Re: [PATCH] iio: buffer: hold a reference while DMA-BUF is attached

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 04 Nov 2026 17:50:01 +0800
Yaohan Li <shunsheng1218@gmail.com> wrote:

> iio_buffer_attach_dmabuf() stores an IIO buffer pointer in the DMA-BUF
> attachment without taking a buffer reference. A delayed DMA fence
> completion can release the attachment after the IIO device has been
> unbound and its buffer freed. The release callback then dereferences
> the stale buffer while detaching the DMA-BUF.
> 
> Take a reference when storing the buffer in the attachment, and drop
> it after the final detach or when the attach operation fails. This
> keeps the buffer alive for the asynchronous completion path.
> 
> A KASAN-enabled test with a DMA-BUF-capable IIO test device reproduced
> the use-after-free on the unmodified kernel. The same delayed
> completion sequence produced no report with the change applied.
> 
> Fixes: 3e26d9f08fbe0 ("iio: core: Add new DMABUF interface infrastructure")
> Assisted-by: ZCode:GLM-4

The guidance on these tags change recently. Now the preference is
for a brief explanation of how the LLM was used under the ---

This seems reasonable to me but there are others who know the
IIO dma buffer stuff better that I do, so I'll wait for them
to take a look

Thanks,

Jonathan

> Signed-off-by: Yaohan Li <shunsheng1218@gmail.com>
> ---
>  drivers/iio/industrialio-buffer.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 4294101810fd7..bfa6d19471126 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -1597,6 +1597,8 @@ static void iio_buffer_dmabuf_release(struct kref *ref)
>  
>  	buffer->access->detach_dmabuf(buffer, priv->block);
>  
> +	iio_buffer_put(buffer);
> +
>  	dma_buf_detach(attach->dmabuf, attach);
>  	dma_buf_put(dmabuf);
>  	kfree(priv);
> @@ -1741,7 +1743,13 @@ static int iio_buffer_attach_dmabuf(struct iio_dev_buffer_pair *ib,
>  	}
>  
>  	kref_init(&priv->ref);
> -	priv->buffer = buffer;
> +	/*
> +	 * Hold a reference for the asynchronous dmabuf completion path
> +	 * (iio_buffer_cleanup() -> iio_buffer_dmabuf_put() may run from a
> +	 * work item after the device has been unbound); released in
> +	 * iio_buffer_dmabuf_release().
> +	 */
> +	priv->buffer = iio_buffer_get(buffer);
>  	priv->attach = attach;
>  	attach->importer_priv = priv;
>  
> @@ -1789,6 +1797,7 @@ static int iio_buffer_attach_dmabuf(struct iio_dev_buffer_pair *ib,
>  err_dmabuf_put:
>  	dma_buf_put(dmabuf);
>  err_free_priv:
> +	iio_buffer_put(priv->buffer);
>  	kfree(priv);
>  
>  	return err;