[Pkg-nagios-devel] Bug#396337: Acknowledgement (check_tcp:
check_tcp (check_pop) fails on some specific +OK messages)
benoit.panizzon at imp.ch
Tue Oct 31 11:54:23 CET 2006
It looks like we have been able to quite exactly figure out what goes wrong.
From Kernel 2.6.17 on, the tcp_window_scaling code was changed.
Linux starts with very small packets.
Our POP +OK string is exaclty 47 bytes long and split into two reads:
46 bytes + 1 byte
check_tcp apparently fails if a read is split into multiple reads and
terminates thos two reads with \0 and overwrites the first 46 bytes by
terminating them with \0 after the lenght of the second read, thus leaving
something like "+O" or even shorter remaining in the buffer.
If the string is shorter everything is OK as it fits into one read.
If the string is longer, the overwriting happens after the +OK and again the
check is OK.
Quick Fix: Disable TCP Window Scaling:
echo 0 > /proc/sys/net/ipv4/tcp_window_scaling
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