Move and rename nf_reject_fill_skb_dst from
ipv4/netfilter/nf_reject_ipv4 to ip_route_reply_fetch_dst in
ipv4/route.c so that it can be reused in the following patches by BPF
kfuncs.

Netfilter uses nf_ip_route that is almost a transparent wrapper around
ip_route_output_key so this patch inlines it.

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
---
 include/net/route.h                 |  1 +
 net/ipv4/netfilter/nf_reject_ipv4.c | 19 ++-----------------
 net/ipv4/route.c                    | 15 +++++++++++++++
 3 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/include/net/route.h b/include/net/route.h
index f90106f383c5..ec2466fd0bec 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -173,6 +173,7 @@ struct rtable *ip_route_output_flow(struct net *, struct flowi4 *flp,
 				    const struct sock *sk);
 struct dst_entry *ipv4_blackhole_route(struct net *net,
 				       struct dst_entry *dst_orig);
+int ip_route_reply_fetch_dst(struct sk_buff *skb);

 static inline struct rtable *ip_route_output_key(struct net *net, struct flowi4 *flp)
 {
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index fecf6621f679..2290451ed122 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -252,21 +252,6 @@ static void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *
 	nskb->csum_offset = offsetof(struct tcphdr, check);
 }

-static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
-{
-	struct dst_entry *dst = NULL;
-	struct flowi fl;
-
-	memset(&fl, 0, sizeof(struct flowi));
-	fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
-	nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
-	if (!dst)
-		return -1;
-
-	skb_dst_set(skb_in, dst);
-	return 0;
-}
-
 /* Send RST reply */
 void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 		   int hook)
@@ -279,7 +264,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 	if (!oth)
 		return;

-	if (!skb_dst(oldskb) && nf_reject_fill_skb_dst(oldskb) < 0)
+	if (!skb_dst(oldskb) && ip_route_reply_fetch_dst(oldskb) < 0)
 		return;

 	if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
@@ -352,7 +337,7 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
 	if (iph->frag_off & htons(IP_OFFSET))
 		return;

-	if (!skb_dst(skb_in) && nf_reject_fill_skb_dst(skb_in) < 0)
+	if (!skb_dst(skb_in) && ip_route_reply_fetch_dst(skb_in) < 0)
 		return;

 	if (skb_csum_unnecessary(skb_in) ||
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index bc1296f0ea69..7091ef936073 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2945,6 +2945,21 @@ struct rtable *ip_route_output_flow(struct net *net, struct flowi4 *flp4,
 }
 EXPORT_SYMBOL_GPL(ip_route_output_flow);

+int ip_route_reply_fetch_dst(struct sk_buff *skb)
+{
+	struct rtable *rt;
+	struct flowi4 fl4 = {
+		.daddr = ip_hdr(skb)->saddr
+	};
+
+	rt = ip_route_output_key(dev_net(skb->dev), &fl4);
+	if (IS_ERR(rt))
+		return PTR_ERR(rt);
+	skb_dst_set(skb, &rt->dst);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ip_route_reply_fetch_dst);
+
 /* called with rcu_read_lock held */
 static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
 			struct rtable *rt, u32 table_id, dscp_t dscp,
--
2.34.1