linux-kernel - Re: [PATCH v6 19/24] iio: buffer: introduce support for attaching more IIO buffers

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Date:   Sun, 28 Feb 2021 09:29:01 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Cc:     Michael.Hennerich@...log.com, jic23@...nel.org, nuno.sa@...log.com,
        dragos.bogdan@...log.com
Subject: Re: [PATCH v6 19/24] iio: buffer: introduce support for attaching
 more IIO buffers

On 2/15/21 11:40 AM, Alexandru Ardelean wrote:
>   static ssize_t iio_show_scan_index(struct device *dev,
>   				   struct device_attribute *attr,
>   				   char *buf)
> @@ -1451,11 +1465,13 @@ static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
>   	iio_free_chan_devattr_list(&buffer->buffer_attr_list);
>   }
>   
> -int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> +int iio_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
>   {
> [...]
> +error_unwind_sysfs_and_mask:
> +	for (; unwind_idx >= 0; unwind_idx--) {
> +		buffer = iio_dev_opaque->attached_buffers[unwind_idx];
> +		__iio_buffer_free_sysfs_and_mask(buffer);
> +	}
> +	kfree(iio_dev_opaque->attached_buffers);
> +	return ret;
>   }
>   
> -void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> +void iio_buffers_free_sysfs_and_mask(struct iio_dev *indio_dev)
>   {
> [...]
> +	for (i = iio_dev_opaque->attached_buffers_cnt - 1; i >= 0; i--) {
> +		buffer = iio_dev_opaque->attached_buffers[i];
> +		__iio_buffer_free_sysfs_and_mask(buffer);
> +	}
> +
> +	kfree(iio_dev_opaque->attached_buffers);
>   }
> [...]
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 1d500ea246af..f7f785431106 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1583,7 +1583,7 @@ static void iio_dev_release(struct device *device)
>   	iio_device_unregister_eventset(indio_dev);
>   	iio_device_unregister_sysfs(indio_dev);
>   
> -	iio_buffer_put(indio_dev->buffer);
> +	iio_buffers_put(indio_dev);
We do call kfree(iio_dev_opaque->attached_buffers) before we get here. I 
think we need to keep the array around, otherwise we end of up with a 
use after free.