netdev - Re: [PATCH bpf-next] net: core: Fix build with CONFIG

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Date:   Thu, 4 Oct 2018 10:48:33 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     netdev@...r.kernel.org, ast@...nel.org
Subject: Re: [PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

On 10/03/2018 07:32 AM, Joe Stringer wrote:
> Stephen Rothwell reports the following link failure with IPv6 as module:
> 
>   x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
>   (.text+0x19219): undefined reference to `__udp6_lib_lookup'
> 
> Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
> compiled into the kernel.
> 
> Signed-off-by: Joe Stringer <joe@...d.net.nz>
> ---
>  net/core/filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 591c698bc517..30c6b2d3ef16 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
>  			sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
>  					       dst4, tuple->ipv4.dport,
>  					       dif, sdif, &udp_table, skb);
> -#if IS_ENABLED(CONFIG_IPV6)
> +#if IS_REACHABLE(CONFIG_IPV6)
>  	} else {
>  		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
>  		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
> 

Applied as a quick fix, thanks Joe, but ideally this should also work when ipv6
is compiled as a module. There's the ipv6_bpf_stub, which does that job for other
helpers that would call into v6 code out of the builtin filter.c, so I think we
should follow the same approach here as well. See commit d74bad4e74ee ("bpf:
Hooks for sys_connect").

Thanks,
Daniel