[PATCH 3/4] drivers/misc: Add ASpeed LPC control driver

[Greg KH]

On Thu, Jan 12, 2017 at 09:27:47AM -0600, Benjamin Herrenschmidt wrote:
> On Thu, 2017-01-12 at 11:30 +0100, Greg KH wrote:
> > > > And don't call access_ok(), it's racy and no driver should ever do that.
> > > > 
> > > 
> > > Oh, duly noted. I'll be sure to check out how and why. Perhaps it
> > > would be wise that no driver actually do that, I'm quite sure I used
> > > other drivers as examples of best practice.
> > 
> > You did?  Please point me at that code so we can fix them up properly.
> > Cargo-cult coding is not a good thing, but it happens, so if we can at
> > least provide clean code to fixate on, it's good overall for everyone.
> 
> How so ? I mean, access_ok followed by __get/__put_user is still a
> classic, what's wrong with it ?

No "normal" driver should do that, just call copy_to/from_user and be
done with it.  That way all of the proper locking and validation checks
like this are done correctly for you.  Why would a driver ever call the
"raw" __get/__put_user functions?

thanks,

greg k-h