linux-kernel - Re: [PATCH] Input: pxrc

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Message-ID: <CAKdAkRS0NBOo7thkevZAQXBWt_ReppjdPz6a6PQ6LtJHbPYgVg@mail.gmail.com>
Date:   Sun, 15 Jul 2018 13:06:32 +0300
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Marcus Folkesson <marcus.folkesson@...il.com>
Cc:     Alexey Khoroshilov <khoroshilov@...ras.ru>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        ldv-project@...uxtesting.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] Input: pxrc - fix leak of usb_device

On Sun, Jul 15, 2018 at 10:42 AM Marcus Folkesson
<marcus.folkesson@...il.com> wrote:
>
> On Sat, Jul 14, 2018 at 08:51:09AM +0000, Dmitry Torokhov wrote:
> > On Sat, Jul 14, 2018 at 10:09:20AM +0200, Marcus Folkesson wrote:
> > > Hi Alexey,
> > >
> > > Good catch!
> > >
> > > On Fri, Jul 13, 2018 at 11:07:57PM +0300, Alexey Khoroshilov wrote:
> > > > pxrc_probe() calls usb_get_dev(), but there is no usb_put_dev()
> > > > anywhere in the driver.
> > > >
> > > > The patch adds one to error handling code and to pxrc_disconnect().
> > > >
> > > > Found by Linux Driver Verification project (linuxtesting.org).
> > > >
> > > > Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
> > >
> > > Reviewed-by: Marcus Folkesson <marcus.folkesson@...il.com>
> >
> > Hmm, the biggest question however if we need to "take" the device, as I
> > do not think interface can outlive the device, and whether we actually
> > need to store it in pxrc, as we only need it during set up, as far as I
> > can see.
>
> Yep, the device is only used during setup.
> I interpret the comments for usb_get_dev() as you should take a
> reference count on the device even if you only use the interface, but I
> could be wrong.
>
> From usb_get_dev()::
>
>          * usb_get_dev - increments the reference count of the usb device structure
>          * @dev: the device being referenced
>          *
>          * Each live reference to a device should be refcounted.
>          *
>          * Drivers for USB interfaces should normally record such references in
>          * their probe() methods, when they bind to an interface, and release
>          * them by calling usb_put_dev(), in their disconnect() methods.

Hmm, usb device is a parent of usb interface so our driver model rules
ensure that usb device should not disappear while interface device is
still there. Greg, is this comment still valid?

>
> I can fix the driver to not take the device if that is what we want.
> If not Alexey want to fix it of course, it is his catch :-)

Yeah, I'd prefer doing this if possible.

Thanks.

-- 
Dmitry