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

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Message-ID: <20180715074225.GB15123@gmail.com>
Date:   Sun, 15 Jul 2018 09:42:25 +0200
From:   Marcus Folkesson <marcus.folkesson@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Alexey Khoroshilov <khoroshilov@...ras.ru>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] Input: pxrc - fix leak of usb_device

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.

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 :-)

> 
> Thanks.
> 
> -- 
> Dmitry

Best regards
Marcus Folkesson