[PATCH v3 25/27] iio:adc:ti-adc12138 Fix alignment issue with timestamp

From: Jonathan Cameron <jic23@kernel.org>
To: linux-iio@vger.kernel.org
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald <pmeerw@pmeerw.net>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Akinobu Mita <akinobu.mita@gmail.com>
Subject: [PATCH v3 25/27] iio:adc:ti-adc12138 Fix alignment issue with timestamp
Date: Wed, 22 Jul 2020 16:51:01 +0100	[thread overview]
Message-ID: <20200722155103.979802-26-jic23@kernel.org> (raw)
In-Reply-To: <20200722155103.979802-1-jic23@kernel.org>

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 an array of smaller elements on the stack.

We move 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. Note that previously
no leak at all could occur, but previous readings should never
be a problem.

In this case the timestamp location depends on what other channels
are enabled. As such we can't use a structure without misleading
by suggesting only one possible timestamp location.

Fixes: 50a6edb1b6e0 ("iio: adc: add ADC12130/ADC12132/ADC12138 ADC driver")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/adc/ti-adc12138.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/ti-adc12138.c b/drivers/iio/adc/ti-adc12138.c
index e485719cd2c4..16f4fd7a04d9 100644
--- a/drivers/iio/adc/ti-adc12138.c
+++ b/drivers/iio/adc/ti-adc12138.c
@@ -47,6 +47,8 @@ struct adc12138 {
 	struct completion complete;
 	/* The number of cclk periods for the S/H's acquisition time */
 	unsigned int acquisition_time;
+	 /* 16x 2 bytes ADC data + 8 bytes timestamp */
+	__be16 data[20] __aligned(8);
 
 	u8 tx_buf[2] ____cacheline_aligned;
 	u8 rx_buf[2];
@@ -329,7 +331,6 @@ static irqreturn_t adc12138_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct adc12138 *adc = iio_priv(indio_dev);
-	__be16 data[20] = { }; /* 16x 2 bytes ADC data + 8 bytes timestamp */
 	__be16 trash;
 	int ret;
 	int scan_index;
@@ -345,7 +346,7 @@ static irqreturn_t adc12138_trigger_handler(int irq, void *p)
 		reinit_completion(&adc->complete);
 
 		ret = adc12138_start_and_read_conv(adc, scan_chan,
-						   i ? &data[i - 1] : &trash);
+					i ? &adc->data[i - 1] : &trash);
 		if (ret) {
 			dev_warn(&adc->spi->dev,
 				 "failed to start conversion\n");
@@ -362,7 +363,7 @@ static irqreturn_t adc12138_trigger_handler(int irq, void *p)
 	}
 
 	if (i) {
-		ret = adc12138_read_conv_data(adc, &data[i - 1]);
+		ret = adc12138_read_conv_data(adc, &adc->data[i - 1]);
 		if (ret) {
 			dev_warn(&adc->spi->dev,
 				 "failed to get conversion data\n");
@@ -370,7 +371,7 @@ static irqreturn_t adc12138_trigger_handler(int irq, void *p)
 		}
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, data,
+	iio_push_to_buffers_with_timestamp(indio_dev, adc->data,
 					   iio_get_time_ns(indio_dev));
 out:
 	mutex_unlock(&adc->lock);
-- 
2.27.0

