patch "iio: triggered-buffer: prevent possible freeing of wrong buffer" added to char-misc-linus

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    iio: triggered-buffer: prevent possible freeing of wrong buffer

to my char-misc git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


From bce61476dc82f114e24e9c2e11fb064781ec563c Mon Sep 17 00:00:00 2001
From: David Lechner <dlechner@baylibre.com>
Date: Tue, 31 Oct 2023 16:05:19 -0500
Subject: iio: triggered-buffer: prevent possible freeing of wrong buffer

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.

As per discussion in the review thread, we may want to deal with multiple
triggers per device, but this is a fix for the issue in the meantime and
any such support would be unlikely to be suitable for a backport.

Fixes: ee708e6baacd ("iio: buffer: introduce support for attaching more IIO buffers")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Acked-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20231031210521.1661552-1-dlechner@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.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;
-- 
2.43.0