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Subject: media: rc: uevent sysfs file races with rc_unregister_device() Author: Sean Young sean@mess.org Date: Sat Aug 8 13:19:12 2020 +0200

Only report uevent file contents if device still registered, else we might read freed memory.

Reported-by: syzbot+ceef16277388d6f24898@syzkaller.appspotmail.com Cc: Hillf Danton hdanton@sina.com Cc: stable@vger.kernel.org # 4.16+ Signed-off-by: Sean Young sean@mess.org Signed-off-by: Mauro Carvalho Chehab mchehab+huawei@kernel.org

drivers/media/rc/rc-main.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-)

---

diff --git a/drivers/media/rc/rc-main.c b/drivers/media/rc/rc-main.c index 7b53066d9d07..e1cda80a4b25 100644 --- a/drivers/media/rc/rc-main.c +++ b/drivers/media/rc/rc-main.c @@ -1601,25 +1601,25 @@ static void rc_dev_release(struct device *device) kfree(dev); }

-#define ADD_HOTPLUG_VAR(fmt, val...) \ - do { \ - int err = add_uevent_var(env, fmt, val); \ - if (err) \ - return err; \ - } while (0) - static int rc_dev_uevent(struct device *device, struct kobj_uevent_env *env) { struct rc_dev *dev = to_rc_dev(device); + int ret = 0;

- if (dev->rc_map.name) - ADD_HOTPLUG_VAR("NAME=%s", dev->rc_map.name); - if (dev->driver_name) - ADD_HOTPLUG_VAR("DRV_NAME=%s", dev->driver_name); - if (dev->device_name) - ADD_HOTPLUG_VAR("DEV_NAME=%s", dev->device_name); + mutex_lock(&dev->lock);

- return 0; + if (!dev->registered) + ret = -ENODEV; + if (ret == 0 && dev->rc_map.name) + ret = add_uevent_var(env, "NAME=%s", dev->rc_map.name); + if (ret == 0 && dev->driver_name) + ret = add_uevent_var(env, "DRV_NAME=%s", dev->driver_name); + if (ret == 0 && dev->device_name) + ret = add_uevent_var(env, "DEV_NAME=%s", dev->device_name); + + mutex_unlock(&dev->lock); + + return ret; }

/* @@ -2011,14 +2011,14 @@ void rc_unregister_device(struct rc_dev *dev) del_timer_sync(&dev->timer_keyup); del_timer_sync(&dev->timer_repeat);

- rc_free_rx_device(dev); - mutex_lock(&dev->lock); if (dev->users && dev->close) dev->close(dev); dev->registered = false; mutex_unlock(&dev->lock);

+ rc_free_rx_device(dev); + /* * lirc device should be freed with dev->registered = false, so * that userspace polling will get notified.