linux-kernel - Re: [PATCH] USB: serial: fix invalid user-pointer checks

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Date:   Wed, 9 Nov 2016 12:07:09 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Johan Hovold <johan@...nel.org>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] USB: serial: fix invalid user-pointer checks

On Wed, Nov 09, 2016 at 11:58:31AM +0100, Oliver Neukum wrote:
> On Tue, 2016-11-08 at 16:41 +0100, Johan Hovold wrote:
> > On Tue, Nov 08, 2016 at 03:13:13PM +0100, Oliver Neukum wrote:
> > > On Tue, 2016-11-08 at 13:26 +0100, Johan Hovold wrote:
> > > > Drop invalid user-pointer checks from ioctl handlers.
> > > > 
> > > > A NULL-pointer can be valid in user space and copy_to_user() takes
> > > > care
> > > > of sanity checking.
> > > 
> > > Shouldn't we bail out early in these cases?
> > 
> > I don't think it's worth it, and this is also the general pattern for
> > such ioctls. The added overhead for an error case like this is really
> > negligible.
> 
> OK, as you say.

Also remember that access_ok() is not a sufficient sanity check, and
would specifically fail to catch the NULL-pointer case.

Thanks,
Johan