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

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Date:   Thu, 5 Apr 2018 00:31:11 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [GIT PULL] USB/PHY driver patches for 4.17-rc1

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@...uxfoundation.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.