[PATCH] iio: triggered-buffer: prevent possible freeing of wrong buffer

[David Lechner <dlechner@baylibre.com>]

Commit ee708e6baacd ("iio: buffer: introduce support for attaching more
IIO buffers") introduced support for multiple buffers per indio_dev but
left indio_dev->buffer for a few legacy use cases.

In the case of the triggered buffer, iio_triggered_buffer_cleanup()
still assumes that indio_dev->buffer points to the buffer allocated by
iio_triggered_buffer_setup_ext(). However, since
iio_triggered_buffer_setup_ext() now calls iio_device_attach_buffer()
to attach the buffer, indio_dev->buffer will only point to the buffer
allocated by iio_device_attach_buffer() if it the first buffer attached.

This adds a check to make sure that no other buffer has been attached
yet to ensure that indio_dev->buffer will be assigned when
iio_device_attach_buffer() is called.

Fixes: ee708e6baacd ("iio: buffer: introduce support for attaching more IIO buffers")
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 drivers/iio/buffer/industrialio-triggered-buffer.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/iio/buffer/industrialio-triggered-buffer.c b/drivers/iio/buffer/industrialio-triggered-buffer.c
index c7671b1f5ead..c06515987e7a 100644
--- a/drivers/iio/buffer/industrialio-triggered-buffer.c
+++ b/drivers/iio/buffer/industrialio-triggered-buffer.c
@@ -46,6 +46,16 @@ int iio_triggered_buffer_setup_ext(struct iio_dev *indio_dev,
 	struct iio_buffer *buffer;
 	int ret;
 
+	/*
+	 * iio_triggered_buffer_cleanup() assumes that the buffer allocated here
+	 * is assigned to indio_dev->buffer but this is only the case if this
+	 * function is the first caller to iio_device_attach_buffer(). If
+	 * indio_dev->buffer is already set then we can't proceed otherwise the
+	 * cleanup function will try to free a buffer that was not allocated here.
+	 */
+	if (indio_dev->buffer)
+		return -EADDRINUSE;
+
 	buffer = iio_kfifo_allocate();
 	if (!buffer) {
 		ret = -ENOMEM;
-- 
2.42.0