[PATCH v1] proc/vmcore: fix clearing user buffer by properly using clear_user()

[David Hildenbrand]

> > "that allows supervisor mode programs to optionally set user-space
> > memory mappings so that access to those mappings from supervisor mode
> > will cause a trap. This makes it harder for malicious programs to
> > "trick" the kernel into using instructions or data from a user-space
> > program"
>
> OK, probably. I thought it's triggered in access_ok(), and tried to
> figure out why. But seems we should do something to check this in
> access_ok(), otherwise the logic of clear_user/_clear_user is not so
> reasonable. Anyway, I have learned it, thanks a lot for digging it out.
>
> By the way, I can't open above wiki article, found below commit from
> hpa. Maybe we can add some into log to tell this, not strong opinin,
> leave it to you.

Yes, now that we know the root cause I'll add some more details to the
patch description and resend -- thanks Baoquan!