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

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Message-ID: <CA+U=DsrhojhamxY6da7CSu79pkAnF=nHPk3H=xAbkZmtLozx2g@mail.gmail.com>
Date:   Sun, 28 Feb 2021 19:46:51 +0200
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Nuno Sá <nuno.sa@...log.com>,
        "Bogdan, Dragos" <dragos.bogdan@...log.com>
Subject: Re: [PATCH v6 19/24] iio: buffer: introduce support for attaching
 more IIO buffers

On Sun, Feb 28, 2021 at 10:31 AM Lars-Peter Clausen <lars@...afoo.de> wrote:
>
> 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.
>

Good catch.
Will send an update here.