[PATCH v3 4/5] iio: ad7192: copy/release available filter frequencies to fix race

[Matteo Martelli <matteomartelli3@xxxxxxxxx>]

While available filter frequencies 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 filter frequencies buffer
and free it in the read_avail_release_resource callback.

Signed-off-by: Matteo Martelli <matteomartelli3@xxxxxxxxx>
---
 drivers/iio/adc/ad7192.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/ad7192.c b/drivers/iio/adc/ad7192.c
index 7042ddfdfc03ee5ea58ca07fb1943feb6538175b..acf625ced0b21db8d44f77929e8a875b3c10e1b1 100644
--- a/drivers/iio/adc/ad7192.c
+++ b/drivers/iio/adc/ad7192.c
@@ -1056,12 +1056,19 @@ static int ad7192_read_avail(struct iio_dev *indio_dev,
 		*length = ARRAY_SIZE(st->scale_avail) * 2;
 
 		return IIO_AVAIL_LIST;
-	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
-		*vals = (int *)st->filter_freq_avail;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY: {
 		*type = IIO_VAL_FRACTIONAL;
 		*length = ARRAY_SIZE(st->filter_freq_avail) * 2;
 
+		guard(mutex)(&st->lock);
+
+		*vals = kmemdup_array((int *)st->filter_freq_avail, *length,
+				      sizeof(int), GFP_KERNEL);
+		if (!*vals)
+			return -ENOMEM;
+
 		return IIO_AVAIL_LIST;
+	}
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
 		*vals = (int *)st->oversampling_ratio_avail;
 		*type = IIO_VAL_INT;
@@ -1073,6 +1080,14 @@ static int ad7192_read_avail(struct iio_dev *indio_dev,
 	return -EINVAL;
 }
 
+static void ad7192_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_LOW_PASS_FILTER_3DB_FREQUENCY)
+		kfree(vals);
+}
+
 static int ad7192_update_scan_mode(struct iio_dev *indio_dev, const unsigned long *scan_mask)
 {
 	struct ad7192_state *st = iio_priv(indio_dev);
@@ -1098,6 +1113,7 @@ static const struct iio_info ad7192_info = {
 	.write_raw = ad7192_write_raw,
 	.write_raw_get_fmt = ad7192_write_raw_get_fmt,
 	.read_avail = ad7192_read_avail,
+	.read_avail_release_resource = ad7192_read_avail_release_res,
 	.attrs = &ad7192_attribute_group,
 	.validate_trigger = ad_sd_validate_trigger,
 	.update_scan_mode = ad7192_update_scan_mode,
@@ -1108,6 +1124,7 @@ static const struct iio_info ad7194_info = {
 	.write_raw = ad7192_write_raw,
 	.write_raw_get_fmt = ad7192_write_raw_get_fmt,
 	.read_avail = ad7192_read_avail,
+	.read_avail_release_resource = ad7192_read_avail_release_res,
 	.validate_trigger = ad_sd_validate_trigger,
 };
 
@@ -1116,6 +1133,7 @@ static const struct iio_info ad7195_info = {
 	.write_raw = ad7192_write_raw,
 	.write_raw_get_fmt = ad7192_write_raw_get_fmt,
 	.read_avail = ad7192_read_avail,
+	.read_avail_release_resource = ad7192_read_avail_release_res,
 	.attrs = &ad7195_attribute_group,
 	.validate_trigger = ad_sd_validate_trigger,
 	.update_scan_mode = ad7192_update_scan_mode,

-- 
2.47.0