Hi Daniel,

On Tue, Dec 31, 2013 at 04:28:39PM +0100, Daniel Borkmann wrote:
> diff --git a/net/netfilter/nf_nat_irc.c b/net/netfilter/nf_nat_irc.c
> index f02b360..fbbb1e6 100644
> --- a/net/netfilter/nf_nat_irc.c
> +++ b/net/netfilter/nf_nat_irc.c
> @@ -34,10 +34,14 @@ static unsigned int help(struct sk_buff *skb,
>  			 struct nf_conntrack_expect *exp)
>  {
>  	char buffer[sizeof("4294967296 65635")];
> +	struct nf_conn *ct = exp->master;
> +	union nf_inet_addr newaddr;
>  	u_int16_t port;
>  	unsigned int ret;
>  
>  	/* Reply comes from server. */
> +	newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
> +
>  	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
>  	exp->dir = IP_CT_DIR_REPLY;
>  	exp->expectfn = nf_nat_follow_master;
> @@ -57,17 +61,41 @@ static unsigned int help(struct sk_buff *skb,
>  	}
>  
>  	if (port == 0) {
> -		nf_ct_helper_log(skb, exp->master, "all ports in use");
> +		nf_ct_helper_log(skb, ct, "all ports in use");
>  		return NF_DROP;
>  	}
>  
> -	ret = nf_nat_mangle_tcp_packet(skb, exp->master, ctinfo,
> -				       protoff, matchoff, matchlen, buffer,
> -				       strlen(buffer));
> +	/* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
> +	 * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
> +	 * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
> +	 * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
> +	 * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
> +	 *
> +	 * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
> +	 *                        255.255.255.255==4294967296, 10 digits)
> +	 * P:         bound port (min 1 d, max 5d (65635))
> +	 * F:         filename   (min 1 d )
> +	 * S:         size       (min 1 d )
> +	 * 0x01, \n:  terminators
> +	 */
> +	/* AAA = "us", ie. where server normally talks to. */
> +	if (nf_ct_l3num(ct) == NFPROTO_IPV4) {
> +		snprintf(buffer, sizeof(buffer), "%u %u",
> +			 ntohl(newaddr.ip), port);
> +		pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n",
> +			 buffer, &newaddr.ip, port);
> +	} else {
> +		nf_ct_helper_log(skb, ct, "IPv6 DCC unsupported for now");
> +		return NF_DROP;
> +	}

I have mangled your patch (see attachment) to remove this branch since
there is real IPv6 support for IRC yet in master. We'll need to
revisit this anyway when finishing IPv6 support to the IRC helper. Let
me know if you have any concern with this. Thanks.