[v3,23/27] iio:adc:ti-ads124s08 Fix alignment and data leak issues.

Commit Message

Jonathan Cameron July 22, 2020, 3:50 p.m. UTC

From: Jonathan Cameron <[e-mail]>

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 an 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 apart from previous readings.

In this driver the timestamp can end up in various different locations
depending on what other channels are enabled.  As a result, we don't
use a structure to specify it's position as that would be missleading.

Fixes: e717f8c6dfec ("iio: adc: Add the TI ads124s08 ADC code")
Reported-by: Lars-Peter Clausen <[e-mail]>
Cc: Dan Murphy <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>
---
 drivers/iio/adc/ti-ads124s08.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Comments

Andy Shevchenko July 22, 2020, 8:54 p.m. UTC | #1

On Wed, Jul 22, 2020 at 6:53 PM Jonathan Cameron <[e-mail]> wrote:
>
> From: Jonathan Cameron <[e-mail]>
>
> 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 an 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 apart from previous readings.
>
> In this driver the timestamp can end up in various different locations
> depending on what other channels are enabled.  As a result, we don't
> use a structure to specify it's position as that would be missleading.

...

> +       /*
> +        * Used to correctly align data.
> +        * Ensure timestamp is naturally aligned.
> +        */
> +       u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8);

u32 vs. u16?

Jonathan Cameron July 23, 2020, 11:23 a.m. UTC | #2

On Wed, 22 Jul 2020 23:54:29 +0300
Andy Shevchenko <[e-mail]> wrote:

> On Wed, Jul 22, 2020 at 6:53 PM Jonathan Cameron <[e-mail]> wrote:
> >
> > From: Jonathan Cameron <[e-mail]>
> >
> > 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 an 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 apart from previous readings.
> >
> > In this driver the timestamp can end up in various different locations
> > depending on what other channels are enabled.  As a result, we don't
> > use a structure to specify it's position as that would be missleading.  
> 
> ...
> 
> > +       /*
> > +        * Used to correctly align data.
> > +        * Ensure timestamp is naturally aligned.
> > +        */
> > +       u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8);  
> 
> u32 vs. u16?
> 
Curious indeed.  My eyes jumped straight over that when cutting and
pasting that line.  I guess too big is never a problem, but should definitely
tidy that up.

Thanks,

Jonathan

Patch

diff --git a/drivers/iio/adc/ti-ads124s08.c b/drivers/iio/adc/ti-ads124s08.c
index 4b4fbe33930c..734ee5d82ff6 100644
--- a/drivers/iio/adc/ti-ads124s08.c
+++ b/drivers/iio/adc/ti-ads124s08.c
@@ -99,6 +99,11 @@  struct ads124s_private {
 	struct gpio_desc *reset_gpio;
 	struct spi_device *spi;
 	struct mutex lock;
+	/*
+	 * Used to correctly align data.
+	 * Ensure timestamp is naturally aligned.
+	 */
+	u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8);
 	u8 data[5] ____cacheline_aligned;
 };
 
@@ -269,7 +274,6 @@  static irqreturn_t ads124s_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct ads124s_private *priv = iio_priv(indio_dev);
-	u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)];
 	int scan_index, j = 0;
 	int ret;
 
@@ -284,7 +288,7 @@  static irqreturn_t ads124s_trigger_handler(int irq, void *p)
 		if (ret)
 			dev_err(&priv->spi->dev, "Start ADC conversions failed\n");
 
-		buffer[j] = ads124s_read(indio_dev, scan_index);
+		priv->buffer[j] = ads124s_read(indio_dev, scan_index);
 		ret = ads124s_write_cmd(indio_dev, ADS124S08_STOP_CONV);
 		if (ret)
 			dev_err(&priv->spi->dev, "Stop ADC conversions failed\n");
@@ -292,7 +296,7 @@  static irqreturn_t ads124s_trigger_handler(int irq, void *p)
 		j++;
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
+	iio_push_to_buffers_with_timestamp(indio_dev, priv->buffer,
 			pf->timestamp);
 
 	iio_trigger_notify_done(indio_dev->trig);