diff --git a/net/can/isotp.c b/net/can/isotp.c
index 02cbcb2ecf0dbc58f458fd6127044113e4a368ba..d2a430b6a13bd2974adf02be1fe14e1886db7439 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -56,6 +56,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
+#include <linux/spinlock.h>
 #include <linux/hrtimer.h>
 #include <linux/wait.h>
 #include <linux/uio.h>
@@ -145,6 +146,7 @@ struct isotp_sock {
 	struct tpcon rx, tx;
 	struct list_head notifier;
 	wait_queue_head_t wait;
+	spinlock_t rx_lock; /* protect single thread state machine */
 };
 
 static LIST_HEAD(isotp_notifier_list);
@@ -615,11 +617,17 @@ static void isotp_rcv(struct sk_buff *skb, void *data)
 
 	n_pci_type = cf->data[ae] & 0xF0;
 
+	/* Make sure the state changes and data structures stay consistent at
+	 * CAN frame reception time. This locking is not needed in real world
+	 * use cases but the inconsistency can be triggered with syzkaller.
+	 */
+	spin_lock(&so->rx_lock);
+
 	if (so->opt.flags & CAN_ISOTP_HALF_DUPLEX) {
 		/* check rx/tx path half duplex expectations */
 		if ((so->tx.state != ISOTP_IDLE && n_pci_type != N_PCI_FC) ||
 		    (so->rx.state != ISOTP_IDLE && n_pci_type == N_PCI_FC))
-			return;
+			goto out_unlock;
 	}
 
 	switch (n_pci_type) {
@@ -668,6 +676,9 @@ static void isotp_rcv(struct sk_buff *skb, void *data)
 		isotp_rcv_cf(sk, cf, ae, skb);
 		break;
 	}
+
+out_unlock:
+	spin_unlock(&so->rx_lock);
 }
 
 static void isotp_fill_dataframe(struct canfd_frame *cf, struct isotp_sock *so,
@@ -876,7 +887,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 
 	if (!size || size > MAX_MSG_LENGTH) {
 		err = -EINVAL;
-		goto err_out;
+		goto err_out_drop;
 	}
 
 	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
@@ -886,24 +897,24 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if ((so->opt.flags & CAN_ISOTP_SF_BROADCAST) &&
 	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off)) {
 		err = -EINVAL;
-		goto err_out;
+		goto err_out_drop;
 	}
 
 	err = memcpy_from_msg(so->tx.buf, msg, size);
 	if (err < 0)
-		goto err_out;
+		goto err_out_drop;
 
 	dev = dev_get_by_index(sock_net(sk), so->ifindex);
 	if (!dev) {
 		err = -ENXIO;
-		goto err_out;
+		goto err_out_drop;
 	}
 
 	skb = sock_alloc_send_skb(sk, so->ll.mtu + sizeof(struct can_skb_priv),
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!skb) {
 		dev_put(dev);
-		goto err_out;
+		goto err_out_drop;
 	}
 
 	can_skb_reserve(skb);
@@ -965,7 +976,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (err) {
 		pr_notice_once("can-isotp: %s: can_send_ret %pe\n",
 			       __func__, ERR_PTR(err));
-		goto err_out;
+		goto err_out_drop;
 	}
 
 	if (wait_tx_done) {
@@ -978,6 +989,9 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 
 	return size;
 
+err_out_drop:
+	/* drop this PDU and unlock a potential wait queue */
+	old_state = ISOTP_IDLE;
 err_out:
 	so->tx.state = old_state;
 	if (so->tx.state == ISOTP_IDLE)
@@ -1444,6 +1458,7 @@ static int isotp_init(struct sock *sk)
 	so->txtimer.function = isotp_tx_timer_handler;
 
 	init_waitqueue_head(&so->wait);
+	spin_lock_init(&so->rx_lock);
 
 	spin_lock(&isotp_notifier_lock);
 	list_add_tail(&so->notifier, &isotp_notifier_list);