[PATCH 4.19 25/86] rpmsg: char: Fix race between the release of rpmsg_eptdev and cdev

[Greg Kroah-Hartman]

From: Matthias Kaehlcke <mka@xxxxxxxxxxxx>

commit 7a534ae89e34e9b51acb5a63dd0f88308178b46a upstream.

struct rpmsg_eptdev contains a struct cdev. The current code frees
the rpmsg_eptdev struct in rpmsg_eptdev_destroy(), but the cdev is
a managed object, therefore its release is not predictable and the
rpmsg_eptdev could be freed before the cdev is entirely released.

The cdev_device_add/del() API was created to address this issue
(see commit '233ed09d7fda ("chardev: add helper function to register
char devs with a struct device")'), use it instead of cdev add/del().

Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
Suggested-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Reviewed-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220110104706.v6.2.Idde68b05b88d4a2e6e54766c653f3a6d9e419ce6@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/rpmsg/rpmsg_char.c |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -92,7 +92,7 @@ static int rpmsg_eptdev_destroy(struct d
 	/* wake up any blocked readers */
 	wake_up_interruptible(&eptdev->readq);
 
-	device_del(&eptdev->dev);
+	cdev_device_del(&eptdev->cdev, &eptdev->dev);
 	put_device(&eptdev->dev);
 
 	return 0;
@@ -329,7 +329,6 @@ static void rpmsg_eptdev_release_device(
 
 	ida_simple_remove(&rpmsg_ept_ida, dev->id);
 	ida_simple_remove(&rpmsg_minor_ida, MINOR(eptdev->dev.devt));
-	cdev_del(&eptdev->cdev);
 	kfree(eptdev);
 }
 
@@ -374,19 +373,13 @@ static int rpmsg_eptdev_create(struct rp
 	dev->id = ret;
 	dev_set_name(dev, "rpmsg%d", ret);
 
-	ret = cdev_add(&eptdev->cdev, dev->devt, 1);
+	ret = cdev_device_add(&eptdev->cdev, &eptdev->dev);
 	if (ret)
 		goto free_ept_ida;
 
 	/* We can now rely on the release function for cleanup */
 	dev->release = rpmsg_eptdev_release_device;
 
-	ret = device_add(dev);
-	if (ret) {
-		dev_err(dev, "device_add failed: %d\n", ret);
-		put_device(dev);
-	}
-
 	return ret;
 
 free_ept_ida: