tcp: Fix Use-After-Free in tcp_ao_connect_init

Since call_rcu, which is called in the hlist_for_each_entry_rcu traversal
of tcp_ao_connect_init, is not part of the RCU read critical section, it
is possible that the RCU grace period will pass during the traversal and
the key will be free.

To prevent this, it should be changed to hlist_for_each_entry_safe.

Fixes: 7c2ffaf ("net/tcp: Calculate TCP-AO traffic keys")
Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://lore.kernel.org/r/ZiYu9NJ/ClR8uSkH@v4bel-B760M-AORUS-ELITE-AX
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_ao.c

@@ -1068,6 +1068,7 @@ void tcp_ao_connect_init(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_ao_info *ao_info;
+	struct hlist_node *next;
 	union tcp_ao_addr *addr;
 	struct tcp_ao_key *key;
 	int family, l3index;
@@ -1090,7 +1091,7 @@ void tcp_ao_connect_init(struct sock *sk)
 	l3index = l3mdev_master_ifindex_by_index(sock_net(sk),
 						 sk->sk_bound_dev_if);
 
-	hlist_for_each_entry_rcu(key, &ao_info->head, node) {
+	hlist_for_each_entry_safe(key, next, &ao_info->head, node) {
 		if (!tcp_ao_key_cmp(key, l3index, addr, key->prefixlen, family, -1, -1))
 			continue;