media: rc: uevent sysfs file races with rc_unregister_device()

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>

diff --git a/drivers/media/rc/rc-main.c b/drivers/media/rc/rc-main.c
index 7b53066..e1cda80 100644 (file)
--- 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.