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

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Date:   Tue, 12 Oct 2021 10:55:52 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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, 2021-10-12 at 23:48 +0300, Andy Shevchenko wrote:
> 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.

Not really,

> What's needed additionally is to change
> 
> - unwind_idx = iio_dev_opaque->attached_buffers_cnt - 1;
> + unwind_idx = i;

You left out that 'additional change' above from your reply.

> Of course not. See above. The usual pattern is
> 
>   while (i--)
>     do_clean_item(i);

Of course, but that's not what you replied.
I was merely pointing out that your reply included a logic change
converting a loop from for to while.

cheers, Joe