patch "iio:adc:max1118 Fix alignment of timestamp and data leak issues" added to staging-linus

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

iio:adc:max1118 Fix alignment of timestamp 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-linus 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 hopefully also be merged in Linus's tree for the next -rc kernel release.

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

From db8f06d97ec284dc018e2e4890d2e5035fde8630 Mon Sep 17 00:00:00 2001
From: Jonathan Cameron <[email protected]>
Date: Wed, 22 Jul 2020 16:51:03 +0100
Subject: iio:adc:max1118 Fix alignment of timestamp 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.

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

The explicit alignment of ts is necessary to ensure correct padding on architectures where s64 is only 4 bytes aligned such as x86_32.

---
 drivers/iio/adc/max1118.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

index 01b20e420ac4..6efb0b43d938 100644
@@ -36,6 +36,11 @@ struct max1118 {
 	struct spi_device *spi;
 	struct mutex lock;
 	struct regulator *reg;
+	/* Ensure natural alignment of buffer elements */
+	struct {
+		u8 channels[2];
+		s64 ts __aligned(8);
+	} scan;
 
 	u8 data ____cacheline_aligned;
 };

@@ -166,7 +171,6 @@ static irqreturn_t max1118_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct max1118 *adc = iio_priv(indio_dev);
-	u8 data[16] = { }; /* 2x 8-bit ADC data + padding + 8 bytes timestamp */
 	int scan_index;
 	int i = 0;
 

@@ -184,10 +188,10 @@ static irqreturn_t max1118_trigger_handler(int irq, void *p)
 			goto out;
 		}
 
-		data[i] = ret;
+		adc->scan.channels[i] = ret;
 		i++;
 	}
-	iio_push_to_buffers_with_timestamp(indio_dev, data,
+	iio_push_to_buffers_with_timestamp(indio_dev, &adc->scan,
 					   iio_get_time_ns(indio_dev));
 out:
 	mutex_unlock(&adc->lock);

2.28.0