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To view the log file:
# tcpdump -n -e -ttt -r /var/log/pflog
Note that using tcpdump(8) to watch the pflog file does not give a real-time display. A real-time display of logged packets is achieved by using the pflog0 interface:
# tcpdump -n -e -ttt -i pflog0
NOTE: When examining the logs, special care should be taken with tcpdump's verbose protocol decoding (activated via the -v command line option). Tcpdump's protocol decoders do not have a perfect security history. At least in theory, a delayed attack could be possible via the partial packet payloads recorded by the logging device. It is recommended practice to move the log files off of the firewall machine before examining them in this way.
Additional care should also be taken to secure access to the logs. By default, pflogd will record 96 bytes of the packet in the log file. Access to the logs could provide partial access to sensitive packet payloads (like telnet(1) or ftp(1) usernames and passwords).
# tcpdump -n -e -ttt -r /var/log/pflog port 80
This can be further refined by limiting the display of packets to a certain host and port combination:
# tcpdump -n -e -ttt -r /var/log/pflog port 80 and host 192.168.1.3
The same idea can be applied when reading from the pflog0 interface:
# tcpdump -n -e -ttt -i pflog0 host 192.168.4.2
Note that this has no impact on which packets are logged to the pflogd log file; the above commands only display packets as they are being logged.
In addition to using the standard tcpdump(8) filter rules, OpenBSD's tcpdump filter language has been extended for reading pflogd output:
Example:
# tcpdump -n -e -ttt -i pflog0 inbound and action block and on wi0
This display the log, in real-time, of inbound packets that were blocked on the wi0 interface.
First we have to create a user, pflogger, with a /sbin/nologin shell. The easiest way to create this user is with adduser(8).
After creating the user pflogger, create the following two scripts:
/etc/pflogrotate
FILE=/home/pflogger/pflog5min.$(date "+%Y%m%d%H%M") kill -ALRM $(cat /var/run/pflogd.pid) if [ $(ls -l /var/log/pflog | cut -d " " -f 8) -gt 24 ]; then mv /var/log/pflog $FILE chown pflogger $FILE kill -HUP $(cat /var/run/pflogd.pid) fi
/home/pflogger/pfl2sysl
for logfile in /home/pflogger/pflog5min* ; do tcpdump -n -e -ttt -r $logfile | logger -t pf -p local0.info rm $logfile done
Edit root's cron job:
# crontab -u root -e
Add the following two lines:
# rotate pf log file every 5 minutes
0-59/5 * * * * /bin/sh /etc/pflogrotate
Create a cron job for user pflogger:
# crontab -u pflogger -e
Add the following two lines:
# feed rotated pflog file(s) to syslog
0-59/5 * * * * /bin/sh /home/pflogger/pfl2sysl
Add the following line to /etc/syslog.conf:
local0.info /var/log/pflog.txt
If you also want to log to a remote log server, add the line:
local0.info @syslogger
Make sure host syslogger has been defined in the hosts(5) file.
Make syslogd notice the changes by restarting it:
# kill -HUP $(cat /var/run/syslog.pid)
All logged packets are now sent to /var/log/pflog.txt. If the second line is added they are sent to the remote logging host syslogger as well.
The script /etc/pflogrotate now processes and then deletes /var/log/pflog so rotation of pflog by newsyslog(8) is no longer necessary and should be disabled. However, /var/log/pflog.txt replaces /var/log/pflog and rotation of it should be activated. Change /etc/newsyslog.conf as follows:
#/var/log/pflog 600 3 250 * ZB /var/run/pflogd.pid /var/log/pflog.txt 600 7 * 24
PF will now log in ASCII to /var/log/pflog.txt. If so configured in /etc/syslog.conf, it will also log to a remote server. The logging is not immediate but can take up to about 5-6 minutes (the cron job interval) before the logged packets appear in the file.
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