linux-kernel - Re: Iptable loop during kernel startup

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Date:	Wed, 10 Jan 2007 14:05:21 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Mikael Starvik <mikael.starvik@...s.com>
CC:	'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>,
	Edgar Iglesias <edgar.iglesias@...s.com>,
	'Netfilter Development Mailinglist' 
	<netfilter-devel@...ts.netfilter.org>
Subject: Re: Iptable loop during kernel startup

Mikael Starvik wrote:
> Ok, this is what happens:
> 
> iptable_filter sets up initial_table.
> The part that says { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" }
>   initializes a xt_entry_target struct. target_size gets the value 
>   0x24 and name "". 
> This is copied to loc_cpu_entry in iptables.c:ipt_register_table() 
>   and translate_table is called
> translate_table calls IPT_ENTRY_ITERATE with the 
>   check_entry_function
> check_entry does t->u.kernel.target = target;
> 
> On this particular architecture u.user.name and u.kernel.target in 
> struct xt_entry_target has the same address (because of the union). So 
> name that was previously "" gets mangled here.
> 
> check_entry returns into translate_table which calls mark_source_chains
> mark_source_chains compares t->target.u.user.name with 
> IPT_STANDARD_TARGET. name has been mangled above and the comparision 
> fails. On my ARM platform name has not been mangled (I guess this is 
> because target and name doesn't share address by I haven't checked).
> 
> So... Is it really correct to modify the target pointer there?


Please try the latest -stable kernel, this should be fixed already.
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