Subject: Re: [PATCH net-next 5/5] net: move the nat function to nf_nat_core for ovs and tc

From: Pablo Neira Ayuso <[email-masked]>
Date: Wed, 16 Nov 2022 22:54:26 +0100

On Tue, Nov 15, 2022 at 10:50:57AM -0500, Xin Long wrote:
> diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
> index e29e4ccb5c5a..1c72b8caa24e 100644
> --- a/net/netfilter/nf_nat_core.c
> +++ b/net/netfilter/nf_nat_core.c
> @@ -784,6 +784,137 @@ nf_nat_inet_fn(void *priv, struct sk_buff *skb,
>  }
>  EXPORT_SYMBOL_GPL(nf_nat_inet_fn);
>  
> +/* Modelled after nf_nat_ipv[46]_fn().
> + * range is only used for new, uninitialized NAT state.
> + * Returns either NF_ACCEPT or NF_DROP.
> + */
> +static int nf_ct_nat_execute(struct sk_buff *skb, struct nf_conn *ct,
> +			     enum ip_conntrack_info ctinfo, int *action,
> +			     const struct nf_nat_range2 *range,
> +			     enum nf_nat_manip_type maniptype)
> +{
> +	__be16 proto = skb_protocol(skb, true);
> +	int hooknum, err = NF_ACCEPT;
> +
> +	/* See HOOK2MANIP(). */
> +	if (maniptype == NF_NAT_MANIP_SRC)
> +		hooknum = NF_INET_LOCAL_IN; /* Source NAT */
> +	else
> +		hooknum = NF_INET_LOCAL_OUT; /* Destination NAT */
> +
> +	switch (ctinfo) {
> +	case IP_CT_RELATED:
> +	case IP_CT_RELATED_REPLY:
> +		if (proto == htons(ETH_P_IP) &&
> +		    ip_hdr(skb)->protocol == IPPROTO_ICMP) {
> +			if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
> +							   hooknum))
> +				err = NF_DROP;
> +			goto out;
> +		} else if (IS_ENABLED(CONFIG_IPV6) && proto == htons(ETH_P_IPV6)) {
> +			__be16 frag_off;
> +			u8 nexthdr = ipv6_hdr(skb)->nexthdr;
> +			int hdrlen = ipv6_skip_exthdr(skb,
> +						      sizeof(struct ipv6hdr),
> +						      &nexthdr, &frag_off);
> +
> +			if (hdrlen >= 0 && nexthdr == IPPROTO_ICMPV6) {
> +				if (!nf_nat_icmpv6_reply_translation(skb, ct,
> +								     ctinfo,
> +								     hooknum,
> +								     hdrlen))
> +					err = NF_DROP;
> +				goto out;
> +			}
> +		}
> +		/* Non-ICMP, fall thru to initialize if needed. */
> +		fallthrough;
> +	case IP_CT_NEW:
> +		/* Seen it before?  This can happen for loopback, retrans,
> +		 * or local packets.
> +		 */
> +		if (!nf_nat_initialized(ct, maniptype)) {
> +			/* Initialize according to the NAT action. */
> +			err = (range && range->flags & NF_NAT_RANGE_MAP_IPS)
> +				/* Action is set up to establish a new
> +				 * mapping.
> +				 */
> +				? nf_nat_setup_info(ct, range, maniptype)
> +				: nf_nat_alloc_null_binding(ct, hooknum);
> +			if (err != NF_ACCEPT)
> +				goto out;
> +		}
> +		break;
> +
> +	case IP_CT_ESTABLISHED:
> +	case IP_CT_ESTABLISHED_REPLY:
> +		break;
> +
> +	default:
> +		err = NF_DROP;
> +		goto out;
> +	}
> +
> +	err = nf_nat_packet(ct, ctinfo, hooknum, skb);
> +	if (err == NF_ACCEPT)
> +		*action |= (1 << maniptype);
> +out:
> +	return err;
> +}
> +
> +int nf_ct_nat(struct sk_buff *skb, struct nf_conn *ct,
> +	      enum ip_conntrack_info ctinfo, int *action,
> +	      const struct nf_nat_range2 *range, bool commit)
> +{
> +	enum nf_nat_manip_type maniptype;
> +	int err, ct_action = *action;
> +
> +	*action = 0;
> +
> +	/* Add NAT extension if not confirmed yet. */
> +	if (!nf_ct_is_confirmed(ct) && !nf_ct_nat_ext_add(ct))
> +		return NF_ACCEPT;   /* Can't NAT. */
> +
> +	if (ctinfo != IP_CT_NEW && (ct->status & IPS_NAT_MASK) &&
> +	    (ctinfo != IP_CT_RELATED || commit)) {
> +		/* NAT an established or related connection like before. */
> +		if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY)
> +			/* This is the REPLY direction for a connection
> +			 * for which NAT was applied in the forward
> +			 * direction.  Do the reverse NAT.
> +			 */
> +			maniptype = ct->status & IPS_SRC_NAT
> +				? NF_NAT_MANIP_DST : NF_NAT_MANIP_SRC;
> +		else
> +			maniptype = ct->status & IPS_SRC_NAT
> +				? NF_NAT_MANIP_SRC : NF_NAT_MANIP_DST;
> +	} else if (ct_action & (1 << NF_NAT_MANIP_SRC)) {
> +		maniptype = NF_NAT_MANIP_SRC;
> +	} else if (ct_action & (1 << NF_NAT_MANIP_DST)) {
> +		maniptype = NF_NAT_MANIP_DST;
> +	} else {
> +		return NF_ACCEPT;
> +	}
> +
> +	err = nf_ct_nat_execute(skb, ct, ctinfo, action, range, maniptype);
> +	if (err == NF_ACCEPT && ct->status & IPS_DST_NAT) {
> +		if (ct->status & IPS_SRC_NAT) {
> +			if (maniptype == NF_NAT_MANIP_SRC)
> +				maniptype = NF_NAT_MANIP_DST;
> +			else
> +				maniptype = NF_NAT_MANIP_SRC;
> +
> +			err = nf_ct_nat_execute(skb, ct, ctinfo, action, range,
> +						maniptype);
> +		} else if (CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
> +			err = nf_ct_nat_execute(skb, ct, ctinfo, action, NULL,
> +						NF_NAT_MANIP_SRC);
> +		}
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(nf_ct_nat);

I'd suggest you move this code to nf_nat_ovs.c or such so we remember
these symbols are used by act_ct.c and ovs.