linux-kernel - Re: [PATCH v2] iio: light: veml6030: add support for triggered buffer

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Message-ID: <101820df-d6c6-4032-8e1e-d3d8b85720c4@gmail.com>
Date: Sun, 24 Nov 2024 15:47:23 +0100
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: light: veml6030: add support for triggered buffer

On 24/11/2024 13:43, Jonathan Cameron wrote:
>>>> +static irqreturn_t veml6030_trigger_handler(int irq, void *p)
>>>> +{
>>>> +	struct iio_poll_func *pf = p;
>>>> +	struct iio_dev *iio = pf->indio_dev;
>>>> +	struct veml6030_data *data = iio_priv(iio);
>>>> +	unsigned int reg;
>>>> +	int ch, ret, i = 0;
>>>> +	struct {
>>>> +		u16 chans[2];  
>>> There is a hole here...   
>>>> +		aligned_s64 timestamp;
>>>> +	} scan;
>>>> +
>>>> +	iio_for_each_active_channel(iio, ch) {
>>>> +		ret = regmap_read(data->regmap, VEML6030_REG_DATA(ch),
>>>> +				  &reg);
>>>> +		if (ret)
>>>> +			goto done;
>>>> +
>>>> +		scan.chans[i++] = reg;  
>>> This fills in at least 1 channel, but maybe not the second.  
>>>> +	}
>>>> +  
>>> So this leaks random stack data I think.
>>>
>>> Upshot, when holes are involved or not all the channels are set, need
>>> memset(&scan, 0, sizeof(scan));
>>> for the structure on the stack which will zero the holes as well as
>>> both channels.
>>>
>>> Ancient article on this: https://lwn.net/Articles/417989/
>>>
>>> We get away with it when they are in the iio_priv space because they are
>>> kzalloc + if we do leak data due to changes in configured channels it's
>>> just old sensor data which is (I think) never a security problem!
>>>   
>>>> +	iio_push_to_buffers_with_timestamp(iio, &scan, pf->timestamp);
>>>> +
>>>> +done:
>>>> +	iio_trigger_notify_done(iio->trig);
>>>> +
>>>> +	return IRQ_HANDLED;
>>>> +}
>>>> +
>>>>  static int veml6030_set_info(struct iio_dev *indio_dev)
>>>>  {
>>>>  	struct veml6030_data *data = iio_priv(indio_dev);
>>>> @@ -1077,6 +1145,12 @@ static int veml6030_probe(struct i2c_client *client)
>>>>  	if (ret < 0)
>>>>  		return ret;
>>>>  
>>>> +	ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev, NULL,
>>>> +					      veml6030_trigger_handler, NULL);
>>>> +	if (ret)
>>>> +		return dev_err_probe(&client->dev, ret,
>>>> +				     "Failed to register triggered buffer");
>>>> +
>>>>  	return devm_iio_device_register(&client->dev, indio_dev);
>>>>  }
>>>>  
>>>>
>>>> ---
>>>> base-commit: 9dd2270ca0b38ee16094817f4a53e7ba78e31567
>>>> change-id: 20241106-veml6030_triggered_buffer-a38886ca4cce
>>>>
>>>> Best regards,  
>>>   
>>
>>
>> Hi Jonathan,
>>
>> thanks a lot for your explanation and the link, it makes perfect sense.
>> By the way, when I moved this struct from the iio_priv to the function,
>> I took a look at some existing code, and a couple of them might have the
>> same issue:
>>
>> - temperature/tmp006.c: it also has a hole between the two 16-bit
>> channels and the timestamp (aligned(8)), but it is not set to zero.
>>
>> - adc/ti-ads1119.c: the scan consists of an unsigned int and the
>> timestamp (aligned(8)). I believe there is a hole there as well.
>>
>> I did not go over all drivers (most of them store the scan struct in the
>> iio_priv space anyway), but at least those two look suspicious.
>>
>> Should I fix (e.g. memset) those two I mentioned?
> 
> Please do.  Thanks!
> 
> Jonathan
> 

Ok, I will take a closer look to check if there are more drivers leaking
uninitialized data. By the way, would you tag the fixes for stable? This
becoming an attack vector might be a bit theoretical, and I don't know
the consensus about the danger of passing uninitialized data to userspace.

Thanks again,
Javier Carrasco