bpf: sockmap, fix transition through disconnect without close

It is possible (via shutdown()) for TCP socks to go trough TCP_CLOSE
state via tcp_disconnect() without actually calling tcp_close which
would then call our bpf_tcp_close() callback. Because of this a user
could disconnect a socket then put it in a LISTEN state which would
break our assumptions about sockets always being ESTABLISHED state.

To resolve this rely on the unhash hook, which is called in the
disconnect case, to remove the sock from the sockmap.
Reported-by: Eric Dumazet <edumazet@google.com>
Fixes: 1aa12bdf ("bpf: sockmap, add sock close() hook to remove socks")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/sockmap.c

@@ -132,6 +132,7 @@ struct smap_psock {
 	struct work_struct gc_work;
 
 	struct proto *sk_proto;
+	void (*save_unhash)(struct sock *sk);
 	void (*save_close)(struct sock *sk, long timeout);
 	void (*save_data_ready)(struct sock *sk);
 	void (*save_write_space)(struct sock *sk);
@@ -143,6 +144,7 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
 static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
 			    int offset, size_t size, int flags);
+static void bpf_tcp_unhash(struct sock *sk);
 static void bpf_tcp_close(struct sock *sk, long timeout);
 
 static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
@@ -184,6 +186,7 @@ static void build_protos(struct proto prot[SOCKMAP_NUM_CONFIGS],
 			 struct proto *base)
 {
 	prot[SOCKMAP_BASE]			= *base;
+	prot[SOCKMAP_BASE].unhash		= bpf_tcp_unhash;
 	prot[SOCKMAP_BASE].close		= bpf_tcp_close;
 	prot[SOCKMAP_BASE].recvmsg		= bpf_tcp_recvmsg;
 	prot[SOCKMAP_BASE].stream_memory_read	= bpf_tcp_stream_read;
@@ -217,6 +220,7 @@ static int bpf_tcp_init(struct sock *sk)
 		return -EBUSY;
 	}
 
+	psock->save_unhash = sk->sk_prot->unhash;
 	psock->save_close = sk->sk_prot->close;
 	psock->sk_proto = sk->sk_prot;
 
@@ -305,30 +309,12 @@ static struct smap_psock_map_entry *psock_map_pop(struct sock *sk,
 	return e;
 }
 
-static void bpf_tcp_close(struct sock *sk, long timeout)
+static void bpf_tcp_remove(struct sock *sk, struct smap_psock *psock)
 {
-	void (*close_fun)(struct sock *sk, long timeout);
 	struct smap_psock_map_entry *e;
 	struct sk_msg_buff *md, *mtmp;
-	struct smap_psock *psock;
 	struct sock *osk;
 
-	lock_sock(sk);
-	rcu_read_lock();
-	psock = smap_psock_sk(sk);
-	if (unlikely(!psock)) {
-		rcu_read_unlock();
-		release_sock(sk);
-		return sk->sk_prot->close(sk, timeout);
-	}
-
-	/* The psock may be destroyed anytime after exiting the RCU critial
-	 * section so by the time we use close_fun the psock may no longer
-	 * be valid. However, bpf_tcp_close is called with the sock lock
-	 * held so the close hook and sk are still valid.
-	 */
-	close_fun = psock->save_close;
-
 	if (psock->cork) {
 		free_start_sg(psock->sock, psock->cork, true);
 		kfree(psock->cork);
@@ -379,6 +365,42 @@ static void bpf_tcp_close(struct sock *sk, long timeout)
 		kfree(e);
 		e = psock_map_pop(sk, psock);
 	}
+}
+
+static void bpf_tcp_unhash(struct sock *sk)
+{
+	void (*unhash_fun)(struct sock *sk);
+	struct smap_psock *psock;
+
+	rcu_read_lock();
+	psock = smap_psock_sk(sk);
+	if (unlikely(!psock)) {
+		rcu_read_unlock();
+		if (sk->sk_prot->unhash)
+			sk->sk_prot->unhash(sk);
+		return;
+	}
+	unhash_fun = psock->save_unhash;
+	bpf_tcp_remove(sk, psock);
+	rcu_read_unlock();
+	unhash_fun(sk);
+}
+
+static void bpf_tcp_close(struct sock *sk, long timeout)
+{
+	void (*close_fun)(struct sock *sk, long timeout);
+	struct smap_psock *psock;
+
+	lock_sock(sk);
+	rcu_read_lock();
+	psock = smap_psock_sk(sk);
+	if (unlikely(!psock)) {
+		rcu_read_unlock();
+		release_sock(sk);
+		return sk->sk_prot->close(sk, timeout);
+	}
+	close_fun = psock->save_close;
+	bpf_tcp_remove(sk, psock);
 	rcu_read_unlock();
 	release_sock(sk);
 	close_fun(sk, timeout);