linux-kernel - Re: [PATCH] iio: buffer: fix use-after-free for attached

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Message-ID: <a1ffef80-2f43-68bc-cb46-4f3bac326671@metafoo.de>
Date:   Sun, 7 Mar 2021 13:54:28 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Jonathan Cameron <jic23@...nel.org>,
        Alexandru Ardelean <ardeleanalex@...il.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: buffer: fix use-after-free for attached_buffers
 array

On 3/7/21 1:36 PM, Jonathan Cameron wrote:
> On Sat,  6 Mar 2021 18:47:10 +0200
> Alexandru Ardelean <ardeleanalex@...il.com> wrote:
>
>> Thanks to Lars for finding this.
>> The free of the 'attached_buffers' array should be done as late as
>> possible. This change moves it to iio_buffers_put(), which looks like
>> the best place for it, since it takes place right before the IIO device
>> data is free'd.
> It feels a bit wrong to do direct freeing of stuff in a _put() call
> given that kind of implies nothing will happen without some reference
> count dropping to 0.  We could think about renaming the function to
> something like
>
> iio_buffers_put_and_free_array() but is a bit long winded.
>
> Otherwise, I'm fine with this but want to let it sit on list a tiny bit
> longer before I take it as it's not totally trivial unlike the previous
> one.

Maybe to go with naming schema of iio_device_attach_buffer() call this 
function iio_device_detach_buffers(). We grab the reference in attach, 
and drop it in detach.

- Lars