bpf: Fix use-after-free of sockmap

net/core/skmsg.c

@@ -655,6 +655,14 @@ static void sk_psock_backlog(struct work_struct *work)
 	bool ingress;
 	int ret;
 
+	/* Increment the psock refcnt to synchronize with close(fd) path in
+	 * sock_map_close(), ensuring we wait for backlog thread completion
+	 * before sk_socket freed. If refcnt increment fails, it indicates
+	 * sock_map_close() completed with sk_socket potentially already freed.
+	 */
+	if (!sk_psock_get(psock->sk))
+		return;
+
 	mutex_lock(&psock->work_mutex);
 	if (unlikely(state->len)) {
 		len = state->len;
@@ -702,6 +710,7 @@ static void sk_psock_backlog(struct work_struct *work)
 	}
 end:
 	mutex_unlock(&psock->work_mutex);
+	sk_psock_put(psock->sk, psock);
 }
 
 struct sk_psock *sk_psock_init(struct sock *sk, int node)
@@ -1222,17 +1231,24 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 
 static void sk_psock_verdict_data_ready(struct sock *sk)
 {
-	struct socket *sock = sk->sk_socket;
+	struct socket *sock;
 	const struct proto_ops *ops;
 	int copied;
 
 	trace_sk_data_ready(sk);
 
-	if (unlikely(!sock))
+	rcu_read_lock();
+	sock = sk->sk_socket;
+	if (unlikely(!sock)) {
+		rcu_read_unlock();
 		return;
+	}
 	ops = READ_ONCE(sock->ops);
-	if (!ops || !ops->read_skb)
+	if (!ops || !ops->read_skb) {
+		rcu_read_unlock();
 		return;
+	}
+	rcu_read_unlock();
 	copied = ops->read_skb(sk, sk_psock_verdict_recv);
 	if (copied >= 0) {
 		struct sk_psock *psock;

tools/testing/selftests/bpf/prog_tests/socket_helpers.h

@@ -313,11 +313,22 @@ static inline int recv_timeout(int fd, void *buf, size_t len, int flags,
 
 static inline int create_pair(int family, int sotype, int *p0, int *p1)
 {
-	__close_fd int s, c = -1, p = -1;
+	__close_fd int s = -1, c = -1, p = -1;
 	struct sockaddr_storage addr;
 	socklen_t len = sizeof(addr);
 	int err;
 
+	if (family == AF_UNIX) {
+		int fds[2];
+
+		err = socketpair(family, sotype, 0, fds);
+		if (!err) {
+			*p0 = fds[0];
+			*p1 = fds[1];
+		}
+		return err;
+	}
+
 	s = socket_loopback(family, sotype);
 	if (s < 0)
 		return s;

tools/testing/selftests/bpf/prog_tests/sockmap_basic.c

@@ -1042,6 +1042,59 @@ static void test_sockmap_vsock_unconnected(void)
 	xclose(map);
 }
 
+void *close_thread(void *arg)
+{
+	int *fd = (int *)arg;
+
+	sleep(1);
+	close(*fd);
+	*fd = -1;
+	return NULL;
+}
+
+void test_sockmap_with_close_on_write(int family, int sotype)
+{
+	struct test_sockmap_pass_prog *skel;
+	int err, map, verdict;
+	pthread_t tid;
+	int zero = 0;
+	int c = -1, p = -1;
+
+	skel = test_sockmap_pass_prog__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	verdict = bpf_program__fd(skel->progs.prog_skb_verdict);
+	map = bpf_map__fd(skel->maps.sock_map_rx);
+
+	err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
+	if (!ASSERT_OK(err, "bpf_prog_attach"))
+		goto out;
+
+	err = create_pair(family, sotype, &c, &p);
+	if (!ASSERT_OK(err, "create_pair"))
+		goto out;
+
+	err = bpf_map_update_elem(map, &zero, &p, BPF_ANY);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	err = pthread_create(&tid, 0, close_thread, &p);
+	if (!ASSERT_OK(err, "pthread_create"))
+		goto out;
+
+	while (p > 0)
+		send(c, "a", 1, MSG_NOSIGNAL);
+
+	pthread_join(tid, NULL);
+out:
+	if (c > 0)
+		close(c);
+	if (p > 0)
+		close(p);
+	test_sockmap_pass_prog__destroy(skel);
+}
+
 void test_sockmap_basic(void)
 {
 	if (test__start_subtest("sockmap create_update_free"))
@@ -1108,4 +1161,11 @@ void test_sockmap_basic(void)
 		test_sockmap_skb_verdict_vsock_poll();
 	if (test__start_subtest("sockmap vsock unconnected"))
 		test_sockmap_vsock_unconnected();
+	if (test__start_subtest("sockmap with write on close")) {
+		test_sockmap_with_close_on_write(AF_UNIX, SOCK_STREAM);
+		test_sockmap_with_close_on_write(AF_UNIX, SOCK_DGRAM);
+		test_sockmap_with_close_on_write(AF_INET, SOCK_STREAM);
+		test_sockmap_with_close_on_write(AF_INET, SOCK_DGRAM);
+		test_sockmap_with_close_on_write(AF_VSOCK, SOCK_STREAM);
+	}
 }