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Specifying source IP in Linux 2.4.0-test

To: netdev@xxxxxxxxxxx
Subject: Specifying source IP in Linux 2.4.0-test
From: Adam Slattery <aslattery@xxxxxxxxxxxxxx>
Date: Sun, 27 Aug 2000 14:53:50 -0700 (PDT)
Reply-to: aslattery@xxxxxxxxxxxxxx
Sender: owner-netdev@xxxxxxxxxxx
Hi. Hopefully this is the correct mailing list...
Anyway, recently I've been programming with raw IP sockets. I've been working 
with Linux 2.4.0-test{1,6}, and have come across a problem. I have verified 
that my code is in fact correct because it works on 2.2.13 and 2.0.38 (I 
happened to have the source for those kernels).

The problem is that the kernel seems to be ignoring my setsockopt() call that 
is supposed to tell the kernel to use my IP header rather than creating one on 
it's own. When I try to specify a bogus source IP address in my own header, the 
kernel always changes it to whatever IP is on the interface the packet will go 
out on(I haven't tried this on an interface with aliases). I have played with a 
few DoS exploits and whatever other code I could get my hands on to see if IP 
spoofing worked or not, and I have found that it does not. This definately 
seems like a bug (feature?) in 2.4.0 to me.

I've looked for the place where the problem might lie for the past week with no 
luck. I'm starting school again and no longer have much time to do any coding, 
so I figured I would ask some people on a mailing list about this.

If you would like some code to prove my statements above, just ask and i'll 
include it in another posting (or mail it to you directly).

BTW, this seems like a pretty major bug, so I'm extremely suprised that I 
haven't found anybody else with this problem yet.

Adam Slattery

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