[v3,11/27] iio:light:st_uvis25 Fix timestamp alignment and prevent data leak.

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()

This data is allocated with kzalloc so no data can leak apart
from previous readings.

A local unsigned int variable is used for the regmap call so it
is clear there is no potential issue with writing into the padding
of the structure.

Fixes: 3025c8688c1e ("iio: light: add support for UVIS25 sensor")
Reported-by: Lars-Peter Clausen <[e-mail]>
Acked-by: Lorenzo Bianconi <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>
---
 drivers/iio/light/st_uvis25.h      | 5 +++++
 drivers/iio/light/st_uvis25_core.c | 8 +++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

Comments

Andy Shevchenko July 22, 2020, 7:48 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()
>
> This data is allocated with kzalloc so no data can leak apart
> from previous readings.
>
> A local unsigned int variable is used for the regmap call so it
> is clear there is no potential issue with writing into the padding
> of the structure.

...

> +               u8 chan;

> +       hw->scan.chan = val & 0xFF;

0xFF is not needed.

Patch

diff --git a/drivers/iio/light/st_uvis25.h b/drivers/iio/light/st_uvis25.h
index 78bc56aad129..283086887caf 100644
--- a/drivers/iio/light/st_uvis25.h
+++ b/drivers/iio/light/st_uvis25.h
@@ -27,6 +27,11 @@  struct st_uvis25_hw {
 	struct iio_trigger *trig;
 	bool enabled;
 	int irq;
+	/* Ensure timestamp is naturally aligned */
+	struct {
+		u8 chan;
+		s64 ts __aligned(8);
+	} scan;
 };
 
 extern const struct dev_pm_ops st_uvis25_pm_ops;
diff --git a/drivers/iio/light/st_uvis25_core.c b/drivers/iio/light/st_uvis25_core.c
index a18a82e6bbf5..50d9850256fc 100644
--- a/drivers/iio/light/st_uvis25_core.c
+++ b/drivers/iio/light/st_uvis25_core.c
@@ -232,17 +232,19 @@  static const struct iio_buffer_setup_ops st_uvis25_buffer_ops = {
 
 static irqreturn_t st_uvis25_buffer_handler_thread(int irq, void *p)
 {
-	u8 buffer[ALIGN(sizeof(u8), sizeof(s64)) + sizeof(s64)];
 	struct iio_poll_func *pf = p;
 	struct iio_dev *iio_dev = pf->indio_dev;
 	struct st_uvis25_hw *hw = iio_priv(iio_dev);
+	unsigned int val;
 	int err;
 
-	err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR, (int *)buffer);
+	err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR, &val);
 	if (err < 0)
 		goto out;
 
-	iio_push_to_buffers_with_timestamp(iio_dev, buffer,
+	hw->scan.chan = val & 0xFF;
+
+	iio_push_to_buffers_with_timestamp(iio_dev, &hw->scan,
 					   iio_get_time_ns(iio_dev));
 
 out: