Skip to content

Commit

Permalink
[dhcp_relay] More detailed crafting and strict testing of OFFER and A…
Browse files Browse the repository at this point in the history 
…CK packets (#908)
  • Loading branch information
@jleveque @lguohan
jleveque authored and lguohan committed May 17, 2019
1 parent cbcc9cd commit 0067126
Showing 1 changed file with 121 additions and 25 deletions.
146 changes: 121 additions & 25 deletions ansible/roles/test/files/ptftests/dhcp_relay_test.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -214,6 +214,46 @@ def create_dhcp_offer_packet(self):
dhcp_lease=self.LEASE_TIME,
padding_bytes=0)

def create_dhcp_offer_relayed_packet(self):
my_chaddr = ''.join([chr(int(octet, 16)) for octet in self.client_mac.split(':')])

# Relay modifies the DHCPOFFER message in the following ways:
# 1.) Replaces the source MAC with the MAC of the interface it received it on
# 2.) Replaces the destination MAC with boradcast (ff:ff:ff:ff:ff:ff)
# 3.) Replaces the source IP with the IP of the interface which the relay
# received it on
# 4.) Replaces the destination IP with broadcast (255.255.255.255)
# 5.) Replaces the destination port with the DHCP client port (68)
ether = scapy.Ether(dst=self.BROADCAST_MAC, src=self.relay_iface_mac, type=0x0800)
ip = scapy.IP(src=self.relay_iface_ip, dst=self.BROADCAST_IP, len=290, ttl=64)
udp = scapy.UDP(sport=self.DHCP_SERVER_PORT, dport=self.DHCP_CLIENT_PORT, len=262)
bootp = scapy.BOOTP(op=2,
htype=1,
hlen=6,
hops=0,
xid=0,
secs=0,
flags=0,
ciaddr=self.DEFAULT_ROUTE_IP,
yiaddr=self.client_ip,
siaddr=self.server_ip,
giaddr=self.relay_iface_ip,
chaddr=my_chaddr)
bootp /= scapy.DHCP(options=[('message-type', 'offer'),
('server_id', self.server_ip),
('lease_time', self.LEASE_TIME),
('subnet_mask', self.client_subnet),
('end')])

# TODO: Need to add this to the packet creation functions in PTF code first!
# If our bootp layer is too small, pad it
#pad_bytes = self.DHCP_PKT_BOOTP_MIN_LEN - len(bootp)
#if pad_bytes > 0:
# bootp /= scapy.PADDING('\x00' * pad_bytes)

pkt = ether / ip / udp / bootp
return pkt

def create_dhcp_request_packet(self):
return testutils.dhcp_request_packet(eth_client=self.client_mac,
ip_server=self.server_ip,
Expand Down Expand Up @@ -272,6 +312,47 @@ def create_dhcp_ack_packet(self):
dhcp_lease=self.LEASE_TIME,
padding_bytes=0)

def create_dhcp_ack_relayed_packet(self):
my_chaddr = ''.join([chr(int(octet, 16)) for octet in self.client_mac.split(':')])

# Relay modifies the DHCPACK message in the following ways:
# 1.) Replaces the source MAC with the MAC of the interface it received it on
# 2.) Replaces the destination MAC with boradcast (ff:ff:ff:ff:ff:ff)
# 3.) Replaces the source IP with the IP of the interface which the relay
# received it on
# 4.) Replaces the destination IP with broadcast (255.255.255.255)
# 5.) Replaces the destination port with the DHCP client port (68)
ether = scapy.Ether(dst=self.BROADCAST_MAC, src=self.relay_iface_mac, type=0x0800)
ip = scapy.IP(src=self.relay_iface_ip, dst=self.BROADCAST_IP, len=290, ttl=64)
udp = scapy.UDP(sport=self.DHCP_SERVER_PORT, dport=self.DHCP_CLIENT_PORT, len=262)
bootp = scapy.BOOTP(op=2,
htype=1,
hlen=6,
hops=0,
xid=0,
secs=0,
flags=0,
ciaddr=self.DEFAULT_ROUTE_IP,
yiaddr=self.client_ip,
siaddr=self.server_ip,
giaddr=self.relay_iface_ip,
chaddr=my_chaddr)
bootp /= scapy.DHCP(options=[('message-type', 'ack'),
('server_id', self.server_ip),
('lease_time', self.LEASE_TIME),
('subnet_mask', self.client_subnet),
('end')])

# TODO: Need to add this to the packet creation functions in PTF code first!
# If our bootp layer is too small, pad it
#pad_bytes = self.DHCP_PKT_BOOTP_MIN_LEN - len(bootp)
#if pad_bytes > 0:
# bootp /= scapy.PADDING('\x00' * pad_bytes)

pkt = ether / ip / udp / bootp
return pkt



"""
Send/receive functions
Expand Down Expand Up @@ -318,9 +399,10 @@ def verify_relayed_discover(self):
masked_discover.set_do_not_care_scapy(scapy.PADDING, "load")

# Count the number of these packets received on the ports connected to our leaves
num_expected_packets = self.num_dhcp_servers
discover_count = testutils.count_matched_packets_all_ports(self, masked_discover, self.server_port_indices)
self.assertTrue(discover_count == self.num_dhcp_servers,
"Failed: Discover count of %d != %d (num_dhcp_servers)" % (discover_count, self.num_dhcp_servers))
self.assertTrue(discover_count == num_expected_packets,
"Failed: Discover count of %d != %d" % (discover_count, num_expected_packets))

# Simulate a DHCP server sending a DHCPOFFER message to client.
# We do this by injecting a DHCPOFFER message on the link connected to one
Expand All @@ -331,24 +413,31 @@ def server_send_offer(self):

# Verify that the DHCPOFFER would be received by our simulated client
def verify_offer_received(self):
dhcp_offer = self.create_dhcp_offer_packet()
dhcp_offer = self.create_dhcp_offer_relayed_packet()

masked_offer = Mask(dhcp_offer)
masked_offer.set_do_not_care_scapy(scapy.Ether, "src")
masked_offer.set_do_not_care_scapy(scapy.Ether, "dst")

masked_offer.set_do_not_care_scapy(scapy.IP, "version")
masked_offer.set_do_not_care_scapy(scapy.IP, "ihl")
masked_offer.set_do_not_care_scapy(scapy.IP, "tos")
masked_offer.set_do_not_care_scapy(scapy.IP, "len")
masked_offer.set_do_not_care_scapy(scapy.IP, "id")
masked_offer.set_do_not_care_scapy(scapy.IP, "flags")
masked_offer.set_do_not_care_scapy(scapy.IP, "frag")
masked_offer.set_do_not_care_scapy(scapy.IP, "ttl")
masked_offer.set_do_not_care_scapy(scapy.IP, "proto")
masked_offer.set_do_not_care_scapy(scapy.IP, "chksum")
masked_offer.set_do_not_care_scapy(scapy.IP, "src")
masked_offer.set_do_not_care_scapy(scapy.IP, "dst")
masked_offer.set_do_not_care_scapy(scapy.IP, "options")

masked_offer.set_do_not_care_scapy(scapy.UDP, "len")
masked_offer.set_do_not_care_scapy(scapy.UDP, "chksum")
masked_offer.set_do_not_care_scapy(scapy.UDP, "dport")

# Mask out lease time since it can change depending on when the server receives the request
# Lease time in ack can be slightly different than in offer, since lease time varies slightly
# We also want to ignore the checksums since they will vary a bit depending on the timestamp
# Offset is byte 292, 6 byte field, set_do_not_care() expects values in bits
masked_offer.set_do_not_care((self.DHCP_LEASE_TIME_OFFSET * 8), (self.DHCP_LEASE_TIME_LEN * 8))
masked_offer.set_do_not_care_scapy(scapy.BOOTP, "sname")
masked_offer.set_do_not_care_scapy(scapy.BOOTP, "file")

masked_offer.set_do_not_care_scapy(scapy.DHCP, "lease_time")

#masked_offer.set_do_not_care_scapy(scapy.PADDING, "load")

# NOTE: verify_packet() will fail for us via an assert, so no need to check a return value here
testutils.verify_packet(self, masked_offer, self.client_port_index)
Expand Down Expand Up @@ -390,9 +479,10 @@ def verify_relayed_request(self):
masked_request.set_do_not_care_scapy(scapy.BOOTP, "file")

# Count the number of these packets received on the ports connected to our leaves
num_expected_packets = self.num_dhcp_servers
request_count = testutils.count_matched_packets_all_ports(self, masked_request, self.server_port_indices)
self.assertTrue(request_count == self.num_dhcp_servers,
"Failed: Request count of %d != %d (num_dhcp_servers)" % (request_count, self.num_dhcp_servers))
self.assertTrue(request_count == num_expected_packets,
"Failed: Request count of %d != %d" % (request_count, num_expected_packets))

# Simulate a DHCP server sending a DHCPOFFER message to client from one of our leaves
def server_send_ack(self):
Expand All @@ -401,23 +491,29 @@ def server_send_ack(self):

# Verify that the DHCPACK would be received by our simulated client
def verify_ack_received(self):
dhcp_ack = self.create_dhcp_ack_packet()
dhcp_ack = self.create_dhcp_ack_relayed_packet()

# Mask out lease time, ip checksum, udp checksum (explanation above)
masked_ack = Mask(dhcp_ack)

masked_ack.set_do_not_care_scapy(scapy.Ether, "src")
masked_ack.set_do_not_care_scapy(scapy.Ether, "dst")

masked_ack.set_do_not_care_scapy(scapy.IP, "version")
masked_ack.set_do_not_care_scapy(scapy.IP, "ihl")
masked_ack.set_do_not_care_scapy(scapy.IP, "tos")
masked_ack.set_do_not_care_scapy(scapy.IP, "len")
masked_ack.set_do_not_care_scapy(scapy.IP, "id")
masked_ack.set_do_not_care_scapy(scapy.IP, "flags")
masked_ack.set_do_not_care_scapy(scapy.IP, "frag")
masked_ack.set_do_not_care_scapy(scapy.IP, "ttl")
masked_ack.set_do_not_care_scapy(scapy.IP, "proto")
masked_ack.set_do_not_care_scapy(scapy.IP, "chksum")
masked_ack.set_do_not_care_scapy(scapy.IP, "src")
masked_ack.set_do_not_care_scapy(scapy.IP, "dst")
masked_ack.set_do_not_care_scapy(scapy.IP, "options")

masked_ack.set_do_not_care_scapy(scapy.UDP, "len")
masked_ack.set_do_not_care_scapy(scapy.UDP, "chksum")
masked_ack.set_do_not_care_scapy(scapy.UDP, "dport")

# Also mask out lease time (see comment in verify_offer_received() above)
masked_ack.set_do_not_care((self.DHCP_LEASE_TIME_OFFSET * 8), (self.DHCP_LEASE_TIME_LEN * 8))
masked_ack.set_do_not_care_scapy(scapy.BOOTP, "sname")
masked_ack.set_do_not_care_scapy(scapy.BOOTP, "file")

masked_ack.set_do_not_care_scapy(scapy.DHCP, "lease_time")

# NOTE: verify_packet() will fail for us via an assert, so no need to check a return value here
testutils.verify_packet(self, masked_ack, self.client_port_index)
Expand Down

0 comments on commit 0067126

Please sign in to comment.