netdev - Re: [PATCH] Fix corrupt TCP packets when options space overflows with MD5SIG enabled

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Message-Id: <20080603.094400.267474563.davem@davemloft.net>
Date:	Tue, 03 Jun 2008 09:44:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	agl@...erialviolet.org
Cc:	jmorris@...ei.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Fix corrupt TCP packets when options space overflows
 with MD5SIG enabled

From: "Adam Langley" <agl@...erialviolet.org>
Date: Tue, 3 Jun 2008 09:31:02 -0700

> It looks, on second glance, that this code in
> tcp_build_and_update_options will include the options even though we
> calculated the size without:
> 
> if (tp->rx_opt.eff_sacks) {
> 	struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack :
> tp->selective_acks;
> 	int this_sack;
> 
> 	*ptr++ = htonl((TCPOPT_NOP  << 24) |
> 		       (TCPOPT_NOP  << 16) |
> 		       (TCPOPT_SACK <<  8) |
> 		       (TCPOLEN_SACK_BASE + (tp->rx_opt.eff_sacks *
> 			     TCPOLEN_SACK_PERBLOCK)));
> ...
> 
> Unless I'm missing something, that patch was incomplete and we're
> still sending invalid packets on in the MD5SIG + SACK case.

That's right, the code assumes there is always enough space for
the SACK blocks.
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