linux-kernel - [PATCH] iio: potentiometer: ds1803: remove VLA usage

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Date:   Tue, 13 Mar 2018 10:23:43 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] iio: potentiometer: ds1803: remove VLA usage

In preparation to enabling -Wvla, remove VLA. In this particular
case use macro ARRAY_SIZE so the length of array _result_ can be
computed at preprocessing time.

The use of stack Variable Length Arrays needs to be avoided, as they
can be a vector for stack exhaustion, which can be both a runtime bug
or a security flaw. Also, in general, as code evolves it is easy to
lose track of how big a VLA can get. Thus, we can end up having runtime
failures that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/iio/potentiometer/ds1803.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/potentiometer/ds1803.c b/drivers/iio/potentiometer/ds1803.c
index 9b0ff4a..6bf12c9 100644
--- a/drivers/iio/potentiometer/ds1803.c
+++ b/drivers/iio/potentiometer/ds1803.c
@@ -64,7 +64,7 @@ static int ds1803_read_raw(struct iio_dev *indio_dev,
 	struct ds1803_data *data = iio_priv(indio_dev);
 	int pot = chan->channel;
 	int ret;
-	u8 result[indio_dev->num_channels];
+	u8 result[ARRAY_SIZE(ds1803_channels)];
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-- 
2.7.4