patch "iio:adc:ti-ads124s08: Fix alignment and data leak issues." added to staging-testing

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    iio:adc:ti-ads124s08: Fix alignment and data leak issues.

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the staging-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


From 1e405bc2512f80a903ddd6ba8740cee885238d7f Mon Sep 17 00:00:00 2001
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Date: Sun, 20 Sep 2020 12:27:42 +0100
Subject: iio:adc:ti-ads124s08: Fix alignment and data leak issues.

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 misleading.

Fixes: e717f8c6dfec ("iio: adc: Add the TI ads124s08 ADC code")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Dan Murphy <dmurphy@ti.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200920112742.170751-9-jic23@kernel.org
---
 drivers/iio/adc/ti-ads124s08.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ti-ads124s08.c b/drivers/iio/adc/ti-ads124s08.c
index eff4f9a9898e..b4a128b19188 100644
--- a/drivers/iio/adc/ti-ads124s08.c
+++ b/drivers/iio/adc/ti-ads124s08.c
@@ -99,6 +99,14 @@ 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.
+	 * Note that the full buffer length may not be needed if not
+	 * all channels are enabled, as long as the alignment of the
+	 * timestamp is maintained.
+	 */
+	u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u32)] __aligned(8);
 	u8 data[5] ____cacheline_aligned;
 };
 
@@ -269,7 +277,6 @@ 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(u32)];
 	int scan_index, j = 0;
 	int ret;
 
@@ -284,7 +291,7 @@ 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 +299,7 @@ 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);
-- 
2.29.2