NetfilterQueue set_payload not working

Question

I use NetfilterQueue and scapy to end the monitoring program and package spoofing.

But I'm just worried that the set_payload () method of the NetfilterQueue module does not seem to work for me.

Here is my source code.

from netfilterqueue import NetfilterQueue as nfqueue
from scapy.all import *
import os
import socket
import re

baidu_ip = socket.gethostbyname('www.baidu.com')
print "Got baidu ip: " + baidu_ip

iptablesr = 'iptables -t mangle -A POSTROUTING -p tcp -j NFQUEUE --queue-num 1'
print("Adding iptable rules :")
print(iptablesr)
os.system(iptablesr)
iptablesr = 'iptables -t mangle -A POSTROUTING -p udp -j NFQUEUE --queue-num 1'
print(iptablesr)
os.system(iptablesr)


def callback(packet):
    modified = False
    sca_pkt = IP(packet.get_payload())

    # This is the main logic, to modify the packet
    try:
        dns_lookup = re.search(r'DNS Qry "([\w\.]+)"', sca_pkt[DNS].summary()).group(1)
        if re.search(r'baidu\.com', dns_lookup) != None:
            sca_pkt[DNS].qd = DNSQR(qname='www.163.com')
            sca_pkt[UDP].len = len(bytes(sca_pkt[UDP]))
            sca_pkt[UDP].chksum = 0x0000
            modified = True
    except:
        pass

    # Accept the modified packet
    if modified == True:
        print 'debug sca_pkt: ' + sca_pkt.summary()
        packet.set_payload(str(sca_pkt))
        print 'debug packet: ' + IP(packet.get_payload()).summary()
        packet.accept()
        return 

    packet.accept()

def main():
    q = nfqueue()
    q.bind(1, callback)
    try:
        q.run()
    except KeyboardInterrupt:
        q.unbind()
        print "Flushing iptables."
        os.system('iptables -F')
        os.system('iptables -F -t mangle')

if __name__ == '__main__':
    main()

And this is the result that I got.

Got baidu ip: 180.97.33.108
Adding iptable rules :
iptables -t mangle -A POSTROUTING -p tcp -j NFQUEUE --queue-num 1
iptables -t mangle -A POSTROUTING -p udp -j NFQUEUE --queue-num 1
debug sca_pkt: IP / UDP / DNS Qry "www.163.com" 
debug packet: IP / UDP / DNS Qry "baidu.com."

You can see from the debug information that set_payload () is not working. (I set the packet to the value shown in sca_pkt, but when I get the final value of the packet payload, it is still the original value)

And I just tried two versions of NetfilterQueue, including the pip version and https://github.com/kti/python-netfilterqueue.git .

So can someone help me? I'm just really interested about that.

Answer 1

, scapy , set_payload .

:

packet.set_payload(str(sca_pkt))

- :

packet.payload = sca_pkt.payload

, UDP. , DNS , :

packet[DNS] = sca_pkt[DNS]