netdev - Re: query: bnx2 and tg3 don't check tcp and/or ip header length validity?

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Date:	Wed, 14 Oct 2009 14:24:18 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"William Allen Simpson" <william.allen.simpson@...il.com>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: query: bnx2 and tg3 don't check tcp and/or ip header length
 validity?

On Wed, 2009-10-14 at 13:46 -0700, William Allen Simpson wrote:
> William Allen Simpson wrote:
> > My question is whether it would be OK to add a simple test, and set it to
> > zero in case of bad values?
> > 
> Although both are compiled in my build, I've got no way to test them.  I'm
> just going to do the easy thing and set to zero for now.  Somebody that
> knows the code -- who should have done real error checking -- could actually
> write better error checking and comments about the purpose of cramming the
> length of the TCP option field into a tag....

The option length is needed by the hardware to segment a TSO packet into
proper MTU-sized packets.  You'll get malformed packets if the TSO
header is bad.  Setting it to zero perhaps can make these bad packets
more deterministic, but I don't know for sure.

> 
> -		tcp_opt_len = tcp_optlen(skb);
> +		tcp_opt_len = tcp_option_len_th(tcp_hdr(skb));
> +		if (tcp_opt_len < 0)
> +			tcp_opt_len = 0;
> 

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