linux-kernel - Re: [PATCH] iio: buffer: Fix double-free in iio_buffers_alloc_sysfs_and

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Date:   Tue, 12 Oct 2021 23:48:46 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Alexandru Ardelean <ardeleanalex@...il.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH] iio: buffer: Fix double-free in iio_buffers_alloc_sysfs_and_mask()

On Tue, Oct 12, 2021 at 8:43 PM Joe Perches <joe@...ches.com> wrote:
>
> On Tue, 2021-10-12 at 23:30 +0300, Andy Shevchenko wrote:
> > On Tue, Oct 12, 2021 at 2:37 PM Alexandru Ardelean
> > <ardeleanalex@...il.com> wrote:
> > >
> > > On Tue, Oct 12, 2021 at 12:18 PM Yang Yingliang
> > > <yangyingliang@...wei.com> wrote:
> > > >
> > > > When __iio_buffer_alloc_sysfs_and_mask() failed, 'unwind_idx' should be
> > > > set to 'i - 1' to prevent double-free when cleanup resources.
> []
> >
> > I prefer to see
> >
> > - for (; unwind_idx >= 0; unwind_idx--) {
> > + while (unwind_idx--)
>
> Not the same code as unwind_idx would be decremented before entering
> the code block.

It's kinda cryptic what you are pointing out.

What's needed additionally is to change

- unwind_idx = iio_dev_opaque->attached_buffers_cnt - 1;
+ unwind_idx = i;

> You'd want
>
>         do {
>                 ...
>         } while (unwind_idx--);

Of course not. See above. The usual pattern is

  while (i--)
    do_clean_item(i);

-- 
With Best Regards,
Andy Shevchenko