[PATCH v5 2/5] iio: consumers: copy/release available info from producer to fix race

Matteo Martelli
2024-10-21T12:56:28Z

Consumers need to call the producer's read_avail_release_resource()
callback after reading producer's available info. To avoid a race
condition with the producer unregistration, change inkern
iio_channel_read_avail() so that it copies the available info from the
producer and immediately calls its release callback with info_exists
locked.

Also, modify the users of iio_read_avail_channel_raw() and
iio_read_avail_channel_attribute() to free the copied available buffers
after calling these functions. To let users free the copied buffer with
a cleanup pattern, also add a iio_read_avail_channel_attr_retvals()
consumer helper that is equivalent to iio_read_avail_channel_attribute()
but stores the available values in the returned variable.

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
---
drivers/iio/afe/iio-rescale.c | 8 +++
drivers/iio/dac/dpot-dac.c | 8 +++
drivers/iio/inkern.c | 99 ++++++++++++++++++++++++++++------
drivers/iio/multiplexer/iio-mux.c | 8 +++
drivers/power/supply/ingenic-battery.c | 22 +++++---
include/linux/iio/consumer.h | 28 +++++++++-
6 files changed, 147 insertions(+), 26 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 56e5913ab82d1c045c9ca27012008a4495502cbf..78bb86c291706748b4072a484532ad20c415ff9f 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -249,9 +249,17 @@ static int rescale_read_avail(struct iio_dev *indio_dev,
}
}

+static void rescale_read_avail_release_res(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ const int *vals, long mask)
+{
+ kfree(vals);
+}
+
static const struct iio_info rescale_info = {
.read_raw = rescale_read_raw,
.read_avail = rescale_read_avail,
+ .read_avail_release_resource = rescale_read_avail_release_res,
};

static ssize_t rescale_read_ext_info(struct iio_dev *indio_dev,
diff --git a/drivers/iio/dac/dpot-dac.c b/drivers/iio/dac/dpot-dac.c
index f36f10bfb6be7863a56b911b5f58671ef530c977..43d68e17fc3a5fca59fad6ccf818eeadfecdb8c1 100644
--- a/drivers/iio/dac/dpot-dac.c
+++ b/drivers/iio/dac/dpot-dac.c
@@ -108,6 +108,13 @@ static int dpot_dac_read_avail(struct iio_dev *indio_dev,
return -EINVAL;
}

+static void dpot_dac_read_avail_release_res(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ const int *vals, long mask)
+{
+ kfree(vals);
+}
+
static int dpot_dac_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int val, int val2, long mask)
@@ -125,6 +132,7 @@ static int dpot_dac_write_raw(struct iio_dev *indio_dev,
static const struct iio_info dpot_dac_info = {
.read_raw = dpot_dac_read_raw,
.read_avail = dpot_dac_read_avail,
+ .read_avail_release_resource = dpot_dac_read_avail_release_res,
.write_raw = dpot_dac_write_raw,
};

diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
index 7f325b3ed08fae6674245312cf8f57bb151006c0..7b87d1c57d6fd1258d254192835aa6cb9355f859 100644
--- a/drivers/iio/inkern.c
+++ b/drivers/iio/inkern.c
@@ -760,12 +760,56 @@ static int iio_channel_read_avail(struct iio_channel *chan,
if (!iio_channel_has_available(chan->channel, info))
return -EINVAL;

- if (iio_info->read_avail)
- return iio_info->read_avail(chan->indio_dev, chan->channel,
- vals, type, length, info);
+ if (iio_info->read_avail) {
+ const int *vals_tmp;
+ int ret;
+
+ ret = iio_info->read_avail(chan->indio_dev, chan->channel,
+ &vals_tmp, type, length, info);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * Copy the producer's avail buffer with lock_exists locked to
+ * avoid possible race with producer unregistration.
+ */
+ *vals = kmemdup_array(vals_tmp, *length, sizeof(int), GFP_KERNEL);
+ if (!*vals)
+ return -ENOMEM;
+
+ if (iio_info->read_avail_release_resource)
+ iio_info->read_avail_release_resource(
+ chan->indio_dev, chan->channel, vals_tmp, info);
+
+ return ret;
+ }
return -EINVAL;
}

+/*
+ * iio_channel_read_avail_retvals() is equivalent to iio_channel_read_avail()
+ * but stores the pointer to the buffer of available values in the returned
+ * variable. Since such buffer must be freed after use, this function lets the
+ * user declare a cleanup local variable, e.g.:
+ * const int *vals = __free(kfree) = iio_channel_read_avail_retvals(...);
+ */
+static const int *iio_channel_read_avail_retvals(struct iio_channel *chan,
+ int *type, int *length,
+ int *avail_type,
+ enum iio_chan_info_enum info)
+{
+ const int *vals;
+ int ret;
+
+ ret = iio_channel_read_avail(chan, &vals, type, length, info);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ *avail_type = ret;
+
+ return vals;
+}
+
int iio_read_avail_channel_attribute(struct iio_channel *chan,
const int **vals, int *type, int *length,
enum iio_chan_info_enum attribute)
@@ -780,6 +824,25 @@ int iio_read_avail_channel_attribute(struct iio_channel *chan,
}
EXPORT_SYMBOL_GPL(iio_read_avail_channel_attribute);

+const int *
+iio_read_avail_channel_attr_retvals(struct iio_channel *chan, int *type,
+ int *length, int *avail_type,
+ enum iio_chan_info_enum attribute)
+{
+ const int *vals;
+ int ret;
+
+ ret = iio_read_avail_channel_attribute(chan, &vals, type, length,
+ attribute);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ *avail_type = ret;
+
+ return vals;
+}
+EXPORT_SYMBOL_GPL(iio_read_avail_channel_attr_retvals);
+
int iio_read_avail_channel_raw(struct iio_channel *chan,
const int **vals, int *length)
{
@@ -789,9 +852,11 @@ int iio_read_avail_channel_raw(struct iio_channel *chan,
ret = iio_read_avail_channel_attribute(chan, vals, &type, length,
IIO_CHAN_INFO_RAW);

- if (ret >= 0 && type != IIO_VAL_INT)
+ if (ret >= 0 && type != IIO_VAL_INT) {
/* raw values are assumed to be IIO_VAL_INT */
+ kfree(*vals);
ret = -EINVAL;
+ }

return ret;
}
@@ -801,15 +866,16 @@ static int iio_channel_read_max(struct iio_channel *chan,
int *val, int *val2, int *type,
enum iio_chan_info_enum info)
{
- const int *vals;
int length;
- int ret;
+ int avail_type;

- ret = iio_channel_read_avail(chan, &vals, type, &length, info);
- if (ret < 0)
- return ret;
+ const int *vals __free(kfree) =
+ iio_channel_read_avail_retvals(chan, type, &length,
+ &avail_type, info);
+ if (IS_ERR(vals))
+ return PTR_ERR(vals);

- switch (ret) {
+ switch (avail_type) {
case IIO_AVAIL_RANGE:
switch (*type) {
case IIO_VAL_INT:
@@ -857,15 +923,16 @@ static int iio_channel_read_min(struct iio_channel *chan,
int *val, int *val2, int *type,
enum iio_chan_info_enum info)
{
- const int *vals;
int length;
- int ret;
+ int avail_type;

- ret = iio_channel_read_avail(chan, &vals, type, &length, info);
- if (ret < 0)
- return ret;
+ const int *vals __free(kfree) =
+ iio_channel_read_avail_retvals(chan, type, &length,
+ &avail_type, info);
+ if (IS_ERR(vals))
+ return PTR_ERR(vals);

- switch (ret) {
+ switch (avail_type) {
case IIO_AVAIL_RANGE:
switch (*type) {
case IIO_VAL_INT:
diff --git a/drivers/iio/multiplexer/iio-mux.c b/drivers/iio/multiplexer/iio-mux.c
index 2953403bef53bbe47a97a8ab1c475ed88d7f86d2..31345437784b01c5d6f8ea70263f4c2574388e7a 100644
--- a/drivers/iio/multiplexer/iio-mux.c
+++ b/drivers/iio/multiplexer/iio-mux.c
@@ -142,6 +142,13 @@ static int mux_read_avail(struct iio_dev *indio_dev,
return ret;
}

+static void mux_read_avail_release_res(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ const int *vals, long mask)
+{
+ kfree(vals);
+}
+
static int mux_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int val, int val2, long mask)
@@ -171,6 +178,7 @@ static int mux_write_raw(struct iio_dev *indio_dev,
static const struct iio_info mux_info = {
.read_raw = mux_read_raw,
.read_avail = mux_read_avail,
+ .read_avail_release_resource = mux_read_avail_release_res,
.write_raw = mux_write_raw,
};

diff --git a/drivers/power/supply/ingenic-battery.c b/drivers/power/supply/ingenic-battery.c
index 0a40f425c27723ccec49985b8b5e14a737b6a7eb..5d82c799ba5af3302bfcdfadb5f57adf6b12b353 100644
--- a/drivers/power/supply/ingenic-battery.c
+++ b/drivers/power/supply/ingenic-battery.c
@@ -6,12 +6,14 @@
* based on drivers/power/supply/jz4740-battery.c
*/

+#include <linux/cleanup.h>
#include <linux/iio/consumer.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/power_supply.h>
#include <linux/property.h>
+#include <linux/slab.h>

struct ingenic_battery {
struct device *dev;
@@ -62,8 +64,8 @@ static int ingenic_battery_get_property(struct power_supply *psy,
*/
static int ingenic_battery_set_scale(struct ingenic_battery *bat)
{
- const int *scale_raw;
- int scale_len, scale_type, best_idx = -1, best_mV, max_raw, i, ret;
+ int scale_len, scale_type, scale_avail_type;
+ int best_idx = -1, best_mV, max_raw, i, ret;
u64 max_mV;

ret = iio_read_max_channel_raw(bat->channel, &max_raw);
@@ -72,14 +74,18 @@ static int ingenic_battery_set_scale(struct ingenic_battery *bat)
return ret;
}

- ret = iio_read_avail_channel_attribute(bat->channel, &scale_raw,
- &scale_type, &scale_len,
- IIO_CHAN_INFO_SCALE);
- if (ret < 0) {
+ const int *scale_raw __free(kfree) =
+ iio_read_avail_channel_attr_retvals(bat->channel,
+ &scale_type,
+ &scale_len,
+ &scale_avail_type,
+ IIO_CHAN_INFO_SCALE);
+ if (IS_ERR(scale_raw)) {
dev_err(bat->dev, "Unable to read channel avail scale\n");
- return ret;
+ return PTR_ERR(scale_raw);
}
- if (ret != IIO_AVAIL_LIST || scale_type != IIO_VAL_FRACTIONAL_LOG2)
+ if (scale_avail_type != IIO_AVAIL_LIST ||
+ scale_type != IIO_VAL_FRACTIONAL_LOG2)
return -EINVAL;

max_mV = bat->info->voltage_max_design_uv / 1000;
diff --git a/include/linux/iio/consumer.h b/include/linux/iio/consumer.h
index 333d1d8ccb37f387fe531577ac5e0bfc7f752cec..188cc64609bd1fd8e0522e69f0b65a73b9b1606d 100644
--- a/include/linux/iio/consumer.h
+++ b/include/linux/iio/consumer.h
@@ -316,7 +316,7 @@ int iio_read_min_channel_raw(struct iio_channel *chan, int *val);
/**
* iio_read_avail_channel_raw() - read available raw values from a given channel
* @chan: The channel being queried.
- * @vals: Available values read back.
+ * @vals: Available values read back. Must be freed after use.
* @length: Number of entries in vals.
*
* Returns an error code, IIO_AVAIL_RANGE or IIO_AVAIL_LIST.
@@ -334,7 +334,7 @@ int iio_read_avail_channel_raw(struct iio_channel *chan,
/**
* iio_read_avail_channel_attribute() - read available channel attribute values
* @chan: The channel being queried.
- * @vals: Available values read back.
+ * @vals: Available values read back. Must be freed after use.
* @type: Type of values read back.
* @length: Number of entries in vals.
* @attribute: info attribute to be read back.
@@ -345,6 +345,30 @@ int iio_read_avail_channel_attribute(struct iio_channel *chan,
const int **vals, int *type, int *length,
enum iio_chan_info_enum attribute);

+
+/**
+ * iio_read_avail_channel_attr_retvals() - read available channel attr values
+ * @chan: The channel being queried.
+ * @type: Type of values read back.
+ * @length: Number of entries in vals.
+ * @avail_type: Available type of values read back
+ * (IIO_AVAIL_RANGE or IIO_AVAIL_LIST).
+ * @attribute: info attribute to be read back.
+ *
+ * This function is equivalent to iio_read_avail_channel_attribute() but stores
+ * the pointer to the buffer of available values in the returned variable.
+ * Since such buffer must be freed after use, this function lets the user
+ * declare a cleanup local variable, e.g.:
+ * const int *vals = __free(kfree) = iio_read_avail_channel_attr_retvals(...);
+ *
+ * Returns a pointer to negative errno on error otherwise returns the available
+ * values read back that must be freed after use.
+ */
+const int *
+iio_read_avail_channel_attr_retvals(struct iio_channel *chan, int *type,
+ int *length, int *avail_type,
+ enum iio_chan_info_enum attribute);
+
/**
* iio_get_channel_type() - get the type of a channel
* @channel: The channel being queried.

--
2.47.0