Merge branch 'vsock-virtio-fixes'

Stefano Garzarella says:

====================
vsock/virtio: several fixes in the .probe() and .remove()

During the review of "[PATCH] vsock/virtio: Initialize core virtio vsock
before registering the driver", Stefan pointed out some possible issues
in the .probe() and .remove() callbacks of the virtio-vsock driver.

This series tries to solve these issues:
- Patch 1 adds RCU critical sections to avoid use-after-free of
  'the_virtio_vsock' pointer.
- Patch 2 stops workers before to call vdev->config->reset(vdev) to
  be sure that no one is accessing the device.
- Patch 3 moves the works flush at the end of the .remove() to avoid
  use-after-free of 'vsock' object.

v2:
- Patch 1: use RCU to protect 'the_virtio_vsock' pointer
- Patch 2: no changes
- Patch 3: flush works only at the end of .remove()
- Removed patch 4 because virtqueue_detach_unused_buf() returns all the buffers
  allocated.

v1: https://patchwork.kernel.org/cover/10964733/
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/vmw_vsock/virtio_transport.c

@@ -38,6 +38,7 @@ struct virtio_vsock {
 	 * must be accessed with tx_lock held.
 	 */
 	struct mutex tx_lock;
+	bool tx_run;
 
 	struct work_struct send_pkt_work;
 	spinlock_t send_pkt_list_lock;
@@ -53,6 +54,7 @@ struct virtio_vsock {
 	 * must be accessed with rx_lock held.
 	 */
 	struct mutex rx_lock;
+	bool rx_run;
 	int rx_buf_nr;
 	int rx_buf_max_nr;
 
@@ -60,24 +62,28 @@ struct virtio_vsock {
 	 * vqs[VSOCK_VQ_EVENT] must be accessed with event_lock held.
 	 */
 	struct mutex event_lock;
+	bool event_run;
 	struct virtio_vsock_event event_list[8];
 
 	u32 guest_cid;
 };
 
-static struct virtio_vsock *virtio_vsock_get(void)
-{
-	return the_virtio_vsock;
-}
-
 static u32 virtio_transport_get_local_cid(void)
 {
-	struct virtio_vsock *vsock = virtio_vsock_get();
+	struct virtio_vsock *vsock;
+	u32 ret;
 
-	if (!vsock)
-		return VMADDR_CID_ANY;
+	rcu_read_lock();
+	vsock = rcu_dereference(the_virtio_vsock);
+	if (!vsock) {
+		ret = VMADDR_CID_ANY;
+		goto out_rcu;
+	}
 
-	return vsock->guest_cid;
+	ret = vsock->guest_cid;
+out_rcu:
+	rcu_read_unlock();
+	return ret;
 }
 
 static void virtio_transport_loopback_work(struct work_struct *work)
@@ -91,6 +97,10 @@ static void virtio_transport_loopback_work(struct work_struct *work)
 	spin_unlock_bh(&vsock->loopback_list_lock);
 
 	mutex_lock(&vsock->rx_lock);
+
+	if (!vsock->rx_run)
+		goto out;
+
 	while (!list_empty(&pkts)) {
 		struct virtio_vsock_pkt *pkt;
 
@@ -99,6 +109,7 @@ static void virtio_transport_loopback_work(struct work_struct *work)
 
 		virtio_transport_recv_pkt(pkt);
 	}
+out:
 	mutex_unlock(&vsock->rx_lock);
 }
 
@@ -127,6 +138,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 	mutex_lock(&vsock->tx_lock);
 
+	if (!vsock->tx_run)
+		goto out;
+
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
@@ -185,6 +199,7 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	if (added)
 		virtqueue_kick(vq);
 
+out:
 	mutex_unlock(&vsock->tx_lock);
 
 	if (restart_rx)
@@ -197,14 +212,18 @@ virtio_transport_send_pkt(struct virtio_vsock_pkt *pkt)
 	struct virtio_vsock *vsock;
 	int len = pkt->len;
 
-	vsock = virtio_vsock_get();
+	rcu_read_lock();
+	vsock = rcu_dereference(the_virtio_vsock);
 	if (!vsock) {
 		virtio_transport_free_pkt(pkt);
-		return -ENODEV;
+		len = -ENODEV;
+		goto out_rcu;
 	}
 
-	if (le64_to_cpu(pkt->hdr.dst_cid) == vsock->guest_cid)
-		return virtio_transport_send_pkt_loopback(vsock, pkt);
+	if (le64_to_cpu(pkt->hdr.dst_cid) == vsock->guest_cid) {
+		len = virtio_transport_send_pkt_loopback(vsock, pkt);
+		goto out_rcu;
+	}
 
 	if (pkt->reply)
 		atomic_inc(&vsock->queued_replies);
@@ -214,6 +233,9 @@ virtio_transport_send_pkt(struct virtio_vsock_pkt *pkt)
 	spin_unlock_bh(&vsock->send_pkt_list_lock);
 
 	queue_work(virtio_vsock_workqueue, &vsock->send_pkt_work);
+
+out_rcu:
+	rcu_read_unlock();
 	return len;
 }
 
@@ -222,12 +244,14 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
 {
 	struct virtio_vsock *vsock;
 	struct virtio_vsock_pkt *pkt, *n;
-	int cnt = 0;
+	int cnt = 0, ret;
 	LIST_HEAD(freeme);
 
-	vsock = virtio_vsock_get();
+	rcu_read_lock();
+	vsock = rcu_dereference(the_virtio_vsock);
 	if (!vsock) {
-		return -ENODEV;
+		ret = -ENODEV;
+		goto out_rcu;
 	}
 
 	spin_lock_bh(&vsock->send_pkt_list_lock);
@@ -255,7 +279,11 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
 			queue_work(virtio_vsock_workqueue, &vsock->rx_work);
 	}
 
-	return 0;
+	ret = 0;
+
+out_rcu:
+	rcu_read_unlock();
+	return ret;
 }
 
 static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
@@ -307,6 +335,10 @@ static void virtio_transport_tx_work(struct work_struct *work)
 
 	vq = vsock->vqs[VSOCK_VQ_TX];
 	mutex_lock(&vsock->tx_lock);
+
+	if (!vsock->tx_run)
+		goto out;
+
 	do {
 		struct virtio_vsock_pkt *pkt;
 		unsigned int len;
@@ -317,6 +349,8 @@ static void virtio_transport_tx_work(struct work_struct *work)
 			added = true;
 		}
 	} while (!virtqueue_enable_cb(vq));
+
+out:
 	mutex_unlock(&vsock->tx_lock);
 
 	if (added)
@@ -345,6 +379,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
 
 	mutex_lock(&vsock->rx_lock);
 
+	if (!vsock->rx_run)
+		goto out;
+
 	do {
 		virtqueue_disable_cb(vq);
 		for (;;) {
@@ -454,6 +491,9 @@ static void virtio_transport_event_work(struct work_struct *work)
 
 	mutex_lock(&vsock->event_lock);
 
+	if (!vsock->event_run)
+		goto out;
+
 	do {
 		struct virtio_vsock_event *event;
 		unsigned int len;
@@ -468,7 +508,7 @@ static void virtio_transport_event_work(struct work_struct *work)
 	} while (!virtqueue_enable_cb(vq));
 
 	virtqueue_kick(vsock->vqs[VSOCK_VQ_EVENT]);
-
+out:
 	mutex_unlock(&vsock->event_lock);
 }
 
@@ -590,8 +630,6 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
 	vsock->rx_buf_max_nr = 0;
 	atomic_set(&vsock->queued_replies, 0);
 
-	vdev->priv = vsock;
-	the_virtio_vsock = vsock;
 	mutex_init(&vsock->tx_lock);
 	mutex_init(&vsock->rx_lock);
 	mutex_init(&vsock->event_lock);
@@ -605,14 +643,23 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
 	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
 	INIT_WORK(&vsock->loopback_work, virtio_transport_loopback_work);
 
+	mutex_lock(&vsock->tx_lock);
+	vsock->tx_run = true;
+	mutex_unlock(&vsock->tx_lock);
+
 	mutex_lock(&vsock->rx_lock);
 	virtio_vsock_rx_fill(vsock);
+	vsock->rx_run = true;
 	mutex_unlock(&vsock->rx_lock);
 
 	mutex_lock(&vsock->event_lock);
 	virtio_vsock_event_fill(vsock);
+	vsock->event_run = true;
 	mutex_unlock(&vsock->event_lock);
 
+	vdev->priv = vsock;
+	rcu_assign_pointer(the_virtio_vsock, vsock);
+
 	mutex_unlock(&the_virtio_vsock_mutex);
 	return 0;
 
@@ -627,15 +674,33 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
 	struct virtio_vsock *vsock = vdev->priv;
 	struct virtio_vsock_pkt *pkt;
 
-	flush_work(&vsock->loopback_work);
-	flush_work(&vsock->rx_work);
-	flush_work(&vsock->tx_work);
-	flush_work(&vsock->event_work);
-	flush_work(&vsock->send_pkt_work);
+	mutex_lock(&the_virtio_vsock_mutex);
+
+	vdev->priv = NULL;
+	rcu_assign_pointer(the_virtio_vsock, NULL);
+	synchronize_rcu();
 
 	/* Reset all connected sockets when the device disappear */
 	vsock_for_each_connected_socket(virtio_vsock_reset_sock);
 
+	/* Stop all work handlers to make sure no one is accessing the device,
+	 * so we can safely call vdev->config->reset().
+	 */
+	mutex_lock(&vsock->rx_lock);
+	vsock->rx_run = false;
+	mutex_unlock(&vsock->rx_lock);
+
+	mutex_lock(&vsock->tx_lock);
+	vsock->tx_run = false;
+	mutex_unlock(&vsock->tx_lock);
+
+	mutex_lock(&vsock->event_lock);
+	vsock->event_run = false;
+	mutex_unlock(&vsock->event_lock);
+
+	/* Flush all device writes and interrupts, device will not use any
+	 * more buffers.
+	 */
 	vdev->config->reset(vdev);
 
 	mutex_lock(&vsock->rx_lock);
@@ -666,12 +731,20 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
 	}
 	spin_unlock_bh(&vsock->loopback_list_lock);
 
-	mutex_lock(&the_virtio_vsock_mutex);
-	the_virtio_vsock = NULL;
-	mutex_unlock(&the_virtio_vsock_mutex);
-
+	/* Delete virtqueues and flush outstanding callbacks if any */
 	vdev->config->del_vqs(vdev);
 
+	/* Other works can be queued before 'config->del_vqs()', so we flush
+	 * all works before to free the vsock object to avoid use after free.
+	 */
+	flush_work(&vsock->loopback_work);
+	flush_work(&vsock->rx_work);
+	flush_work(&vsock->tx_work);
+	flush_work(&vsock->event_work);
+	flush_work(&vsock->send_pkt_work);
+
+	mutex_unlock(&the_virtio_vsock_mutex);
+
 	kfree(vsock);
 }