uacce: Handle parent device removal or parent driver module rmmod

The uacce driver must deal with a possible removal of the parent device
or parent driver module rmmod at any time.

Although uacce_remove(), called on device removal and on driver unbind,
prevents future use of the uacce fops by removing the cdev, fops that
were called before that point may still be running.

Serialize uacce_fops_open() and uacce_remove() with uacce->mutex.
Serialize other fops against uacce_remove() with q->mutex.
Since we need to protect uacce_fops_poll() which gets called on the fast
path, replace uacce->queues_lock with q->mutex to improve scalability.
The other fops are only used during setup.

uacce_queue_is_valid(), checked under q->mutex or uacce->mutex, denotes
whether uacce_remove() has disabled all queues. If that is the case,
don't go any further since the parent device is being removed and
uacce->ops should not be called anymore.

Reported-by: Yang Shen <shenyang39@huawei.com>
Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20220701034843.7502-1-zhangfei.gao@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 87 insertions, 46 deletions

diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
index 281c54003edc..b70a013139c7 100644
--- a/drivers/misc/uacce/uacce.c
+++ b/drivers/misc/uacce/uacce.c
@@ -9,43 +9,38 @@
 
 static struct class *uacce_class;
 static dev_t uacce_devt;
-static DEFINE_MUTEX(uacce_mutex);
 static DEFINE_XARRAY_ALLOC(uacce_xa);
 
-static int uacce_start_queue(struct uacce_queue *q)
+/*
+ * If the parent driver or the device disappears, the queue state is invalid and
+ * ops are not usable anymore.
+ */
+static bool uacce_queue_is_valid(struct uacce_queue *q)
 {
-	int ret = 0;
+	return q->state == UACCE_Q_INIT || q->state == UACCE_Q_STARTED;
+}
 
-	mutex_lock(&uacce_mutex);
+static int uacce_start_queue(struct uacce_queue *q)
+{
+	int ret;
 
-	if (q->state != UACCE_Q_INIT) {
-		ret = -EINVAL;
-		goto out_with_lock;
-	}
+	if (q->state != UACCE_Q_INIT)
+		return -EINVAL;
 
 	if (q->uacce->ops->start_queue) {
 		ret = q->uacce->ops->start_queue(q);
 		if (ret < 0)
-			goto out_with_lock;
+			return ret;
 	}
 
 	q->state = UACCE_Q_STARTED;
-
-out_with_lock:
-	mutex_unlock(&uacce_mutex);
-
-	return ret;
+	return 0;
 }
 
 static int uacce_put_queue(struct uacce_queue *q)
 {
 	struct uacce_device *uacce = q->uacce;
 
-	mutex_lock(&uacce_mutex);
-
-	if (q->state == UACCE_Q_ZOMBIE)
-		goto out;
-
 	if ((q->state == UACCE_Q_STARTED) && uacce->ops->stop_queue)
 		uacce->ops->stop_queue(q);
 
@@ -54,8 +49,6 @@ static int uacce_put_queue(struct uacce_queue *q)
 		uacce->ops->put_queue(q);
 
 	q->state = UACCE_Q_ZOMBIE;
-out:
-	mutex_unlock(&uacce_mutex);
 
 	return 0;
 }
@@ -65,20 +58,36 @@ static long uacce_fops_unl_ioctl(struct file *filep,
 {
 	struct uacce_queue *q = filep->private_data;
 	struct uacce_device *uacce = q->uacce;
+	long ret = -ENXIO;
+
+	/*
+	 * uacce->ops->ioctl() may take the mmap_lock when copying arg to/from
+	 * user. Avoid a circular lock dependency with uacce_fops_mmap(), which
+	 * gets called with mmap_lock held, by taking uacce->mutex instead of
+	 * q->mutex. Doing this in uacce_fops_mmap() is not possible because
+	 * uacce_fops_open() calls iommu_sva_bind_device(), which takes
+	 * mmap_lock, while holding uacce->mutex.
+	 */
+	mutex_lock(&uacce->mutex);
+	if (!uacce_queue_is_valid(q))
+		goto out_unlock;
 
 	switch (cmd) {
 	case UACCE_CMD_START_Q:
-		return uacce_start_queue(q);
-
+		ret = uacce_start_queue(q);
+		break;
 	case UACCE_CMD_PUT_Q:
-		return uacce_put_queue(q);
-
+		ret = uacce_put_queue(q);
+		break;
 	default:
-		if (!uacce->ops->ioctl)
-			return -EINVAL;
-
-		return uacce->ops->ioctl(q, cmd, arg);
+		if (uacce->ops->ioctl)
+			ret = uacce->ops->ioctl(q, cmd, arg);
+		else
+			ret = -EINVAL;
 	}
+out_unlock:
+	mutex_unlock(&uacce->mutex);
+	return ret;
 }
 
 #ifdef CONFIG_COMPAT
@@ -136,6 +145,13 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
 	if (!q)
 		return -ENOMEM;
 
+	mutex_lock(&uacce->mutex);
+
+	if (!uacce->parent) {
+		ret = -EINVAL;
+		goto out_with_mem;
+	}
+
 	ret = uacce_bind_queue(uacce, q);
 	if (ret)
 		goto out_with_mem;
@@ -152,10 +168,9 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
 	filep->private_data = q;
 	uacce->inode = inode;
 	q->state = UACCE_Q_INIT;
-
-	mutex_lock(&uacce->queues_lock);
+	mutex_init(&q->mutex);
 	list_add(&q->list, &uacce->queues);
-	mutex_unlock(&uacce->queues_lock);
+	mutex_unlock(&uacce->mutex);
 
 	return 0;
 
@@ -163,18 +178,20 @@ out_with_bond:
 	uacce_unbind_queue(q);
 out_with_mem:
 	kfree(q);
+	mutex_unlock(&uacce->mutex);
 	return ret;
 }
 
 static int uacce_fops_release(struct inode *inode, struct file *filep)
 {
 	struct uacce_queue *q = filep->private_data;
+	struct uacce_device *uacce = q->uacce;
 
-	mutex_lock(&q->uacce->queues_lock);
-	list_del(&q->list);
-	mutex_unlock(&q->uacce->queues_lock);
+	mutex_lock(&uacce->mutex);
 	uacce_put_queue(q);
 	uacce_unbind_queue(q);
+	list_del(&q->list);
+	mutex_unlock(&uacce->mutex);
 	kfree(q);
 
 	return 0;
@@ -217,10 +234,9 @@ static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
 	vma->vm_private_data = q;
 	qfr->type = type;
 
-	mutex_lock(&uacce_mutex);
-
-	if (q->state != UACCE_Q_INIT && q->state != UACCE_Q_STARTED) {
-		ret = -EINVAL;
+	mutex_lock(&q->mutex);
+	if (!uacce_queue_is_valid(q)) {
+		ret = -ENXIO;
 		goto out_with_lock;
 	}
 
@@ -248,12 +264,12 @@ static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
 	}
 
 	q->qfrs[type] = qfr;
-	mutex_unlock(&uacce_mutex);
+	mutex_unlock(&q->mutex);
 
 	return ret;
 
 out_with_lock:
-	mutex_unlock(&uacce_mutex);
+	mutex_unlock(&q->mutex);
 	kfree(qfr);
 	return ret;
 }
@@ -262,12 +278,20 @@ static __poll_t uacce_fops_poll(struct file *file, poll_table *wait)
 {
 	struct uacce_queue *q = file->private_data;
 	struct uacce_device *uacce = q->uacce;
+	__poll_t ret = 0;
+
+	mutex_lock(&q->mutex);
+	if (!uacce_queue_is_valid(q))
+		goto out_unlock;
 
 	poll_wait(file, &q->wait, wait);
+
 	if (uacce->ops->is_q_updated && uacce->ops->is_q_updated(q))
-		return EPOLLIN | EPOLLRDNORM;
+		ret = EPOLLIN | EPOLLRDNORM;
 
-	return 0;
+out_unlock:
+	mutex_unlock(&q->mutex);
+	return ret;
 }
 
 static const struct file_operations uacce_fops = {
@@ -450,7 +474,7 @@ struct uacce_device *uacce_alloc(struct device *parent,
 		goto err_with_uacce;
 
 	INIT_LIST_HEAD(&uacce->queues);
-	mutex_init(&uacce->queues_lock);
+	mutex_init(&uacce->mutex);
 	device_initialize(&uacce->dev);
 	uacce->dev.devt = MKDEV(MAJOR(uacce_devt), uacce->dev_id);
 	uacce->dev.class = uacce_class;
@@ -507,13 +531,23 @@ void uacce_remove(struct uacce_device *uacce)
 	if (uacce->inode)
 		unmap_mapping_range(uacce->inode->i_mapping, 0, 0, 1);
 
+	/*
+	 * uacce_fops_open() may be running concurrently, even after we remove
+	 * the cdev. Holding uacce->mutex ensures that open() does not obtain a
+	 * removed uacce device.
+	 */
+	mutex_lock(&uacce->mutex);
 	/* ensure no open queue remains */
-	mutex_lock(&uacce->queues_lock);
 	list_for_each_entry_safe(q, next_q, &uacce->queues, list) {
+		/*
+		 * Taking q->mutex ensures that fops do not use the defunct
+		 * uacce->ops after the queue is disabled.
+		 */
+		mutex_lock(&q->mutex);
 		uacce_put_queue(q);
+		mutex_unlock(&q->mutex);
 		uacce_unbind_queue(q);
 	}
-	mutex_unlock(&uacce->queues_lock);
 
 	/* disable sva now since no opened queues */
 	uacce_disable_sva(uacce);
@@ -521,6 +555,13 @@ void uacce_remove(struct uacce_device *uacce)
 	if (uacce->cdev)
 		cdev_device_del(uacce->cdev, &uacce->dev);
 	xa_erase(&uacce_xa, uacce->dev_id);
+	/*
+	 * uacce exists as long as there are open fds, but ops will be freed
+	 * now. Ensure that bugs cause NULL deref rather than use-after-free.
+	 */
+	uacce->ops = NULL;
+	uacce->parent = NULL;
+	mutex_unlock(&uacce->mutex);
 	put_device(&uacce->dev);
 }
 EXPORT_SYMBOL_GPL(uacce_remove);