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IPMASQ and lock-up of all terminals



[mod: This is the second time in a week that someone asks this
question: is it a new attack? It sure looks to me like "userland" has
completely locked up, but that the kernel is still working. As an
isolated case, my diagnosis is: You probably have a bad block in your
/bin/login program or something like that. When two people report this
in a week, it's starting to become unlikely that two people have a
hole in their /bin/login program at the same time.... -- REW]

I have a strange situation here that I don't know how to follow up on.  I
have a box setup that is pretty much only to do ipchains for a couple of
computers behind it.  This has occurred for me for both RH6.0 and now RH6.2
beta on an x86.. 

Symptoms:
All attempts to connect remotely receive a connection, but a login prompt
never comes up.
When I went to the console and turned on the monitor, I had the login
prompt, but written on to the screen was the message 
IPMASQ: Reverse ICMP: Checksum error from xxx.xxx.xxx.xxx
where the x's represent and IP address.. message was repeated four times, (I
think).  

I can type in a username and hit return, and then nothing happens and it
does not ask for password or anything.

When I pull up other TTY's  (hitting alt-F1), the messages are not there,
but when I type in a username, again, nothing happens and it never asks for
a password.

ipchains and forwarding continues to function (i.e. they are still connected
through that box), but everything else I can check appears to be locked up.
CTRL-ALT-DEL does nothing, and I have to do a hard reboot.

Is this an error in my IPCHAINS rules, or something else?  What other
information can I provide to help?

Thanks for any help you can give..
James Meriwether



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