Re: [GIT PULL] USB/PHY driver patches for 4.17-rc1

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Apr 05, 2018 at 12:31:11AM -0700, Christoph Hellwig wrote:
> On Thu, Apr 05, 2018 at 09:19:28AM +0200, Lars-Peter Clausen wrote:
> > On 04/05/2018 08:31 AM, Kees Cook wrote:
> > > On Wed, Apr 4, 2018 at 3:31 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > >> Lars-Peter Clausen (2):
> > >>       usb: gadget: ffs: Execute copy_to_user() with USER_DS set
> > > 
> > > https://git.kernel.org/linus/4058ebf33cb0be88ca516f968eda24ab7b6b93e4
> > > 
> > > Isn't there a better way to do this without the set_fs() usage? We've
> > > been try to eliminate it in the kernel. I thought there was a safer
> > > way to use iters now?
> > 
> > The problem is use_mm(). It needs to be accompanied with set_fs(DS_USER) to
> > work reliably. This has simply been missing for this particular instance of
> > use_mm().
> 
> To me it seems like use_mm() should do set_fs(USER_DS) and unuse_mm()
> should do set_fs(KERNEL_DS) to get drivers outo of this mess.  I'll see
> if I can come up with patches for the next merge window.

Yes on the former, not quite on the latter (we need to go back to the state
before use_mm()).  Said that, drm users of use_mm() look rather fishy and
might be worth a good look...