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

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Message-ID: <1302014626.67568.1.camel@nienna.balabit>
Date:	Tue, 05 Apr 2011 16:43:46 +0200
From:	KOVACS Krisztian <hidden@...abit.hu>
To:	Patrick McHardy <kaber@...sh.net>
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

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;
        }

--
KOVACS Krisztian

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