python bind socket.error: [Errno 13] Permission denied

Question

I have a python script which gets packets from a remote machine and writes them (os.write(self.tun_fd.fileno(), ''.join(packet))) to a tun interface gr3:

Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00   inet addr:10.0.0.6  P-t-P:10.0.0.8  Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1 RX packets:61 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500  RX bytes:5124 (5.0 KiB)  TX bytes:0 (0.0 b) 

I would like to receive those packets via a separate pong script as follows:

import threading, os, sys, fcntl, struct, socket from fcntl import ioctl from packet import Packet  HOST = '10.0.0.6' PORT = 111 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind((HOST, PORT)) s.listen(1) conn, addr = s.accept() print 'Connected by', addr while 1:     data = conn.recv(1024)     if not data: break     else: print data         conn.sendall(data) conn.close() 

I got this error :

s.bind((HOST, PORT)) File "<string>", line 1, in bind socket.error: [Errno 13] Permission denied 

Answer 1

You can't bind to port numbers lower than 1024 as a unprivileged user.

So you should either:

• Use a port number larger than 1024 (recommended)
• Or run the script as a privileged user

Harder, but more secure solution if it's really necessary to accept from 111:

• Run the as unprivileged on a higher port, and forward port 111 to it externally.