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

["Andrew F. Davis" <afd@ti.com>]

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,
> 
> 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);
>>>>>>  
>>>>>>  
>>>>   
>>
>