patch "iio:light:si1145: Fix timestamp alignment and prevent data leak." added to staging-next

[<gregkh@linuxfoundation.org>]

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

    iio:light:si1145: Fix timestamp alignment and prevent data leak.

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-next 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 also be merged in the next major kernel release
during the merge window.

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


From 0456ecf34d466261970e0ff92b2b9c78a4908637 Mon Sep 17 00:00:00 2001
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Date: Wed, 22 Jul 2020 16:50:44 +0100
Subject: iio:light:si1145: Fix timestamp alignment and prevent data leak.

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 a 24 byte 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 array in the iio_priv() data with alignment
explicitly requested.  This data is allocated with kzalloc so no
data can leak appart from previous readings.

Depending on the enabled channels, the  location of the timestamp
can be at various aligned offsets through the buffer.  As such we
any use of a structure to enforce this alignment would incorrectly
suggest a single location for the timestamp.  Comments adjusted to
express this clearly in the code.

Fixes: ac45e57f1590 ("iio: light: Add driver for Silabs si1132, si1141/2/3 and si1145/6/7 ambient light, uv index and proximity sensors")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200722155103.979802-9-jic23@kernel.org
---
 drivers/iio/light/si1145.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/light/si1145.c b/drivers/iio/light/si1145.c
index 155faaea8c72..087ef953041d 100644
--- a/drivers/iio/light/si1145.c
+++ b/drivers/iio/light/si1145.c
@@ -168,6 +168,7 @@ struct si1145_part_info {
  * @part_info:	Part information
  * @trig:	Pointer to iio trigger
  * @meas_rate:	Value of MEAS_RATE register. Only set in HW in auto mode
+ * @buffer:	Used to pack data read from sensor.
  */
 struct si1145_data {
 	struct i2c_client *client;
@@ -179,6 +180,14 @@ struct si1145_data {
 	bool autonomous;
 	struct iio_trigger *trig;
 	int meas_rate;
+	/*
+	 * Ensure timestamp will be naturally aligned if present.
+	 * Maximum buffer size (may be only partly used if not all
+	 * channels are enabled):
+	 *   6*2 bytes channels data + 4 bytes alignment +
+	 *   8 bytes timestamp
+	 */
+	u8 buffer[24] __aligned(8);
 };
 
 /*
@@ -440,12 +449,6 @@ static irqreturn_t si1145_trigger_handler(int irq, void *private)
 	struct iio_poll_func *pf = private;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct si1145_data *data = iio_priv(indio_dev);
-	/*
-	 * Maximum buffer size:
-	 *   6*2 bytes channels data + 4 bytes alignment +
-	 *   8 bytes timestamp
-	 */
-	u8 buffer[24];
 	int i, j = 0;
 	int ret;
 	u8 irq_status = 0;
@@ -478,7 +481,7 @@ static irqreturn_t si1145_trigger_handler(int irq, void *private)
 
 		ret = i2c_smbus_read_i2c_block_data_or_emulated(
 				data->client, indio_dev->channels[i].address,
-				sizeof(u16) * run, &buffer[j]);
+				sizeof(u16) * run, &data->buffer[j]);
 		if (ret < 0)
 			goto done;
 		j += run * sizeof(u16);
@@ -493,7 +496,7 @@ static irqreturn_t si1145_trigger_handler(int irq, void *private)
 			goto done;
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
+	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
 		iio_get_time_ns(indio_dev));
 
 done:
-- 
2.28.0