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

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Message-ID: <CA+U=Dsqti6mActFZ_1r4hxF5LqYRO=APriLwWb=fH19HdkirsQ@mail.gmail.com>
Date:   Sun, 7 Mar 2021 20:35:58 +0200
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: buffer: fix use-after-free for attached_buffers array

On Sun, Mar 7, 2021 at 2:54 PM Lars-Peter Clausen <lars@...afoo.de> wrote:
>
> 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.

That actually sounds like it fits beautifully ( the
iio_device_detach_buffers() name ).
Thanks for the hint.

I'll send a V2.
I didn't consider more on the renaming of iio_buffers_put() because I
was a bit stressed by the silliness of the use-after-free bug.

Thanks
Alex

>
> - Lars
>