vsock: keep poll shutdown state consistent

vsock_poll() reads vsk->peer_shutdown before taking the socket lock
to set EPOLLHUP and EPOLLRDHUP, then reads it again after taking
the lock to report EOF readability. A shutdown packet can update
peer_shutdown while poll is waiting for the lock, so one poll invocation
can report EOF readability without the corresponding HUP/RDHUP bits.

For connectible sockets, take one peer_shutdown snapshot after
lock_sock() and use it for all peer-shutdown-derived poll bits. For
datagram sockets, which do not take lock_sock() in poll(), take one
lockless READ_ONCE() snapshot and pair it with WRITE_ONCE() on the
writer side.

This keeps the peer-shutdown-derived bits internally consistent for each
poll pass.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Signed-off-by: Ziyu Zhang <ziyuzhang201@gmail.com>
Link: https://patch.msgid.link/20260519165636.62542-1-ziyuzhang201@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 52 insertions, 28 deletions

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 44037b066a5f..2ce1063d4a67 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -642,7 +642,7 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
 		 */
 		sock_reset_flag(sk, SOCK_DONE);
 		sk->sk_state = TCP_CLOSE;
-		vsk->peer_shutdown = 0;
+		WRITE_ONCE(vsk->peer_shutdown, 0);
 	}
 
 	if (sk->sk_type == SOCK_SEQPACKET) {
@@ -933,7 +933,7 @@ static struct sock *__vsock_create(struct net *net,
 	vsk->rejected = false;
 	vsk->sent_request = false;
 	vsk->ignore_connecting_rst = false;
-	vsk->peer_shutdown = 0;
+	WRITE_ONCE(vsk->peer_shutdown, 0);
 	INIT_DELAYED_WORK(&vsk->connect_work, vsock_connect_timeout);
 	INIT_DELAYED_WORK(&vsk->pending_work, vsock_pending_work);
 
@@ -1241,6 +1241,25 @@ out:
 	return err;
 }
 
+static __poll_t vsock_poll_shutdown(struct sock *sk, u32 peer_shutdown)
+{
+	__poll_t mask = 0;
+
+	/* INET sockets treat local write shutdown and peer write shutdown as a
+	 * case of EPOLLHUP set.
+	 */
+	if (sk->sk_shutdown == SHUTDOWN_MASK ||
+	    ((sk->sk_shutdown & SEND_SHUTDOWN) &&
+	     (peer_shutdown & SEND_SHUTDOWN)))
+		mask |= EPOLLHUP;
+
+	if (sk->sk_shutdown & RCV_SHUTDOWN ||
+	    peer_shutdown & SEND_SHUTDOWN)
+		mask |= EPOLLRDHUP;
+
+	return mask;
+}
+
 static __poll_t vsock_poll(struct file *file, struct socket *sock,
 			       poll_table *wait)
 {
@@ -1258,24 +1277,17 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
 		/* Signify that there has been an error on this socket. */
 		mask |= EPOLLERR;
 
-	/* INET sockets treat local write shutdown and peer write shutdown as a
-	 * case of EPOLLHUP set.
-	 */
-	if ((sk->sk_shutdown == SHUTDOWN_MASK) ||
-	    ((sk->sk_shutdown & SEND_SHUTDOWN) &&
-	     (vsk->peer_shutdown & SEND_SHUTDOWN))) {
-		mask |= EPOLLHUP;
-	}
-
-	if (sk->sk_shutdown & RCV_SHUTDOWN ||
-	    vsk->peer_shutdown & SEND_SHUTDOWN) {
-		mask |= EPOLLRDHUP;
-	}
-
 	if (sk_is_readable(sk))
 		mask |= EPOLLIN | EPOLLRDNORM;
 
 	if (sock->type == SOCK_DGRAM) {
+		u32 peer_shutdown = READ_ONCE(vsk->peer_shutdown);
+
+		/* DGRAM sockets do not take lock_sock() in poll(), so use one
+		 * lockless snapshot for all shutdown-derived mask bits.
+		 */
+		mask |= vsock_poll_shutdown(sk, peer_shutdown);
+
 		/* For datagram sockets we can read if there is something in
 		 * the queue and write as long as the socket isn't shutdown for
 		 * sending.
@@ -1290,6 +1302,7 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
 
 	} else if (sock_type_connectible(sk->sk_type)) {
 		const struct vsock_transport *transport;
+		u32 peer_shutdown;
 
 		lock_sock(sk);
 
@@ -1322,8 +1335,10 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
 		 * terminated should also be considered read, and we check the
 		 * shutdown flag for that.
 		 */
+		peer_shutdown = READ_ONCE(vsk->peer_shutdown);
+		mask |= vsock_poll_shutdown(sk, peer_shutdown);
 		if (sk->sk_shutdown & RCV_SHUTDOWN ||
-		    vsk->peer_shutdown & SEND_SHUTDOWN) {
+		    peer_shutdown & SEND_SHUTDOWN) {
 			mask |= EPOLLIN | EPOLLRDNORM;
 		}
 
diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 7a8963595bf9..b3394946b2ed 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -264,7 +264,7 @@ static void hvs_do_close_lock_held(struct vsock_sock *vsk,
 	struct sock *sk = sk_vsock(vsk);
 
 	sock_set_flag(sk, SOCK_DONE);
-	vsk->peer_shutdown = SHUTDOWN_MASK;
+	WRITE_ONCE(vsk->peer_shutdown, SHUTDOWN_MASK);
 	if (vsock_stream_has_data(vsk) <= 0)
 		sk->sk_state = TCP_CLOSING;
 	sk->sk_state_change(sk);
@@ -593,7 +593,9 @@ static int hvs_update_recv_data(struct hvsock *hvs)
 		return -EIO;
 
 	if (payload_len == 0)
-		hvs->vsk->peer_shutdown |= SEND_SHUTDOWN;
+		WRITE_ONCE(hvs->vsk->peer_shutdown,
+			   READ_ONCE(hvs->vsk->peer_shutdown) |
+			   SEND_SHUTDOWN);
 
 	hvs->recv_data_len = payload_len;
 	hvs->recv_data_off = 0;
@@ -736,7 +738,8 @@ static s64 hvs_stream_has_data(struct vsock_sock *vsk)
 			return ret;
 		return hvs->recv_data_len;
 	case 0:
-		vsk->peer_shutdown |= SEND_SHUTDOWN;
+		WRITE_ONCE(vsk->peer_shutdown,
+			   READ_ONCE(vsk->peer_shutdown) | SEND_SHUTDOWN);
 		ret = 0;
 		break;
 	default: /* -1 */
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index df3b418e0392..d4d26fba9e37 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1228,7 +1228,7 @@ static void virtio_transport_do_close(struct vsock_sock *vsk,
 	struct sock *sk = sk_vsock(vsk);
 
 	sock_set_flag(sk, SOCK_DONE);
-	vsk->peer_shutdown = SHUTDOWN_MASK;
+	WRITE_ONCE(vsk->peer_shutdown, SHUTDOWN_MASK);
 	if (vsock_stream_has_data(vsk) <= 0)
 		sk->sk_state = TCP_CLOSING;
 	sk->sk_state_change(sk);
@@ -1431,12 +1431,15 @@ virtio_transport_recv_connected(struct sock *sk,
 	case VIRTIO_VSOCK_OP_CREDIT_UPDATE:
 		sk->sk_write_space(sk);
 		break;
-	case VIRTIO_VSOCK_OP_SHUTDOWN:
+	case VIRTIO_VSOCK_OP_SHUTDOWN: {
+		u32 peer_shutdown = READ_ONCE(vsk->peer_shutdown);
+
 		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SHUTDOWN_RCV)
-			vsk->peer_shutdown |= RCV_SHUTDOWN;
+			peer_shutdown |= RCV_SHUTDOWN;
 		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SHUTDOWN_SEND)
-			vsk->peer_shutdown |= SEND_SHUTDOWN;
-		if (vsk->peer_shutdown == SHUTDOWN_MASK) {
+			peer_shutdown |= SEND_SHUTDOWN;
+		WRITE_ONCE(vsk->peer_shutdown, peer_shutdown);
+		if (peer_shutdown == SHUTDOWN_MASK) {
 			if (vsock_stream_has_data(vsk) <= 0 && !sock_flag(sk, SOCK_DONE)) {
 				(void)virtio_transport_reset(vsk, NULL);
 				virtio_transport_do_close(vsk, true);
@@ -1451,6 +1454,7 @@ virtio_transport_recv_connected(struct sock *sk,
 		if (le32_to_cpu(virtio_vsock_hdr(skb)->flags))
 			sk->sk_state_change(sk);
 		break;
+	}
 	case VIRTIO_VSOCK_OP_RST:
 		virtio_transport_do_close(vsk, true);
 		break;
diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
index d2579380f51e..5c1ecd5bfdbc 100644
--- a/net/vmw_vsock/vmci_transport.c
+++ b/net/vmw_vsock/vmci_transport.c
@@ -819,7 +819,7 @@ static void vmci_transport_handle_detach(struct sock *sk)
 		/* On a detach the peer will not be sending or receiving
 		 * anymore.
 		 */
-		vsk->peer_shutdown = SHUTDOWN_MASK;
+		WRITE_ONCE(vsk->peer_shutdown, SHUTDOWN_MASK);
 
 		/* We should not be sending anymore since the peer won't be
 		 * there to receive, but we can still receive if there is data
@@ -1542,7 +1542,9 @@ static int vmci_transport_recv_connected(struct sock *sk,
 		if (pkt->u.mode) {
 			vsk = vsock_sk(sk);
 
-			vsk->peer_shutdown |= pkt->u.mode;
+			WRITE_ONCE(vsk->peer_shutdown,
+				   READ_ONCE(vsk->peer_shutdown) |
+				   pkt->u.mode);
 			sk->sk_state_change(sk);
 		}
 		break;
@@ -1559,7 +1561,7 @@ static int vmci_transport_recv_connected(struct sock *sk,
 		 * a clean shutdown.
 		 */
 		sock_set_flag(sk, SOCK_DONE);
-		vsk->peer_shutdown = SHUTDOWN_MASK;
+		WRITE_ONCE(vsk->peer_shutdown, SHUTDOWN_MASK);
 		if (vsock_stream_has_data(vsk) <= 0)
 			sk->sk_state = TCP_CLOSING;