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

Greg Kroah-Hartman
2022-02-07T11:19:58Z

From: Matthias Kaehlcke <mka@chromium.org>

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@linaro.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220110104706.v6.2.Idde68b05b88d4a2e6e54766c653f3a6d9e419ce6@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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;