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import random
from actions.action import Action
import layers.packet
from scapy.all import IP, TCP, fragment
MAX_UINT = 4294967295
class FragmentAction(Action):
Defines the FragmentAction for Geneva - fragments or segments the given packet.
frequency = 2
def __init__(self, environment_id=None, correct_order=None, fragsize=-1, segment=True, overlap=0):
Initializes a fragment action object.
environment_id (str, optional): Environment ID of the strategy this object is a part of
correct_order (bool, optional): Whether or not the fragments/segments should be returned in the correct order
fragsize (int, optional): The index this packet should be cut. Defaults to -1, which cuts it in half.
segment (bool, optional): Whether we should perform fragmentation or segmentation
overlap (int, optional): How many bytes the fragments/segments should overlap
Action.__init__(self, "fragment", "out")
self.enabled = True
self.branching = True
self.terminal = False
self.fragsize = fragsize
self.segment = segment
self.overlap = overlap
if correct_order == None:
self.correct_order = self.get_rand_order()
self.correct_order = correct_order
def get_rand_order(self):
Randomly decides if the fragments should be reversed.
return random.choice([True, False])
def fragment(self, original, fragsize):
Fragments a packet into two, given the size of the first packet (0:fragsize)
Always returns two packets
if fragsize == 0:
frags = [original]
frags = fragment(original, fragsize=fragsize)
# If there were more than 2 fragments, join the loads so we still have 2 packets
if len(frags) > 2:
for frag in frags[2:]:
frags[1]["IP"].load += frag["IP"].load
# After scapy fragmentation, the flags field is set to "MF+DF"
# In order for the packet to remain valid, strip out the "MF"
frags[1]["IP"].flags = "DF"
# If scapy tried to fragment but there were only enough bytes for 1 packet, just duplicate it
elif len(frags) == 1:
return frags[0], frags[1]
def ip_fragment(self, packet, logger):
Perform IP fragmentation.
if not packet.haslayer("IP") or not hasattr(packet["IP"], "load"):
return packet, packet.copy() # duplicate if no TCP or no payload to segment
load = ""
if packet.haslayer("TCP"):
load = bytes(packet["TCP"])
elif packet.haslayer("UDP"):
load = bytes(packet["UDP"])
load = bytes(packet["IP"].load)
# If there is no load, duplicate the packet
if not load:
return packet, packet.copy()
if self.fragsize == -1 or (self.fragsize * 8) > len(load) or len(load) <= 8:
fragsize = int(int(((int(len(load)/2))/8))*8)
frags = self.fragment(packet.copy().packet, fragsize=fragsize)
# packet can be fragmented as requested
frags = self.fragment(packet.copy().packet, fragsize=self.fragsize*8)
packet1 = layers.packet.Packet(frags[0])
packet2 = layers.packet.Packet(frags[1])
if self.correct_order:
return packet1, packet2
return packet2, packet1
def tcp_segment(self, packet, logger):
Segments a packet into two, given the size of the first packet (0:fragsize)
Always returns two packets, since fragment is a branching action, so if we
are unable to segment, it will duplicate the packet.
If overlap is specified, it will select n bytes from the second packet
and append them to the first, and increment the sequence number accordingly
if not packet.haslayer("TCP") or not hasattr(packet["TCP"], "load") or not packet["TCP"].load:
return packet, packet.copy() # duplicate if no TCP or no payload to segment
# Get the original payload and delete it from the packet so it
# doesn't come along when copying the TCP layer
payload = packet["TCP"].load
fragsize = self.fragsize
if self.fragsize == -1 or self.fragsize > len(payload) - 1:
fragsize = int(len(payload)/2)
# Craft new packets
# Make sure we don't go out of bounds by choosing the min
overlap_bytes = min(len(payload[fragsize:]), self.overlap)
# Attach these bytes to the first packet
pkt1 = IP(packet["IP"])/payload[:fragsize + overlap_bytes]
pkt2 = IP(packet["IP"])/payload[fragsize:]
# We cannot rely on scapy's native parsing here - if a previous action has changed the
# fragment offset, scapy will not identify this as TCP, so we must do it for scapy
if not pkt1.haslayer("TCP"):
pkt1 = IP(packet["IP"])/TCP(bytes(pkt1["IP"].load))
if not pkt2.haslayer("TCP"):
pkt2 = IP(packet["IP"])/TCP(bytes(pkt2["IP"].load))
packet1 = layers.packet.Packet(pkt1)
packet2 = layers.packet.Packet(pkt2)
# Reset packet2's SYN number
if packet2["TCP"].seq + fragsize > MAX_UINT:
# Wrap sequence numbers around if greater than MAX_UINT
packet2["TCP"].seq = packet2["TCP"].seq + fragsize - MAX_UINT - 1
packet2["TCP"].seq += fragsize
del packet1["IP"].chksum
del packet2["IP"].chksum
del packet1["IP"].len
del packet2["IP"].len
del packet1["TCP"].chksum
del packet2["TCP"].chksum
del packet1["TCP"].dataofs
del packet2["TCP"].dataofs
if self.correct_order:
return [packet1, packet2]
return [packet2, packet1]
def run(self, packet, logger):
The fragment action fragments each given packet.
logger.debug(" - Fragmenting given packet %s" % str(packet))
if self.segment:
return self.tcp_segment(packet, logger)
return self.ip_fragment(packet, logger)
def __str__(self):
Returns a string representation with the fragsize
s = Action.__str__(self)
if not self.overlap:
ending = "}"
ending = ":" + str(self.overlap) + "}"
if self.segment:
s += "{" + "tcp" + ":" + str(self.fragsize) + ":" + str(self.correct_order) + ending
s += "{" + "ip" + ":"+ str(self.fragsize) + ":" + str(self.correct_order) + ending
return s
def parse(self, string, logger):
Parses a string representation of fragmentation. Nothing particularly special,
but it does check for a the fragsize.
Note that the given logger is a DIFFERENT logger than the logger passed
to the other functions, and they cannot be used interchangeably. This logger
is attached to the main GA driver, and is run outside the evaluator. When the
action is actually run, it's run within the evaluator, which by necessity must
pass in a different logger.
# Count the number of params in this given string
num_parameters = string.count(":")
# If num_parameters is greater than 2, it's not a valid fragment action
if num_parameters == 2:
params = string.split(":")
seg, fragsize, correct_order = params
overlap = 0
if "tcp" in seg:
self.segment = True
self.segment = False
elif num_parameters == 3:
params = string.split(":")
seg, fragsize, correct_order, overlap = params
if overlap.endswith("}"):
overlap = overlap[:-1] # Chop off trailing }
if "tcp" in seg:
self.segment = True
self.segment = False
msg = "Cannot parse fragment action %s" % string
raise Exception(msg)
# Try to convert to int
self.fragsize = int(fragsize)
self.overlap = int(overlap)
except ValueError as e:
msg = "Cannot parse fragment action %s" % string
raise Exception(msg)
# Parse ordering
if correct_order.startswith('True'):
self.correct_order = True
self.correct_order = False
return True
def mutate(self, environment_id=None):
Mutates the fragment action - it either chooses a new segment offset,
switches the packet order, and/or changes whether it segments or fragments.
self.correct_order = self.get_rand_order()
self.segment = random.choice([True, True, True, False])
if self.segment:
if random.random() < 0.5:
self.fragsize = int(random.uniform(1, 60))
self.fragsize = -1
if random.random() < 0.2:
self.fragsize = int(random.uniform(1, 50))
self.fragsize = -1
if random.random() < .5:
# Somewhat aggressively overlap
if random.random() < .5:
if self.fragsize == -1:
self.overlap = 5
self.overlap = int(self.fragsize/2)
self.overlap = int(random.uniform(1, 50))
return self