ipv6: anycast: Unify two error paths in ipv6_sock_ac_join().

JIRA: https://issues.redhat.com/browse/RHEL-115325

commit 976fa9b
Author: Kuniyuki Iwashima <kuniyu@google.com>
Date:   Wed Jul 2 16:01:30 2025 -0700

    ipv6: anycast: Unify two error paths in ipv6_sock_ac_join().

    The next patch will replace __dev_get_by_index() and __dev_get_by_flags()
    to RCU + refcount version.

    Then, we will need to call dev_put() in some error paths.

    Let's unify two error paths to make the next patch cleaner.

    Note that we add READ_ONCE() for net->ipv6.devconf_all->forwarding
    and idev->conf.forwarding as we will drop RTNL that protects them.

    Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://patch.msgid.link/20250702230210.3115355-14-kuni1840@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/ipv6/anycast.c

@@ -67,12 +67,11 @@ static u32 inet6_acaddr_hash(const struct net *net,
 int ipv6_sock_ac_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
 {
 	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_ac_socklist *pac = NULL;
+	struct net *net = sock_net(sk);
 	struct net_device *dev = NULL;
 	struct inet6_dev *idev;
-	struct ipv6_ac_socklist *pac;
-	struct net *net = sock_net(sk);
-	int	ishost = !net->ipv6.devconf_all->forwarding;
-	int	err = 0;
+	int err = 0, ishost;
 
 	ASSERT_RTNL();
 
@@ -84,15 +83,22 @@ int ipv6_sock_ac_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
 	if (ifindex)
 		dev = __dev_get_by_index(net, ifindex);
 
-	if (ipv6_chk_addr_and_flags(net, addr, dev, true, 0, IFA_F_TENTATIVE))
-		return -EINVAL;
+	if (ipv6_chk_addr_and_flags(net, addr, dev, true, 0, IFA_F_TENTATIVE)) {
+		err = -EINVAL;
+		goto error;
+	}
 
 	pac = sock_kmalloc(sk, sizeof(struct ipv6_ac_socklist), GFP_KERNEL);
-	if (!pac)
-		return -ENOMEM;
+	if (!pac) {
+		err = -ENOMEM;
+		goto error;
+	}
+
 	pac->acl_next = NULL;
 	pac->acl_addr = *addr;
 
+	ishost = !READ_ONCE(net->ipv6.devconf_all->forwarding);
+
 	if (ifindex == 0) {
 		struct rt6_info *rt;
 
@@ -123,8 +129,9 @@ int ipv6_sock_ac_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
 			err = -EADDRNOTAVAIL;
 		goto error;
 	}
+
 	/* reset ishost, now that we have a specific device */
-	ishost = !idev->cnf.forwarding;
+	ishost = !READ_ONCE(idev->cnf.forwarding);
 
 	pac->acl_ifindex = dev->ifindex;