iio: bmc150-accel-core: Fix unsafe buffer attributes

The iio_triggered_buffer_setup_ext() was changed by
commit 15097c7 ("iio: buffer: wrap all buffer attributes into iio_dev_attr")
to silently expect that all attributes given in buffer_attrs array are
device-attributes. This expectation was not forced by the API - and some
drivers did register attributes created by IIO_CONST_ATTR().

The added attribute "wrapping" does not copy the pointer to stored
string constant and when the sysfs file is read the kernel will access
to invalid location.

Change the IIO_CONST_ATTRs from the driver to IIO_DEVICE_ATTR in order
to prevent the invalid memory access.

Signed-off-by: Matti Vaittinen <[email protected]>
Fixes: 15097c7 ("iio: buffer: wrap all buffer attributes into iio_dev_attr")
Link: https://lore.kernel.org/r/cf8a56658fc38db8bed64f456d898f5ad5a2814f.1664782676.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <[email protected]>

Author: M-Vaittinen

drivers/iio/accel/bmc150-accel-core.c

@@ -925,17 +925,30 @@ static const struct iio_chan_spec_ext_info bmc150_accel_ext_info[] = {
 	{ }
 };
 
-static IIO_CONST_ATTR(hwfifo_watermark_min, "1");
-static IIO_CONST_ATTR(hwfifo_watermark_max,
-		      __stringify(BMC150_ACCEL_FIFO_LENGTH));
+static ssize_t hwfifo_watermark_min_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	return sysfs_emit(buf, "%s\n", "1");
+}
+
+static ssize_t hwfifo_watermark_max_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	return sysfs_emit(buf, "%s\n", __stringify(BMC150_ACCEL_FIFO_LENGTH));
+}
+
+static IIO_DEVICE_ATTR_RO(hwfifo_watermark_min, 0);
+static IIO_DEVICE_ATTR_RO(hwfifo_watermark_max, 0);
 static IIO_DEVICE_ATTR(hwfifo_enabled, S_IRUGO,
 		       bmc150_accel_get_fifo_state, NULL, 0);
 static IIO_DEVICE_ATTR(hwfifo_watermark, S_IRUGO,
 		       bmc150_accel_get_fifo_watermark, NULL, 0);
 
 static const struct attribute *bmc150_accel_fifo_attributes[] = {
-	&iio_const_attr_hwfifo_watermark_min.dev_attr.attr,
-	&iio_const_attr_hwfifo_watermark_max.dev_attr.attr,
+	&iio_dev_attr_hwfifo_watermark_min.dev_attr.attr,
+	&iio_dev_attr_hwfifo_watermark_max.dev_attr.attr,
 	&iio_dev_attr_hwfifo_watermark.dev_attr.attr,
 	&iio_dev_attr_hwfifo_enabled.dev_attr.attr,
 	NULL,