ipv6: use inet->cork.fl.u.ip6 and np->final in ip6_datagram_dst_update()

Get rid of @FL6 and &final variables in ip6_datagram_dst_update().

Use instead inet->cork.fl.u.ip6 and np->final so that a stack canary
is no longer needed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260206173426.1638518-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/ipv6/datagram.c

@@ -72,12 +72,12 @@ static void ip6_datagram_flow_key_init(struct flowi6 *fl6,
 int ip6_datagram_dst_update(struct sock *sk, bool fix_sk_saddr)
 {
 	struct ip6_flowlabel *flowlabel = NULL;
-	struct in6_addr *final_p, final;
-	struct ipv6_txoptions *opt;
-	struct dst_entry *dst;
 	struct inet_sock *inet = inet_sk(sk);
 	struct ipv6_pinfo *np = inet6_sk(sk);
-	struct flowi6 fl6;
+	struct ipv6_txoptions *opt;
+	struct in6_addr *final_p;
+	struct dst_entry *dst;
+	struct flowi6 *fl6;
 	int err = 0;
 
 	if (inet6_test_bit(SNDFLOW, sk) &&
@@ -86,32 +86,33 @@ int ip6_datagram_dst_update(struct sock *sk, bool fix_sk_saddr)
 		if (IS_ERR(flowlabel))
 			return -EINVAL;
 	}
-	ip6_datagram_flow_key_init(&fl6, sk);
+	fl6 = &inet_sk(sk)->cork.fl.u.ip6;
+	ip6_datagram_flow_key_init(fl6, sk);
 
 	rcu_read_lock();
 	opt = flowlabel ? flowlabel->opt : rcu_dereference(np->opt);
-	final_p = fl6_update_dst(&fl6, opt, &final);
+	final_p = fl6_update_dst(fl6, opt, &np->final);
 	rcu_read_unlock();
 
-	dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
+	dst = ip6_dst_lookup_flow(sock_net(sk), sk, fl6, final_p);
 	if (IS_ERR(dst)) {
 		err = PTR_ERR(dst);
 		goto out;
 	}
 
 	if (fix_sk_saddr) {
 		if (ipv6_addr_any(&np->saddr))
-			np->saddr = fl6.saddr;
+			np->saddr = fl6->saddr;
 
 		if (ipv6_addr_any(&sk->sk_v6_rcv_saddr)) {
-			sk->sk_v6_rcv_saddr = fl6.saddr;
+			sk->sk_v6_rcv_saddr = fl6->saddr;
 			inet->inet_rcv_saddr = LOOPBACK4_IPV6;
 			if (sk->sk_prot->rehash)
 				sk->sk_prot->rehash(sk);
 		}
 	}
 
-	ip6_sk_dst_store_flow(sk, dst, &fl6);
+	ip6_sk_dst_store_flow(sk, dst, fl6);
 
 out:
 	fl6_sock_release(flowlabel);