Python分割故障使用PCAP通过CTYPES

Question

我使用libpcap通过ctypes将嗅探器从C到Python移植。这是Python代码：

import ctypes, sys
from ctypes.util import find_library
if sys.platform == "darwin":
    _pcap = ctypes.cdll.LoadLibrary(find_library("libpcap"))
elif sys.platform == "linux2":
    _pcap = ctypes.cdll.LoadLibrary("libpcap.so")
errbuf = ctypes.create_string_buffer(256)
pcap_lookupdev = _pcap.pcap_lookupdev
pcap_lookupdev.restype = ctypes.c_char_p
dev = pcap_lookupdev(errbuf)
print dev
# create handler
pcap_create = _pcap.pcap_create
handle = pcap_create(dev, errbuf)
print handle
if not handle:
    print "failed creating handler:",errbuf
    exit()
# monitor mode
pcap_can_set_rfmon = _pcap.pcap_can_set_rfmon
print "can rfmon:",pcap_can_set_rfmon(handle)

在Linux上它的工作原理很好，但是在Mac OS X上，当我使用句柄时，它会遇到分割故障。手柄的价值甚至有时为负，有时为正面。我已经尝试将pcap_create的返回类型更改为unsigned int，但这无济于事，但我认为它在OS X下返回错误的类型...

我在C中的两个系统上都进行了printf("size of pcap_t: %zun", sizeof(pcap_t *));，以获取PCAP_T处理程序类型的大小。在Linux上，它说4和OS X 8。

还是我在错误的道路上？有人有想法吗？

Answer 1

数据类型很重要。

您需要告诉CTYPES pcap_create()的返回值是指指针，您需要告诉它，pcap_can_set_rfmon()的参数是指针。

您通过执行此操作

# create handler
pcap_create = _pcap.pcap_create
pcap_create.restype = ctypes.c_void_p
handle = pcap_create(dev, errbuf)
print handle
if not handle:
    print "failed creating handler:",errbuf
    exit()
# monitor mode
pcap_can_set_rfmon = _pcap.pcap_can_set_rfmon
pcap_can_set_rfmon.argtypes = [ctypes.c_void_p]
print "can rfmon:",pcap_can_set_rfmon(handle)

pcap_create.restype = ctypes.c_void_p

和

pcap_can_set_rfmon.argtypes = [ctypes.c_void_p]

这里需要行。该代码将与32位和64位指针一起使用，因此您可以在32位和64位Linux以及32位和64位OS X上使用它（以及32位和64位Solaris以及32位和64位freebsd和...，以及代码所需的任何更改以加载库 - 在大多数*XES共享库中的名称为" .so"，因此，如果您不想要要在其他联合国*XE上使用find_library，Linux代码可能就足够）。

Answer 2

我真的很想来这里发布，因为我也在OS X上遇到了这个问题。我在您的代码中发现的问题是：

handle = pcap_create(dev, errbuf)

您需要设置Restype，这是我的示例，因为这可能会帮助您中的一些人：https：//github.com/killswitch-gui/nix-sniffer-examples

    import ctypes
    import threading
    import sys
    import os
    import errno

    OSX_PCAP_DYLIB = '/usr/lib/libpcap.A.dylib'
    OSX_LIBC_DYLIB = '/usr/lib/libSystem.B.dylib'
    PCAP_ERRBUF_SIZE = 256
    packet_count_limit = ctypes.c_int(1)
    timeout_limit = ctypes.c_int(1000) # In milliseconds 
    err_buf = ctypes.create_string_buffer(PCAP_ERRBUF_SIZE)
    class bpf_program(ctypes.Structure):
        _fields_ = [("bf_len", ctypes.c_int),("bf_insns", ctypes.c_void_p)]
    class pcap_pkthdr(ctypes.Structure):
        _fields_ = [("tv_sec", ctypes.c_long), ("tv_usec", ctypes.c_long), ("caplen", ctypes.c_uint), ("len", ctypes.c_uint)]
    class pcap_stat(ctypes.Structure):
        _fields_ = [("ps_recv",ctypes.c_uint), ("ps_drop",ctypes.c_uint), ("ps_ifdrop", ctypes.c_int)]
    def pkthandler(pkthdr,packet):
        print("In callback:")
        print("pkthdr[0:7]:",pkthdr.contents.len)
        print(pkthdr.contents.tv_sec,pkthdr.contents.caplen,pkthdr.contents.len)
        print(packet.contents[:10])
        print()
    print "-------------------------------------------"
    libc = ctypes.CDLL(OSX_LIBC_DYLIB, use_errno=True)
    if not libc:
        print "Error loading C libary: %s" % errno.errorcode[ctypes.get_errno()]
    print "* C runtime libary loaded: %s" % OSX_LIBC_DYLIB
    pcap = ctypes.CDLL(OSX_PCAP_DYLIB, use_errno=True)
    if not pcap:
        print "Error loading C libary: %s" % errno.errorcode[ctypes.get_errno()]
    print "* C runtime libary loaded: %s" % OSX_PCAP_DYLIB
    print "* C runtime handle at: %s" % pcap
    print "-------------------------------------------"
    pcap_lookupdev = pcap.pcap_lookupdev
    pcap_lookupdev.restype = ctypes.c_char_p
    dev = pcap.pcap_lookupdev()
    print "* Device handle at: %s" % dev
    net = ctypes.c_uint()
    mask = ctypes.c_uint()
    pcap.pcap_lookupnet(dev,ctypes.byref(net),ctypes.byref(mask),err_buf)
    print "* Device IP to bind: %s" % net
    print "* Device net mask: %s" % mask
    #pcap_t *pcap_open_live(const char *device, int snaplen,int promisc, int to_ms, char *errbuf)
    pcap_open_live = pcap.pcap_open_live
    pcap_open_live.restype = ctypes.POINTER(ctypes.c_void_p)
    pcap_create = pcap.pcap_create
    pcap_create.restype = ctypes.c_void_p
    #pcap_handle = pcap.pcap_create(dev, err_buf)
    pcap_handle = pcap.pcap_open_live(dev, 1024, packet_count_limit, timeout_limit, err_buf)
    print "* Live capture device handle at: %s" % pcap_handle 
    pcap_can_set_rfmon = pcap.pcap_can_set_rfmon
    pcap_can_set_rfmon.argtypes = [ctypes.c_void_p]
    if (pcap_can_set_rfmon(pcap_handle) == 1):
        print "* Can set interface in monitor mode"
    pcap_pkthdr_p = ctypes.POINTER(pcap_pkthdr)()
    packetdata = ctypes.POINTER(ctypes.c_ubyte*65536)()
    #print pcap.pcap_next(pcap_handle,ctypes.byref(pcap_pkthdr_p))
    if (pcap.pcap_next_ex(pcap_handle, ctypes.byref(pcap_pkthdr_p), ctypes.byref(packetdata)) == 1):
        print "* Packet captured!"
        pkthandler(pcap_pkthdr_p,packetdata)