linux-kernel - Re: [PATCH] netfilter: Fix build failure when ipv6 but xt

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Message-ID: <4D9B2BF2.2010606@trash.net>
Date:	Tue, 05 Apr 2011 16:49:22 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	KOVACS Krisztian <hidden@...abit.hu>
CC:	David Miller <davem@...emloft.net>, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: Fix build failure when ipv6 but xt_tproxy
 is built in

Am 05.04.2011 16:43, schrieb KOVACS Krisztian:
> Hi,
> 
> On Mon, 2011-04-04 at 15:54 +0200, Patrick McHardy wrote:
>>>> net/built-in.o: In function `tproxy_tg6_v1':
>>>> /home/rostedt/work/autotest/nobackup/linux-test.git/net/netfilter/xt_TPROXY.c:288: undefined reference to `ipv6_find_hdr'
>>>>
>>>> This happened because the xt_TPROXY code was compiled into the kernel
>>>> proper, but the ipv6 netfilter was compiled as a module. The fix is to
>>>> only enter the code that calls ipv6_find_hdr if ipv6 netfilter is
>>>> compiled into the kernel, or if it is a module, so is the xt_TPROXY
>>>> code.
>>
>> I don't think this is a good fix for the problem since it may lead to
>> the confusing situation that both TPROXY and ip6tables are enabled,
>> but TPROXY has no IPv6 support.
>>
>> I think we should solve this by either adding a Kconfig dependency
>> on (IP6_NF_IPTABLES || IP6_NF_IPTABLES=n) or using ipv6_skip_exthdr()
>> instead of ipv6_find_hdr().
>>
>> Krisztian, what do you think?
> 
> I'd definitely prefer using ipv6_skip_exthdr() instead of playing
> various tricks with the config preprocessor macros.
> 
> What about something like this?
> 
> diff --git a/net/netfilter/xt_TPROXY.c b/net/netfilter/xt_TPROXY.c
> index dcfd57e..1ef0e56 100644
> --- a/net/netfilter/xt_TPROXY.c
> +++ b/net/netfilter/xt_TPROXY.c
> @@ -283,10 +283,10 @@ tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
>         const struct in6_addr *laddr;
>         __be16 lport;
>         int thoff;
> -       int tproto;
> +       u8 tproto = iph->nexthdr;
>  
> -       tproto = ipv6_find_hdr(skb, &thoff, -1, NULL);
> -       if (tproto < 0) {
> +       thoff = ipv6_skip_exthdr(skb, sizeof(*iph), &tproto);
> +       if (thoff < 0) {
>                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
>                 return NF_DROP;
>         }

Looks good to me. Please formally submit this including a Signed-off-by:
line and I'll push it upstream.
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