netdev - Re: Overflow bug in Vegas

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Date:	Wed, 30 Apr 2008 01:06:27 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	lachlan.andrew@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: Overflow bug in Vegas

From: "Lachlan Andrew" <lachlan.andrew@...il.com>
Date: Wed, 9 Apr 2008 13:57:23 -0700

> Greetings all,
> 
> There is an overflow bug in  net/ipv4/tcp_vegas.c  for large BDPs
> (e.g. 400Mbit/s, 400ms).
> The multiplication  (old_wnd * vegas->baseRTT) << V_PARAM_SHIFT
> overflows a  u32.
> 
> The attached patch relative to 2.6.25-rc7 fixes that.
> 
> (No-one would ever use Vegas on a path like that, but it will affect
> algorithms derived from the Vegas code.  I found the bug while testing
> the Linux port of Microsoft's Compound TCP, from
> <http://netlab.caltech.edu/lachlan/ctcp/>.  That patch is derived from
> Angelo Castellani's which used the Vegas code.)

tcp_veno.c had similar calculations, so I fixed those up too when
I applied your patch.

Thanks.
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