[英]Python packet sniffer using ctypes crashes when copying socket buffer
我试图捕获IP数据包的前20个字节(完整数据包减去选项),填充ctype
成员的struct
,然后在屏幕上显示我想要的信息(协议,源和目标地址)。 我的IP类别如下:
import socket
import os
import struct
from ctypes import *
# host to listen on
host = "192.168.0.187"
# our IP header
class IP(Structure):
_fields_ = [
("ihl", c_ubyte, 4),
("version", c_ubyte, 4),
("tos", c_ubyte),
("len", c_ushort),
("id", c_ushort),
("offset", c_ushort),
("ttl", c_ubyte),
("protocol_num", c_ubyte),
("sum", c_ushort),
("src", c_ulong),
("dst", c_ulong)
]
def __new__(self, socket_buffer=None):
return self.from_buffer_copy(socket_buffer)
def __init__(self, socket_buffer=None):
# map protocol constants to their names
self.protocol_map = {1:"ICMP", 6:"TCP", 17:"UDP"}
# human readable IP addresses
self.src_address = socket.inet_ntoa(struct.pack("<L",self.src))
self.dst_address = socket.inet_ntoa(struct.pack("<L",self.dst))
# human readable protocol
try:
self.protocol = self.protocol_map[self.protocol_num]
except:
self.protocol = str(self.protocol_num)
现在,我创建套接字,将其绑定到主机,然后循环获取数据包:
# create socket and bind to public interface (os dependent)
if os.name == "nt":
socket_protocol = socket.IPPROTO_IP
else:
socket_protocol = socket.IPPROTO_ICMP
# create raw socket
sniffer = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket_protocol)
sniffer.bind((host, 0))
# include header information
sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
if os.name == "nt":
sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
try:
while True:
# read in a packet
raw_buffer = sniffer.recvfrom(65565)[0]
# create an IP header from the first 20 bytes of the buffer
ip_header = IP(raw_buffer[0:20])
# print out the protocol that was detected and the hosts
print "Protocol: %s %s -> %s" % (ip_header.protocol, ip_header.src_¬
address, ip_header.dst_address)
# handle CTRL-C
except KeyboardInterrupt:
# if we're using Windows, turn off promiscuous mode
if os.name == "nt":
sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)
当使用c_ulong
作为"src"
和"dst"
_fields_
struct
成员的数据类型运行时,出现以下错误(在一个终端上运行,而在另一个终端上ping nostarch.com):
我推测c_ulong
的大小可能大于一个字节,因此放弃了我对前20个字节的要求(我对python非常c_ulong
)。 然后,我将c_ulong
更改为c_ushort
并再次运行:
实际ping路径:
因此,尽管脚本运行无误,但它切断了src
和dst
地址。
当我告诉我只想要前20个字节时,为什么要求至少32个字节?
(我在使用Python 2.7在Win7主机上运行的Kali64 VBox VM中)
任何帮助表示赞赏。
IP
的大小应该被验证,即
print(sizeof(IP))
应该返回20个字节。 由于对于64位linux, ctypes.u_long
为8,因此大小为32字节(由于填充而增加了4个字节,由于整数而导致了8个字节)。 使用ctypes.u_int
或显式大小,如下所示:
from ctypes import *
class IP(Structure):
_fields_ = [ ("version", c_uint8, 4),
("ihl", c_uint8, 4),
("tos", c_uint8),
("len", c_uint16),
("id", c_uint16),
("offset", c_uint16),
("ttl", c_uint8),
("protocol_num", c_uint8),
("sum", c_uint16),
("src", c_uint32),
("dst", c_uint32) ]
print(sizeof(IP))
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