bpf, sockmap: Don't let sock_map_{close,destroy,unhash} call itself

sock_map proto callbacks should never call themselves by design. Protect
against bugs like [1] and break out of the recursive loop to avoid a stack
overflow in favor of a resource leak.

[1] https://lore.kernel.org/all/00000000000073b14905ef2e7401@google.com/Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20230113-sockmap-fix-v2-1-1e0ee7ac2f90@cloudflare.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/sock_map.c

@@ -1569,14 +1569,15 @@ void sock_map_unhash(struct sock *sk)
 	psock = sk_psock(sk);
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
-		if (sk->sk_prot->unhash)
-			sk->sk_prot->unhash(sk);
-		return;
-	}
-
+		saved_unhash = READ_ONCE(sk->sk_prot)->unhash;
+	} else {
 		saved_unhash = psock->saved_unhash;
 		sock_map_remove_links(sk, psock);
 		rcu_read_unlock();
+	}
+	if (WARN_ON_ONCE(saved_unhash == sock_map_unhash))
+		return;
+	if (saved_unhash)
 		saved_unhash(sk);
 }
 EXPORT_SYMBOL_GPL(sock_map_unhash);
@@ -1590,16 +1591,17 @@ void sock_map_destroy(struct sock *sk)
 	psock = sk_psock_get(sk);
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
-		if (sk->sk_prot->destroy)
-			sk->sk_prot->destroy(sk);
-		return;
-	}
-
+		saved_destroy = READ_ONCE(sk->sk_prot)->destroy;
+	} else {
 		saved_destroy = psock->saved_destroy;
 		sock_map_remove_links(sk, psock);
 		rcu_read_unlock();
 		sk_psock_stop(psock);
 		sk_psock_put(sk, psock);
+	}
+	if (WARN_ON_ONCE(saved_destroy == sock_map_destroy))
+		return;
+	if (saved_destroy)
 		saved_destroy(sk);
 }
 EXPORT_SYMBOL_GPL(sock_map_destroy);
@@ -1615,9 +1617,8 @@ void sock_map_close(struct sock *sk, long timeout)
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
 		release_sock(sk);
-		return sk->sk_prot->close(sk, timeout);
-	}
-
+		saved_close = READ_ONCE(sk->sk_prot)->close;
+	} else {
 		saved_close = psock->saved_close;
 		sock_map_remove_links(sk, psock);
 		rcu_read_unlock();
@@ -1625,6 +1626,12 @@ void sock_map_close(struct sock *sk, long timeout)
 		release_sock(sk);
 		cancel_work_sync(&psock->work);
 		sk_psock_put(sk, psock);
+	}
+	/* Make sure we do not recurse. This is a bug.
+	 * Leak the socket instead of crashing on a stack overflow.
+	 */
+	if (WARN_ON_ONCE(saved_close == sock_map_close))
+		return;
 	saved_close(sk, timeout);
 }
 EXPORT_SYMBOL_GPL(sock_map_close);