I have experienced some strange behavior with my ipt_recent netfilter rules after an uptime of about 25 days. The rules started to block much too early. After rebooting the machine I was able to reproduce the problem for five minutes. This clearly indicated a problem with jiffies (Linux initialized jiffies so that the first roll-over happens five minutes after booting).
A closer look at ipt_recent.c revealed that the time tests did not work like intended if one of the last hits was more than
LONG_MAX jiffies ago or if the list of last hits contained empty slots and jiffies is greater than
To fix this, I replaced jiffies with seconds since ’00:00:00 1970-01-01 UTC’. I have sent the patch to linux-kernel and netfilter-devel. The patch also includes some 64-bit fixes.
May 12th, 2005: The patch has been added to Linux 2.6.12-rc4-mm1
September 8th, 2005: Please note that only the 64-bit parts of my patch have made it into 2.6.12. I’m working on an updated fix for the time comparison problems which will hopefully get accepted for 2.6.14 or later.
July 10th, 2006: The jiffies issue is fixed in the vanilla kernel now. Also note that 2.6.18 will contain a rewrite of ipt_recent.c.