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

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 21 May 2020 15:44:43 +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?

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);
> >>>>  
> >>>>  
> >>   
>