[PATCH 1/2] iio: consumers: ensure read buffers for labels and ext_info are page aligned

[Matteo Martelli <matteomartelli3@gmail.com>]

Attributes of iio providers are exposed via sysfs. Typically, providers
pass attribute values to the iio core, which handles formatting and
printing to sysfs. However, some attributes, such as labels or extended
info, are directly formatted and printed to sysfs by provider drivers
using sysfs_emit() and sysfs_emit_at(). These helpers assume the read
buffer, allocated by sysfs fop, is page-aligned. When these attributes
are accessed by consumer drivers, the read buffer is allocated by the
consumer and may not be page-aligned, leading to failures in the
provider's callback that utilizes sysfs_emit*.

Add a check to ensure that read buffers for labels and external info
attributes are page-aligned. Update the prototype documentation as well.

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
---
 drivers/iio/inkern.c         | 11 +++++++++++
 include/linux/iio/consumer.h |  4 ++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
index 7f325b3ed08fae6674245312cf8f57bb151006c0..63707ed98e1d7aca1e446122bbf69c85c0dd06a2 100644
--- a/drivers/iio/inkern.c
+++ b/drivers/iio/inkern.c
@@ -7,6 +7,7 @@
 #include <linux/err.h>
 #include <linux/export.h>
 #include <linux/minmax.h>
+#include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/property.h>
 #include <linux/slab.h>
@@ -989,6 +990,11 @@ ssize_t iio_read_channel_ext_info(struct iio_channel *chan,
 {
 	const struct iio_chan_spec_ext_info *ext_info;
 
+	if (!buf || offset_in_page(buf)) {
+		pr_err("iio: invalid ext_info read buffer\n");
+		return -EINVAL;
+	}
+
 	ext_info = iio_lookup_ext_info(chan, attr);
 	if (!ext_info)
 		return -EINVAL;
@@ -1014,6 +1020,11 @@ EXPORT_SYMBOL_GPL(iio_write_channel_ext_info);
 
 ssize_t iio_read_channel_label(struct iio_channel *chan, char *buf)
 {
+	if (!buf || offset_in_page(buf)) {
+		pr_err("iio: invalid label read buffer\n");
+		return -EINVAL;
+	}
+
 	return do_iio_read_channel_label(chan->indio_dev, chan->channel, buf);
 }
 EXPORT_SYMBOL_GPL(iio_read_channel_label);
diff --git a/include/linux/iio/consumer.h b/include/linux/iio/consumer.h
index 333d1d8ccb37f387fe531577ac5e0bfc7f752cec..6a44796164792b2dd930f8168b14de327a80a6f7 100644
--- a/include/linux/iio/consumer.h
+++ b/include/linux/iio/consumer.h
@@ -418,7 +418,7 @@ unsigned int iio_get_channel_ext_info_count(struct iio_channel *chan);
  * @chan:		The channel being queried.
  * @attr:		The ext_info attribute to read.
  * @buf:		Where to store the attribute value. Assumed to hold
- *			at least PAGE_SIZE bytes.
+ *			at least PAGE_SIZE bytes and to be aligned at PAGE_SIZE.
  *
  * Returns the number of bytes written to buf (perhaps w/o zero termination;
  * it need not even be a string), or an error code.
@@ -445,7 +445,7 @@ ssize_t iio_write_channel_ext_info(struct iio_channel *chan, const char *attr,
  * iio_read_channel_label() - read label for a given channel
  * @chan:		The channel being queried.
  * @buf:		Where to store the attribute value. Assumed to hold
- *			at least PAGE_SIZE bytes.
+ *			at least PAGE_SIZE bytes and to be aligned at PAGE_SIZE.
  *
  * Returns the number of bytes written to buf, or an error code.
  */

-- 
2.47.0