net: ipv6: fix dst refleaks in rpl, seg6 and ioam6 lwtunnels

dst_cache_get() gives us a reference, we need to release it.

Discovered by the ioam6.sh test, kmemleak was recently fixed
to catch per-cpu memory leaks.

Fixes: 985ec6f ("net: ipv6: rpl_iptunnel: mitigate 2-realloc issue")
Fixes: 40475b6 ("net: ipv6: seg6_iptunnel: mitigate 2-realloc issue")
Fixes: dce5251 ("net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue")
Reviewed-by: Justin Iurman <justin.iurman@uliege.be>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250130031519.2716843-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/ioam6_iptunnel.c

@@ -336,7 +336,7 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb,
 
 static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-	struct dst_entry *dst = skb_dst(skb), *cache_dst;
+	struct dst_entry *dst = skb_dst(skb), *cache_dst = NULL;
 	struct in6_addr orig_daddr;
 	struct ioam6_lwt *ilwt;
 	int err = -EINVAL;
@@ -407,7 +407,6 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 		cache_dst = ip6_route_output(net, NULL, &fl6);
 		if (cache_dst->error) {
 			err = cache_dst->error;
-			dst_release(cache_dst);
 			goto drop;
 		}
 
@@ -426,8 +425,10 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 		return dst_output(net, sk, skb);
 	}
 out:
+	dst_release(cache_dst);
 	return dst->lwtstate->orig_output(net, sk, skb);
 drop:
+	dst_release(cache_dst);
 	kfree_skb(skb);
 	return err;
 }

net/ipv6/rpl_iptunnel.c

@@ -232,7 +232,6 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 		dst = ip6_route_output(net, NULL, &fl6);
 		if (dst->error) {
 			err = dst->error;
-			dst_release(dst);
 			goto drop;
 		}
 
@@ -251,6 +250,7 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 	return dst_output(net, sk, skb);
 
 drop:
+	dst_release(dst);
 	kfree_skb(skb);
 	return err;
 }
@@ -269,8 +269,10 @@ static int rpl_input(struct sk_buff *skb)
 	local_bh_enable();
 
 	err = rpl_do_srh(skb, rlwt, dst);
-	if (unlikely(err))
+	if (unlikely(err)) {
+		dst_release(dst);
 		goto drop;
+	}
 
 	if (!dst) {
 		ip6_route_input(skb);

net/ipv6/seg6_iptunnel.c

@@ -482,8 +482,10 @@ static int seg6_input_core(struct net *net, struct sock *sk,
 	local_bh_enable();
 
 	err = seg6_do_srh(skb, dst);
-	if (unlikely(err))
+	if (unlikely(err)) {
+		dst_release(dst);
 		goto drop;
+	}
 
 	if (!dst) {
 		ip6_route_input(skb);
@@ -571,7 +573,6 @@ static int seg6_output_core(struct net *net, struct sock *sk,
 		dst = ip6_route_output(net, NULL, &fl6);
 		if (dst->error) {
 			err = dst->error;
-			dst_release(dst);
 			goto drop;
 		}
 
@@ -593,6 +594,7 @@ static int seg6_output_core(struct net *net, struct sock *sk,
 
 	return dst_output(net, sk, skb);
 drop:
+	dst_release(dst);
 	kfree_skb(skb);
 	return err;
 }