[PATCH v3 5/5] iio: as73211: copy/release available integration times to fix race

[Matteo Martelli <matteomartelli3@gmail.com>]

While available integration times are being printed to sysfs by iio core
(iio_read_channel_info_avail), the sampling frequency might be changed.
This could cause the buffer shared with iio core to be corrupted. To
prevent it, make a copy of the integration times buffer and free it in
the read_avail_release_resource callback.

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
---
 drivers/iio/light/as73211.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/light/as73211.c b/drivers/iio/light/as73211.c
index be0068081ebbbb37fdfb252b67a77b302ff725f6..c4c94873e6a1cc926cfb724d906b07222773c43f 100644
--- a/drivers/iio/light/as73211.c
+++ b/drivers/iio/light/as73211.c
@@ -108,7 +108,8 @@ struct as73211_spec_dev_data {
  * @creg1:  Cached Configuration Register 1.
  * @creg2:  Cached Configuration Register 2.
  * @creg3:  Cached Configuration Register 3.
- * @mutex:  Keeps cached registers in sync with the device.
+ * @mutex:  Keeps cached registers in sync with the device and protects
+ *          int_time_avail concurrent access for updating and reading.
  * @completion: Completion to wait for interrupt.
  * @int_time_avail: Available integration times (depend on sampling frequency).
  * @spec_dev: device-specific configuration.
@@ -493,17 +494,32 @@ static int as73211_read_avail(struct iio_dev *indio_dev, struct iio_chan_spec co
 		*type = IIO_VAL_INT;
 		return IIO_AVAIL_LIST;
 
-	case IIO_CHAN_INFO_INT_TIME:
+	case IIO_CHAN_INFO_INT_TIME: {
 		*length = ARRAY_SIZE(data->int_time_avail);
-		*vals = data->int_time_avail;
 		*type = IIO_VAL_INT_PLUS_MICRO;
-		return IIO_AVAIL_LIST;
 
+		guard(mutex)(&data->mutex);
+
+		*vals = kmemdup_array(data->int_time_avail, *length,
+				      sizeof(int), GFP_KERNEL);
+		if (!*vals)
+			return -ENOMEM;
+
+		return IIO_AVAIL_LIST;
+	}
 	default:
 		return -EINVAL;
 	}
 }
 
+static void as73211_read_avail_release_res(struct iio_dev *indio_dev,
+					   struct iio_chan_spec const *chan,
+					   const int *vals, long mask)
+{
+	if (mask == IIO_CHAN_INFO_INT_TIME)
+		kfree(vals);
+}
+
 static int _as73211_write_raw(struct iio_dev *indio_dev,
 			       struct iio_chan_spec const *chan __always_unused,
 			       int val, int val2, long mask)
@@ -699,6 +715,7 @@ static irqreturn_t as73211_trigger_handler(int irq __always_unused, void *p)
 static const struct iio_info as73211_info = {
 	.read_raw = as73211_read_raw,
 	.read_avail = as73211_read_avail,
+	.read_avail_release_resource = as73211_read_avail_release_res,
 	.write_raw = as73211_write_raw,
 };
 

-- 
2.47.0