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

Greg KH gregkh at linuxfoundation.org
Fri Jan 13 03:26:19 AEDT 2017

On Thu, Jan 12, 2017 at 10:07:33AM -0600, Benjamin Herrenschmidt wrote:
> On Thu, 2017-01-12 at 17:00 +0100, Greg KH wrote:
> > > 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?
> I supposed historically it was considered faster for some things :-)
> Not a huge deal, and yes it's probably cleaner, I was just wondering
> what was "racy" about access_ok() that I might have missed...

I think, you can change things after access_ok() happens, there used to
be bugs in that area a few years ago.  I think we fixed them by moving
the offending drivers to use copy_*() instead.


greg k-h

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