[PATCH 4.19 72/88] media: rc: uevent sysfs file races with rc_unregister_device()

Greg Kroah-Hartman
2020-09-08T18:31:06Z

From: Sean Young <sean@mess.org>

commit 4f0835d6677dc69263f90f976524cb92b257d9f4 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/media/rc/rc-main.c
+++ b/drivers/media/rc/rc-main.c
@@ -1568,25 +1568,25 @@ static void rc_dev_release(struct 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;
}

/*
@@ -1970,14 +1970,14 @@ void rc_unregister_device(struct rc_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.