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

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

[David Lechner]

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

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

[Nuno Sá]

On Tue, 2023-10-31 at 16:05 -0500, David Lechner wrote:
> 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;
> +

Hmmm, good catch! But I think this is just workarounding the real problem
because like this, you can only have a triggered buffer by device. This should
be fine as we don't really have any multi buffer user so far but ideally it
should be possible.

Long term we might want to think about moving 'pollfunc' to be a per buffer
thing. Not sure how much trouble that would be given that a trigger is also per
device and I don't know if it would make sense to have a trigger per buffer?!
Ideally, given the multi buffer concept, I would say it makes sense but it might
be difficult to accomplish. So better to think about it only if there's a real
usecase for it. 

On thing that I guess it could be done is to change the triggered API so it
returns a buffer and so iio_triggered_buffer_cleanup() would also get a pointer
to the buffer it allocated (similar to what DMA buffer's are doing). But that's
indeed also bigger change... Bahh, I'm likely over complicating things for now.
Fell free to:

Acked-by: Nuno Sa <nuno.sa@analog.com>

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

[David Lechner]

On Thu, Nov 2, 2023 at 3:59 AM Nuno Sá <noname.nuno@gmail.com> wrote:
>
> On Tue, 2023-10-31 at 16:05 -0500, David Lechner wrote:
> > 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;
> > +
>
> Hmmm, good catch! But I think this is just workarounding the real problem

Yes, I could have done a better job explaining my reason for this fix.
It seemed like the simplest fix that could be easily backported to
stable kernels. And then we can look at removing the legacy field
completely in the future.

> because like this, you can only have a triggered buffer by device. This should
> be fine as we don't really have any multi buffer user so far but ideally it
> should be possible.
>
> Long term we might want to think about moving 'pollfunc' to be a per buffer
> thing. Not sure how much trouble that would be given that a trigger is also per
> device and I don't know if it would make sense to have a trigger per buffer?!
> Ideally, given the multi buffer concept, I would say it makes sense but it might
> be difficult to accomplish. So better to think about it only if there's a real
> usecase for it.
>
> On thing that I guess it could be done is to change the triggered API so it
> returns a buffer and so iio_triggered_buffer_cleanup() would also get a pointer
> to the buffer it allocated (similar to what DMA buffer's are doing). But that's
> indeed also bigger change... Bahh, I'm likely over complicating things for now.

This sounds very much like the work I am doing on SPI Engine offload
support - having a trigger associated with a buffer. So maybe
something will come out of that. ¯\_(ツ)_/¯

> Fell free to:
>
> Acked-by: Nuno Sa <nuno.sa@analog.com>
>
>

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

[Jonathan Cameron]

On Thu, 2 Nov 2023 09:53:13 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On Thu, Nov 2, 2023 at 3:59 AM Nuno Sá <noname.nuno@gmail.com> wrote:
> >
> > On Tue, 2023-10-31 at 16:05 -0500, David Lechner wrote:  
> > > 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;
> > > +  
> >
> > Hmmm, good catch! But I think this is just workarounding the real problem  
> 
> Yes, I could have done a better job explaining my reason for this fix.
> It seemed like the simplest fix that could be easily backported to
> stable kernels. And then we can look at removing the legacy field
> completely in the future.
> 
> > because like this, you can only have a triggered buffer by device. This should
> > be fine as we don't really have any multi buffer user so far but ideally it
> > should be possible.

So far multibufferred devices have always been for cases where triggers don't make
sense (devices with multiple hardware fifos that run out of step or where a single
fifo is filled unevenly from different sensors, or big complex dma based devices
where the trigger concept doesn't map at all.)

I agree that it sort of make sense to make the trigger per buffer, but in practice
I'm not sure on what sort of device will need it. Mind you, I guess you hit this
in practice which rather implies something does!

> >
> > Long term we might want to think about moving 'pollfunc' to be a per buffer
> > thing. Not sure how much trouble that would be given that a trigger is also per
> > device and I don't know if it would make sense to have a trigger per buffer?!
> > Ideally, given the multi buffer concept, I would say it makes sense but it might
> > be difficult to accomplish. So better to think about it only if there's a real
> > usecase for it.
> >
> > On thing that I guess it could be done is to change the triggered API so it
> > returns a buffer and so iio_triggered_buffer_cleanup() would also get a pointer
> > to the buffer it allocated (similar to what DMA buffer's are doing). But that's
> > indeed also bigger change... Bahh, I'm likely over complicating things for now.  
> 
> This sounds very much like the work I am doing on SPI Engine offload
> support - having a trigger associated with a buffer. So maybe
> something will come out of that. ¯\_(ツ)_/¯

Ah. I guess if the trigger is being used to route things out of sight of software that
might be a case where we do need multiple triggers per device...

Doesn't sound 'too' hard to make work and we'll end up with similar case to buffers
where
iio_deviceX/current_trigger maps to the one for buffer0 so no ABI breakage, just new
toys to play with.
> 
> > Fell free to:
> >
> > Acked-by: Nuno Sa <nuno.sa@analog.com>
> >
> >  
Applied with a note that we may revisit adding multiple triggers support in future
but that is unlikely to be suitable for a backport as it's a new feature.

Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan