netdev - Re: [PATCH net-next-2.6] syncookies: check decoded options against sysctl settings

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Message-Id: <20100616.135248.39186709.davem@davemloft.net>
Date:	Wed, 16 Jun 2010 13:52:48 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	fw@...len.de
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] syncookies: check decoded options against
 sysctl settings

From: Florian Westphal <fw@...len.de>
Date: Wed, 16 Jun 2010 10:03:09 +0200

> David Miller <davem@...emloft.net> wrote:
>> From: Florian Westphal <fw@...len.de>
>> Date: Sun, 13 Jun 2010 23:34:35 +0200
>> 
>> > -	if (tcp_opt->sack_ok)
>> > -		tcp_sack_reset(tcp_opt);
>> > +	if (tcp_opt->sack_ok && !sysctl_tcp_sack)
>> > +		return false;
>> >  
>> 
>> If you remove the tcp_sack_reset() call here, who is going to
>> do it?
> 
> Right, I should have mentioned that in the changelog, sorry about that.
> 
> Bottom line is that I failed to find out why its needed.
> Both call sites of this function (cookie_v4_check, cookie_v6_check)
> allocate the "struct tcp_options_received" argument on the stack, zero it,
> hand it to tcp_parse_options() and then call cookie_check_timestamp().
> 
> I did not find any place in tcp_parse_options that would cause
> tcp_opt->num_sacks/dsack to become nonzero.
> 
> Even if it can turn nonzero, I do not see any ill effects that might
> happen then. The structure is on the stack and after tcp_parse_options()
> returns only a few selected members are copied to the inet_request_sock.

Please resubmit your patch with these explanations in the commit
message.

Thank you.
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