net: move netfilter nf_reject6_fill_skb_dst to core ipv6

Move and rename nf_reject6_fill_skb_dst from
ipv6/netfilter/nf_reject_ipv6 to ip6_route_reply_fetch_dst in
ipv6/route.c so that it can be reused in the following patches by BPF
kfuncs.

Netfilter uses nf_ip6_route that is almost a transparent wrapper around
ip6_route_outputy so this patch inlines it.

Signed-off-by: Mahe Tardy <[email protected]>

Author: mtardy

include/net/ip6_route.h

@@ -93,6 +93,8 @@ static inline struct dst_entry *ip6_route_output(struct net *net,
 	return ip6_route_output_flags(net, sk, fl6, 0);
 }
 
+int ip6_route_reply_fetch_dst(struct sk_buff *skb);
+
 /* Only conditionally release dst if flags indicates
  * !RT6_LOOKUP_F_DST_NOREF or dst is in uncached_list.
  */

net/ipv6/netfilter/nf_reject_ipv6.c

@@ -250,21 +250,6 @@ void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
 }
 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
 
-static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
-{
-	struct dst_entry *dst = NULL;
-	struct flowi fl;
-
-	memset(&fl, 0, sizeof(struct flowi));
-	fl.u.ip6.daddr = ipv6_hdr(skb_in)->saddr;
-	nf_ip6_route(dev_net(skb_in->dev), &dst, &fl, false);
-	if (!dst)
-		return -1;
-
-	skb_dst_set(skb_in, dst);
-	return 0;
-}
-
 void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 		    int hook)
 {
@@ -398,7 +383,7 @@ void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
 		skb_in->dev = net->loopback_dev;
 
 	if ((hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_INGRESS) &&
-	    nf_reject6_fill_skb_dst(skb_in) < 0)
+	    ip6_route_reply_fetch_dst(skb_in) < 0)
 		return;
 
 	icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);

net/ipv6/route.c

@@ -2705,6 +2705,24 @@ struct dst_entry *ip6_route_output_flags(struct net *net,
 }
 EXPORT_SYMBOL_GPL(ip6_route_output_flags);
 
+int ip6_route_reply_fetch_dst(struct sk_buff *skb)
+{
+	struct dst_entry *result;
+	struct flowi6 fl = {
+		.daddr = ipv6_hdr(skb)->saddr
+	};
+	int err;
+
+	result = ip6_route_output(dev_net(skb->dev), NULL, &fl);
+	err = result->error;
+	if (err)
+		dst_release(result);
+	else
+		skb_dst_set(skb, result);
+	return err;
+}
+EXPORT_SYMBOL_GPL(ip6_route_reply_fetch_dst);
+
 struct dst_entry *ip6_blackhole_route(struct net *net, struct dst_entry *dst_orig)
 {
 	struct rt6_info *rt, *ort = dst_rt6_info(dst_orig);