Re: [PATCH 07/11] iio:health:afe4403 Fix timestamp alignment and prevent data leak.

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 21 May 2020 15:05:37 -0400
"Andrew F. Davis" <afd@ti.com> wrote:

> On 5/21/20 2:45 PM, Jonathan Cameron wrote:
> > On Thu, 21 May 2020 15:44:43 +0100
> > Jonathan Cameron <jic23@jic23.retrosnub.co.uk> wrote:
> >   
> >> On 21 May 2020 14:11:10 BST, "Andrew F. Davis" <afd@ti.com> wrote:  
> >>>
> >>>
> >>> On 5/18/20 12:06 PM, Jonathan Cameron wrote:    
> >>>>
> >>>>
> >>>> On 18 May 2020 01:09:47 BST, "Andrew F. Davis" <afd@ti.com> wrote:    
> >>>>> On 5/17/20 1:29 PM, jic23@kernel.org wrote:    
> >>>>>> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >>>>>>
> >>>>>> One of a class of bugs pointed out by Lars in a recent review.
> >>>>>> iio_push_to_buffers_with_timestamp assumes the buffer used is    
> >>> aligned    
> >>>>>> to the size of the timestamp (8 bytes).  This is not guaranteed in
> >>>>>> this driver which uses a 32 byte array of smaller elements on the    
> >>>>> stack.    
> >>>>>> As Lars also noted this anti pattern can involve a leak of data to
> >>>>>> userspace and that indeed can happen here.  We close both issues by
> >>>>>> moving to a suitable structure in the iio_priv() data with    
> >>> alignment    
> >>>>>> explicitly requested.  This data is allocated with kzalloc so no
> >>>>>> data can leak appart from previous readings.
> >>>>>>
> >>>>>> Fixes: eec96d1e2d31 ("iio: health: Add driver for the TI AFE4403    
> >>>>> heart monitor")    
> >>>>>> Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> >>>>>> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >>>>>> Cc: Andrew F. Davis <afd@ti.com>
> >>>>>> ---
> >>>>>>  drivers/iio/health/afe4403.c | 9 ++++++---
> >>>>>>  1 file changed, 6 insertions(+), 3 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/iio/health/afe4403.c    
> >>>>> b/drivers/iio/health/afe4403.c    
> >>>>>> index e9f87e42ff4f..a3507624b30f 100644
> >>>>>> --- a/drivers/iio/health/afe4403.c
> >>>>>> +++ b/drivers/iio/health/afe4403.c
> >>>>>> @@ -65,6 +65,7 @@ static const struct reg_field    
> >>> afe4403_reg_fields[]    
> >>>>> = {    
> >>>>>>   * @regulator: Pointer to the regulator for the IC
> >>>>>>   * @trig: IIO trigger for this device
> >>>>>>   * @irq: ADC_RDY line interrupt number
> >>>>>> + * @buffer: Used to construct data layout to push into IIO buffer.
> >>>>>>   */
> >>>>>>  struct afe4403_data {
> >>>>>>  	struct device *dev;
> >>>>>> @@ -74,6 +75,8 @@ struct afe4403_data {
> >>>>>>  	struct regulator *regulator;
> >>>>>>  	struct iio_trigger *trig;
> >>>>>>  	int irq;
> >>>>>> +	/* Ensure suitable alignment for timestamp */
> >>>>>> +	s32 buffer[8] __aligned(8);    
> >>>>>
> >>>>>
> >>>>> One of those fancy structs with the timestamp specified would be    
> >>> nice    
> >>>>> here like the other patches. IIRC we have 6 s32 channels, plus a s64
> >>>>> ts.    
> >>>>
> >>>> I think we may only have some of those channels enabled.  So ts may    
> >>> be it several    
> >>>> locations in the buffer. 
> >>>>     
> >>>
> >>> Might have been better to have the ts at the beginning, could have also
> >>> helped with alignment for when an odd number of channels are enabled.    
> >>
> >> Perhaps but for many use cases we don't turn timestamps on and we would need to pad
> >>  anyway for alignment of the fifo. 
> >>  
> >>>    
> >>>> Hence we could use the structure approach but it might give a false    
> >>> sense    
> >>>> of what is going on. 
> >>>>     
> >>>
> >>> That's true, it can always be cleaned later then.    
> >>
> >> Agreed. This is definitely something we can revisit sometime in the future.   
> > 
> > Formal Ack on applying the two afe patches?
> >   
> 
> Acked-by: Andrew F. Davis <afd@ti.com>
Thanks.

Applied to the fixes-togreg branch of iio.git and marked for stable.
These won't go anywhere now until after the merge window.

Thanks,

Jonathan

> 
> > Thanks,
> > 
> > Jonathan  
> >>
> >> J  
> >>>
> >>> Andrew
> >>>    
> >>>> J    
> >>>>>
> >>>>> Other than that everything looks good.
> >>>>>
> >>>>> Andrew
> >>>>>
> >>>>>    
> >>>>>>  };
> >>>>>>  
> >>>>>>  enum afe4403_chan_id {
> >>>>>> @@ -309,7 +312,6 @@ static irqreturn_t afe4403_trigger_handler(int    
> >>>>> irq, void *private)    
> >>>>>>  	struct iio_dev *indio_dev = pf->indio_dev;
> >>>>>>  	struct afe4403_data *afe = iio_priv(indio_dev);
> >>>>>>  	int ret, bit, i = 0;
> >>>>>> -	s32 buffer[8];
> >>>>>>  	u8 tx[4] = {AFE440X_CONTROL0, 0x0, 0x0, AFE440X_CONTROL0_READ};
> >>>>>>  	u8 rx[3];
> >>>>>>  
> >>>>>> @@ -326,7 +328,7 @@ static irqreturn_t afe4403_trigger_handler(int    
> >>>>> irq, void *private)    
> >>>>>>  		if (ret)
> >>>>>>  			goto err;
> >>>>>>  
> >>>>>> -		buffer[i++] = get_unaligned_be24(&rx[0]);
> >>>>>> +		afe->buffer[i++] = get_unaligned_be24(&rx[0]);
> >>>>>>  	}
> >>>>>>  
> >>>>>>  	/* Disable reading from the device */
> >>>>>> @@ -335,7 +337,8 @@ static irqreturn_t afe4403_trigger_handler(int    
> >>>>> irq, void *private)    
> >>>>>>  	if (ret)
> >>>>>>  		goto err;
> >>>>>>  
> >>>>>> -	iio_push_to_buffers_with_timestamp(indio_dev, buffer,    
> >>>>> pf->timestamp);    
> >>>>>> +	iio_push_to_buffers_with_timestamp(indio_dev, afe->buffer,
> >>>>>> +					   pf->timestamp);
> >>>>>>  err:
> >>>>>>  	iio_trigger_notify_done(indio_dev->trig);
> >>>>>>  
> >>>>>>    
> >>>>     
> >>  
> >