[PATCH V4 2/2] rpmsg: ctrl: Add lock to rpmsg_ctrldev_remove

[Deepak Kumar Singh <quic_deesin@quicinc.com>]

Call to rpmsg_ctrldev_ioctl() and rpmsg_ctrldev_remove() must be synchronized.
In present code rpmsg_ctrldev_remove() is not protected with lock, therefore
new char device creation can succeed through rpmsg_ctrldev_ioctl() call. At the
same time call to rpmsg_ctrldev_remove() funtion for ctrl device removal will
free associated rpdev device. As char device creation already succeeded, user
space is free to issue open() call which maps to rpmsg_create_ept() in kernel.
rpmsg_create_ept() function tries to reference rpdev which has already been
freed through rpmsg_ctrldev_remove(). Issue is predominantly seen in aggressive
reboot tests where rpmsg_ctrldev_ioctl() and rpmsg_ctrldev_remove() can race with
each other.

Adding lock in rpmsg_ctrldev_remove() avoids any new char device creation
throught rpmsg_ctrldev_ioctl() while remove call is already in progress.

Signed-off-by: Deepak Kumar Singh <quic_deesin@quicinc.com>
---
 drivers/rpmsg/rpmsg_ctrl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
index 107da70..4332538 100644
--- a/drivers/rpmsg/rpmsg_ctrl.c
+++ b/drivers/rpmsg/rpmsg_ctrl.c
@@ -194,10 +194,12 @@ static void rpmsg_ctrldev_remove(struct rpmsg_device *rpdev)
 	struct rpmsg_ctrldev *ctrldev = dev_get_drvdata(&rpdev->dev);
 	int ret;
 
+	mutex_lock(&ctrldev->ctrl_lock);
 	/* Destroy all endpoints */
 	ret = device_for_each_child(&ctrldev->dev, NULL, rpmsg_chrdev_eptdev_destroy);
 	if (ret)
 		dev_warn(&rpdev->dev, "failed to nuke endpoints: %d\n", ret);
+	mutex_unlock(&ctrldev->ctrl_lock);
 
 	cdev_device_del(&ctrldev->cdev, &ctrldev->dev);
 	put_device(&ctrldev->dev);
-- 
2.7.4