linux-kernel - Re: [PATCH v3] i2c: dev: don't allow user-space to deadlock the kernel

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Message-ID: <CAMRc=Mdz_+_MDJAjkXWa2P8FM8i6XPMAVQ-xTUtZDXfD-RBo_w@mail.gmail.com>
Date:   Mon, 6 Feb 2023 19:01:11 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3] i2c: dev: don't allow user-space to deadlock the kernel

On Mon, Feb 6, 2023 at 4:51 PM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> Hello,
>
> ah, this is the mail I missed before.
>
> On Wed, Jan 25, 2023 at 11:11:59PM +0100, Wolfram Sang wrote:
> >
> > > So, this code handled all my stress-testing well so far. I'll try to
> > > think of some more ideas until this evening, but likely I will apply it
> > > later. Nonetheless, more review eyes are still welcome!
> >
> > Ah yes, I now recalled why I had the gut feeling that this solution is
> > not complete. See this mail thread from 2015:
> >
> > https://lkml.iu.edu/hypermail/linux/kernel/1501.2/01700.html
> >
> > There are still drivers using i2c_del_adapter()+kfree(), so removing the
> > completion could cause use-after-free there, or?
>
> There is also a strange construct in spi that I understand at one point
> in time, but I failed to swap it in quickly. It's about commit
> 794aaf01444d4e765e2b067cba01cc69c1c68ed9. I think there should be a
> nicer solution than to track if the controller was allocated using devm,
> but I don't remember the details. But before addressing the i2c problem
> it might be worth to invest some time into that spi issue to not make
> the same mistake for i2c.
>

Yeah, I've seen these constructs before elsewhere... Sadly, we have
workarounds upon workarounds within workarounds chased by other
workarounds due to this issue.

Bart