firewall - With Linux iptables, is it possible to log the process/command name that initiates an outbound connection?

I would like to keep track of the processes that initiate outbound connections on a Linux desktop. The best I can come up with is this:

iptables -A OUTPUT -m state --state NEW -j LOG --log-uid

This logs the uid/gid that initiates the connection, but not the process/command name or even the pid. If I could just get the pid, I could probably whip up a script that pulls the process name when the log is written, but it seems like that is not even possible.

Ideally I'd also like to log the processes that accept incoming connections too.

Any ideas how this might be possible with iptables [or anything else] on a Linux box?

Answer

You could write a program to monitor /proc/net/tcp, whose output looks like this:

obi-wan ~ # cat /proc/net/tcp
  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
   0: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 4847458 1 e6060560 300 0 0 2 -1
   1: 00000000:04D2 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 4847477 1 f2e64da0 300 0 0 2 -1
   2: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 7109 1 f2e65ac0 300 0 0 2 -1
   3: 0100007F:177A 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1000        0 4864457 1 d2726540 300 0 0 2 -1
   4: 00000000:01BB 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 4847462 1 e60609c0 300 0 0 2 -1
   5: 6B00A8C0:0016 30F4B5CA:C3AB 01 00000044:00000000 01:00000031 00000000     0        0 4982752 3 f2e64940 55 4 0 2 -1
   6: 0100007F:B143 0100007F:BC5E 01 00000000:00000000 00:00000000 00000000  1000        0 2130283 1 d59cce40 21 4 1 2 -1
   7: 0100007F:BC5E 0100007F:B143 01 00000000:00000000 00:00000000 00000000  1000        0 2130285 1 d59cd2a0 21 4 0 2 -1
   8: 6B00A8C0:0016 3276C35B:8E11 01 00000000:00000000 02:000ADAB1 00000000     0        0 4982629 2 d2727260 40 4 8 2 2
   9: 6B00A8C0:0016 6500A8C0:DD5D 01 00000538:00000000 01:00000029 00000000     0        0 4864416 5 e6061b40 42 12 27 3 -1

You can then relate opened ports to inodes, which can be related back to processes and file descriptors by doing readlink on the file descriptors listed for each process:

obi-wan ~ # readlink /proc/28850/fd/3
socket:[4847458]

See here that inode 4847458 corresponds to the first tcp socket in the list above. The output of netstat -tapn verifies this for me (and recall that 0x50 == 80):

obi-wan ~ # netstat -tapn
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN     28850/cherokee-work

When the monitor program notices a change in /proc/net/tcp, parse the data and determine if the change is a newly opened socket. Then you could just enumerate all the file descriptors for each process listed in /proc, doing readlink on each on to find the matching inode. Once you find that, you have the owning pid, from which you can get anything else you might want, particularly if you have process accounting on.

If you don't need your notification to be instantaneous, then your monitor program could use a slow poll (perhaps a period of 50ms or 100ms, or even 1000ms).