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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 19 Jun 2019 21:57:35 +0200
Message-ID: <CAK8P3a3BPgieF_dUFZoNVOp7avdJwJZn2S1O=EA9DZXu_c59WQ@mail.gmail.com>
Subject: Re: [PATCH] netfilter: synproxy: fix building syncookie calls
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Fernando Fernandez Mancera <ffmancera@riseup.net>,
        wenxu <wenxu@ucloud.cn>,
        netfilter-devel <netfilter-devel@vger.kernel.org>,
        coreteam@netfilter.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>
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On Wed, Jun 19, 2019 at 7:46 PM Pablo Neira Ayuso <pablo@netfilter.org> wrote:
>
> On Wed, Jun 19, 2019 at 02:54:36PM +0200, Arnd Bergmann wrote:
> > When either CONFIG_IPV6 or CONFIG_SYN_COOKIES are disabled, the kernel
> > fails to build:
> >
> > include/linux/netfilter_ipv6.h:180:9: error: implicit declaration of function '__cookie_v6_init_sequence'
> >       [-Werror,-Wimplicit-function-declaration]
> >         return __cookie_v6_init_sequence(iph, th, mssp);
> > include/linux/netfilter_ipv6.h:194:9: error: implicit declaration of function '__cookie_v6_check'
> >       [-Werror,-Wimplicit-function-declaration]
> >         return __cookie_v6_check(iph, th, cookie);
> > net/ipv6/netfilter.c:237:26: error: use of undeclared identifier '__cookie_v6_init_sequence'; did you mean 'cookie_init_sequence'?
> > net/ipv6/netfilter.c:238:21: error: use of undeclared identifier '__cookie_v6_check'; did you mean '__cookie_v4_check'?
> >
> > Fix the IS_ENABLED() checks to match the function declaration
> > and definitions for these.
>
> I made this:
>
> https://patchwork.ozlabs.org/patch/1117735/
>
> Basically it does:
>
> +#endif
> +#if IS_MODULE(CONFIG_IPV6) && defined(CONFIG_SYN_COOKIES)
>         .cookie_init_sequence   = __cookie_v6_init_sequence,
>         .cookie_v6_check        = __cookie_v6_check,
>  #endif
>
> If CONFIG_IPV6=n, then net/ipv6/netfilter.c is never compiled.
>
> Unless I'm missing anything, I'd prefer my patch because it's a bit
> less of ifdefs 8-)

That takes care of the link error, but not the "implicit declaration"
when netfilter_ipv6.h is included without SYN_COOKIES.

My patch addresses both issues together since they are strongly
related.

      Arnd