linux-kernel - RE: [PATCH 2/2] iio: inkern: add error case in iio_channel

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Date:	Fri, 14 Sep 2012 00:59:01 +0000
From:	"Kim, Milo" <Milo.Kim@...com>
To:	Jonathan Cameron <jic23@...23.retrosnub.co.uk>
CC:	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] iio: inkern: add error case in iio_channel_get()

> On 10/09/12 09:02, Kim, Milo wrote:
> >   The datasheet name is defined in the IIO driver.
> >   On the other hand, the adc_channel_label is configured in
> >   the platform machine side.
> >   If the datasheet name is not matched with any adc_channel_label,
> >   the iio_channel_get() should be returned as error for preventing
> >   using invalid IIO channel data.
> >
> >   Moreover, this patch detects NULL pointer dereference problem at
> early time.
> >   In general, the IIO driver just accesses to any member of the
> iio_chan_spec
> >   in own xxx_read_raw() function.
> >   If the iio_chan_spec is invalid pointer, NULL dereference problem
> may occur
> >   such like 'iio_chan_spec->channel' or 'iio_chan_spec->type'.
> >   If the iio_channel_get() gets failed in the IIO consumer,
> >   then no read_raw() operation proceeds.

> I guess this is marginally cleaner, but either way it is up to the
> calling driver to check whether the call succeeded.

IMO, it would be better if iio_channel_get() gets failed
when the consumer tries to get the channel rather than when using it.

The channel spec is retrieved when the channel is requested, - iio_channel_get()
So it's reasonable if error returns in case of invalid channel spcec.

And I just found similar handling in iio_channel_get_all().
But my patch needs releasing the memory as Lars-Peter noted.

Thanks !

Best Regards,
Milo 

> >
> > Signed-off-by: Milo(Woogyom) Kim <milo.kim@...com>
> > ---
> >   drivers/iio/inkern.c |    6 +++++-
> >   1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> > index 1faa240..a5caf6b 100644
> > --- a/drivers/iio/inkern.c
> > +++ b/drivers/iio/inkern.c
> > @@ -136,11 +136,15 @@ struct iio_channel *iio_channel_get(const char
> *name, const char *channel_name)
> >
> >   	channel->indio_dev = c->indio_dev;
> >
> > -	if (c->map->adc_channel_label)
> > +	if (c->map->adc_channel_label) {
> >   		channel->channel =
> >   			iio_chan_spec_from_name(channel->indio_dev,
> >   						c->map->adc_channel_label);
> >
> > +		if (channel->channel == NULL)
> > +			return ERR_PTR(-ENODEV);
> > +	}
> > +
> >   	return channel;
> >   }
> >   EXPORT_SYMBOL_GPL(iio_channel_get);
> >

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