192.168.1.0/24",
-                      gw="192.168.1.1",
-                      nameserver=None,
-                      domain=None,
-                      renewal_time=60,
-                      lease_time=1800,
+                      pool: Union[Net, List[str]] = Net("192.168.1.128/25"),
+                      network: str = "192.168.1.0/24",
+                      gw: str = "192.168.1.1",
+                      nameserver: Union[str, List[str]] = None,
+                      domain: Optional[str] = None,
+                      renewal_time: int = 60,
+                      lease_time: int = 1800,
                       **kwargs):
         """
         :param pool: the range of addresses to distribute. Can be a Net,
                      a list of IPs or a string (always gives the same IP).
         :param network: the subnet range
         :param gw: the gateway IP (can be None)
-        :param nameserver: the DNS server IP (by default, same than gw)
+        :param nameserver: the DNS server IP (by default, same than gw).
+            This can also be a list.
         :param domain: the domain to advertise (can be None)
 
         Other DHCP parameters can be passed as kwargs. See DHCPOptions in dhcp.py.
         For instance::
 
             dhcpd(pool=Net("10.0.10.0/24"), network="10.0.0.0/8", gw="10.0.10.1",
                   classless_static_routes=["1.2.3.4/32:9.8.7.6"])
+
+        Other example with different options::
+
+            dhcpd(pool=Net("10.0.10.0/24"), network="10.0.0.0/8", gw="10.0.10.1",
+                  nameserver=["8.8.8.8", "4.4.4.4"], domain="DOMAIN.LOCAL")
         """
         self.domain = domain
         netw, msk = (network.split("/") + ["32"])[:2]
@@ -630,7 +643,13 @@ def parse_options(self,
         self.network = ltoa(atol(netw) & msk)
         self.broadcast = ltoa(atol(self.network) | (0xffffffff & ~msk))
         self.gw = gw
-        self.nameserver = nameserver or gw
+        if nameserver is None:
+            self.nameserver = (gw,)
+        elif isinstance(nameserver, str):
+            self.nameserver = (nameserver,)
+        else:
+            self.nameserver = tuple(nameserver)
+
         if isinstance(pool, str):
             pool = Net(pool)
         if isinstance(pool, Iterable):
@@ -691,7 +710,7 @@ def make_reply(self, req):
                     ("server_id", self.gw),
                     ("domain", self.domain),
                     ("router", self.gw),
-                    ("name_server", self.nameserver),
+                    ("name_server", *self.nameserver),
                     ("broadcast_address", self.broadcast),
                     ("subnet_mask", self.netmask),
                     ("renewal_time", self.renewal_time),

test/answering_machines.uts

@@ -39,12 +39,23 @@ test_am(BOOTP_am,
 def check_DHCP_am_reply(packet):
     assert DHCP in packet and len(packet[DHCP].options)
     assert ("domain", b"localnet") in packet[DHCP].options
+    assert ('name_server', '192.168.1.1') in packet[DHCP].options
+
+def check_ns_DHCP_am_reply(packet):
+    assert DHCP in packet and len(packet[DHCP].options)
+    assert ("domain", b"localnet") in packet[DHCP].options
+    assert ('name_server', '1.1.1.1', '2.2.2.2') in packet[DHCP].options
 
 test_am(DHCP_am,
         Ether()/IP()/UDP()/BOOTP(op=1)/DHCP(options=[('message-type', 'request')]),
         check_DHCP_am_reply,
         domain="localnet")
 
+test_am(DHCP_am,
+        Ether()/IP()/UDP()/BOOTP(op=1)/DHCP(options=[('message-type', 'request')]),
+        check_ns_DHCP_am_reply,
+        domain="localnet",
+        nameserver=["1.1.1.1", "2.2.2.2"])
 
 = ARP_am
 def check_ARP_am_reply(packet):

test/scapy/layers/dhcp.uts

@@ -125,5 +125,14 @@ assert DHCPRevOptions['static-routes'][0] == 33
 
 assert dhcpd
 import IPython
-assert IPython.lib.pretty.pretty(dhcpd) == '<function scapy.ansmachine.dhcpd(self, pool=Net("192.168.1.128/25"), network=\'192.168.1.0/24\', gw=\'192.168.1.1\', nameserver=None, domain=None, renewal_time=60, lease_time=1800, **kwargs)>'
+
+result = IPython.lib.pretty.pretty(dhcpd)
+result
+
+# 3 results depending on the Python version
+assert result in [
+    '<function scapy.ansmachine.dhcpd(self, pool: Union[scapy.base_classes.Net, List[str]] = Net("192.168.1.128/25"), network: str = \'192.168.1.0/24\', gw: str = \'192.168.1.1\', nameserver: Union[str, List[str]] = None, domain: Optional[str] = None, renewal_time: int = 60, lease_time: int = 1800, **kwargs)>',
+    '<function scapy.ansmachine.dhcpd(self, pool: Union[scapy.base_classes.Net, List[str]] = Net("192.168.1.128/25"), network: str = \'192.168.1.0/24\', gw: str = \'192.168.1.1\', nameserver: Union[str, List[str]] = None, domain: Union[str, NoneType] = None, renewal_time: int = 60, lease_time: int = 1800, **kwargs)>',
+    '<function scapy.ansmachine.dhcpd(self, pool=Net("192.168.1.128/25"), network=\'192.168.1.0/24\', gw=\'192.168.1.1\', nameserver=None, domain=None, renewal_time=60, lease_time=1800, **kwargs)>',
+]