driver: iio: add missing checks on iio_info's callback access

Some callbacks from iio_info structure are accessed without any check, so
if a driver doesn't implement them trying to access the corresponding
sysfs entries produce a kernel oops such as:

[ 2203.527791] Unable to handle kernel NULL pointer dereference at virtual address 00000000 when execute
[...]
[ 2203.783416] Call trace:
[ 2203.783429]  iio_read_channel_info_avail from dev_attr_show+0x18/0x48
[ 2203.789807]  dev_attr_show from sysfs_kf_seq_show+0x90/0x120
[ 2203.794181]  sysfs_kf_seq_show from seq_read_iter+0xd0/0x4e4
[ 2203.798555]  seq_read_iter from vfs_read+0x238/0x2a0
[ 2203.802236]  vfs_read from ksys_read+0xa4/0xd4
[ 2203.805385]  ksys_read from ret_fast_syscall+0x0/0x54
[ 2203.809135] Exception stack(0xe0badfa8 to 0xe0badff0)
[ 2203.812880] dfa0:                   00000003 b6f10f80 00000003 b6eab000 00020000 00000000
[ 2203.819746] dfc0: 00000003 b6f10f80 7ff00000 00000003 00000003 00000000 00020000 00000000
[ 2203.826619] dfe0: b6e1bc88 bed80958 b6e1bc94 b6e1bcb0
[ 2203.830363] Code: bad PC value
[ 2203.832695] ---[ end trace 0000000000000000 ]---
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Link: https://lore.kernel.org/r/20240530-iio-core-fix-segfault-v3-1-8b7cd2a03773@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-core.c

@@ -758,9 +758,11 @@ static ssize_t iio_read_channel_info(struct device *dev,
 							INDIO_MAX_RAW_ELEMENTS,
 							vals, &val_len,
 							this_attr->address);
-	else
+	else if (indio_dev->info->read_raw)
 		ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
 				    &vals[0], &vals[1], this_attr->address);
+	else
+		return -EINVAL;
 
 	if (ret < 0)
 		return ret;
@@ -842,6 +844,9 @@ static ssize_t iio_read_channel_info_avail(struct device *dev,
 	int length;
 	int type;
 
+	if (!indio_dev->info->read_avail)
+		return -EINVAL;
+
 	ret = indio_dev->info->read_avail(indio_dev, this_attr->c,
 					  &vals, &type, &length,
 					  this_attr->address);

drivers/iio/industrialio-event.c

@@ -285,6 +285,9 @@ static ssize_t iio_ev_state_store(struct device *dev,
 	if (ret < 0)
 		return ret;
 
+	if (!indio_dev->info->write_event_config)
+		return -EINVAL;
+
 	ret = indio_dev->info->write_event_config(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr), val);
@@ -300,6 +303,9 @@ static ssize_t iio_ev_state_show(struct device *dev,
 	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
 	int val;
 
+	if (!indio_dev->info->read_event_config)
+		return -EINVAL;
+
 	val = indio_dev->info->read_event_config(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr));
@@ -318,6 +324,9 @@ static ssize_t iio_ev_value_show(struct device *dev,
 	int val, val2, val_arr[2];
 	int ret;
 
+	if (!indio_dev->info->read_event_value)
+		return -EINVAL;
+
 	ret = indio_dev->info->read_event_value(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr), iio_ev_attr_info(this_attr),

drivers/iio/inkern.c

@@ -543,6 +543,7 @@ EXPORT_SYMBOL_GPL(devm_iio_channel_get_all);
 static int iio_channel_read(struct iio_channel *chan, int *val, int *val2,
 			    enum iio_chan_info_enum info)
 {
+	const struct iio_info *iio_info = chan->indio_dev->info;
 	int unused;
 	int vals[INDIO_MAX_RAW_ELEMENTS];
 	int ret;
@@ -554,15 +555,18 @@ static int iio_channel_read(struct iio_channel *chan, int *val, int *val2,
 	if (!iio_channel_has_info(chan->channel, info))
 		return -EINVAL;
 
-	if (chan->indio_dev->info->read_raw_multi) {
-		ret = chan->indio_dev->info->read_raw_multi(chan->indio_dev,
-					chan->channel, INDIO_MAX_RAW_ELEMENTS,
-					vals, &val_len, info);
+	if (iio_info->read_raw_multi) {
+		ret = iio_info->read_raw_multi(chan->indio_dev,
+					       chan->channel,
+					       INDIO_MAX_RAW_ELEMENTS,
+					       vals, &val_len, info);
 		*val = vals[0];
 		*val2 = vals[1];
+	} else if (iio_info->read_raw) {
+		ret = iio_info->read_raw(chan->indio_dev,
+					 chan->channel, val, val2, info);
 	} else {
-		ret = chan->indio_dev->info->read_raw(chan->indio_dev,
-					chan->channel, val, val2, info);
+		return -EINVAL;
 	}
 
 	return ret;
@@ -750,11 +754,15 @@ static int iio_channel_read_avail(struct iio_channel *chan,
 				  const int **vals, int *type, int *length,
 				  enum iio_chan_info_enum info)
 {
+	const struct iio_info *iio_info = chan->indio_dev->info;
+
 	if (!iio_channel_has_available(chan->channel, info))
 		return -EINVAL;
 
-	return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
-						 vals, type, length, info);
+	if (iio_info->read_avail)
+		return iio_info->read_avail(chan->indio_dev, chan->channel,
+					    vals, type, length, info);
+	return -EINVAL;
 }
 
 int iio_read_avail_channel_attribute(struct iio_channel *chan,
@@ -917,8 +925,12 @@ EXPORT_SYMBOL_GPL(iio_get_channel_type);
 static int iio_channel_write(struct iio_channel *chan, int val, int val2,
 			     enum iio_chan_info_enum info)
 {
-	return chan->indio_dev->info->write_raw(chan->indio_dev,
-						chan->channel, val, val2, info);
+	const struct iio_info *iio_info = chan->indio_dev->info;
+
+	if (iio_info->write_raw)
+		return iio_info->write_raw(chan->indio_dev,
+					   chan->channel, val, val2, info);
+	return -EINVAL;
 }
 
 int iio_write_channel_attribute(struct iio_channel *chan, int val, int val2,