Lightbulb Successfully Write Path to uevent_helper But Can NOT Root!

I found a world wide write vulnerability in a new model of Huawei. (Android 4.4.2)
And successfully write a path "/data/local/tmp/" to /sys/kernel/uevent_helper

Here is the problem, after I write the path to uevent_helper,nothing happened.
I mean,the device should run "/data/local/tmp/" ,but it didn't.

I've tried toggle bluetooth,wifi etc. still nothing happened.
I'm sure I didn't miss the "chmod 777 /data/local/tmp/" part.

did I miss something or the uevent_helper trick just dosen't work in Android 4.4.2 ?