linux-kernel - Re: [PATCH v2 17/23] counter: intel-qep: Convert to new counter registration

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Date:   Tue, 28 Dec 2021 11:56:21 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     William Breathitt Gray <vilhelm.gray@...il.com>,
        "Felipe Balbi (Intel)" <balbi@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Raymond Tan <raymond.tan@...el.com>, linux-iio@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v2 17/23] counter: intel-qep: Convert to new counter
 registration

On Mon, Dec 27, 2021 at 05:02:39PM +0200, Jarkko Nikula wrote:
> On 12/27/21 11:45, Uwe Kleine-König wrote:
> > This fixes device lifetime issues where it was possible to free a live
> > struct device.
> > 
> > Fixes: b711f687a1c1 ("counter: Add support for Intel Quadrature Encoder Peripheral")
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > ---
> >   drivers/counter/intel-qep.c | 28 ++++++++++++++++------------
> >   1 file changed, 16 insertions(+), 12 deletions(-)
> > 
> Should the Fixes tag rather be b6c50affda59 ("counter: Add character device
> interface") instead of when each drivers were introduced? I mean was it
> possible to hit the issue before /dev/counter was introduced?

I'm not sure if there is an issue before this, but it was already wrong
before for sure. Maybe it's possible to hold a reference somehow via
sysfs?

The thought that made me tag the individual driver commits was: With the
approach used to fix the issue all drivers need to be modified and an
unconverted driver doesn't benefit from the availability of
counter_alloc() / counter_add() if it isn't used. So all trees that
include b711f687a1c1 but not "counter: intel-qep: Convert to new counter
registration" are broken (more or less exploitable). So I think the
added Fixes line is the right choice.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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