[v3,14/27] iio:magnetometer:mag3110 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.
This data is allocated with kzalloc so no data can leak apart from
previous readings.

The explicit alignment of ts is not necessary in this case but
does make the code slightly less fragile so I have included it.

Fixes: 39631b5f9584 ("iio: Add Freescale mag3110 magnetometer driver")
Reported-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>
---
 drivers/iio/magnetometer/mag3110.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

Comments

Andy Shevchenko July 23, 2020, 12:13 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.
> This data is allocated with kzalloc so no data can leak apart from
> previous readings.
>
> The explicit alignment of ts is not necessary in this case but
> does make the code slightly less fragile so I have included it.
>

I broke my eyes and brain over temp.
At first I thought it was temporary garbage like in the other patch,
but now I'm guessing (looking into the comment) that this is
temperature.
Can we spell it fully?

...

> +               u8 temp;

> -       u8 buffer[16]; /* 3 16-bit channels + 1 byte temp + padding + ts */

> +               data->scan.temp = ret;

Patch

diff --git a/drivers/iio/magnetometer/mag3110.c b/drivers/iio/magnetometer/mag3110.c
index 4d305a21c379..e96113ca39bd 100644
--- a/drivers/iio/magnetometer/mag3110.c
+++ b/drivers/iio/magnetometer/mag3110.c
@@ -56,6 +56,12 @@  struct mag3110_data {
 	int sleep_val;
 	struct regulator *vdd_reg;
 	struct regulator *vddio_reg;
+	/* Ensure natural alignment of timestamp */
+	struct {
+		__be16 channels[3];
+		u8 temp;
+		s64 ts __aligned(8);
+	} scan;
 };
 
 static int mag3110_request(struct mag3110_data *data)
@@ -387,10 +393,9 @@  static irqreturn_t mag3110_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct mag3110_data *data = iio_priv(indio_dev);
-	u8 buffer[16]; /* 3 16-bit channels + 1 byte temp + padding + ts */
 	int ret;
 
-	ret = mag3110_read(data, (__be16 *) buffer);
+	ret = mag3110_read(data, data->scan.channels);
 	if (ret < 0)
 		goto done;
 
@@ -399,10 +404,10 @@  static irqreturn_t mag3110_trigger_handler(int irq, void *p)
 			MAG3110_DIE_TEMP);
 		if (ret < 0)
 			goto done;
-		buffer[6] = ret;
+		data->scan.temp = ret;
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
+	iio_push_to_buffers_with_timestamp(indio_dev, &data->scan,
 		iio_get_time_ns(indio_dev));
 
 done: