linux-kernel - Re: [PATCH] i2c: core: fix potential use-after-free on adapter removal

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Message-ID: <YquFY50LfsezqrVn@shikoro>
Date:   Thu, 16 Jun 2022 21:32:51 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: core: fix potential use-after-free on adapter
 removal

Hi Michał,

> I looked briefly at the kobject machinery and it seems to ignore module
> dependencies. So while both approaches might work, I'd usually reverse

Thanks for checking!

> the order the init code is using: in this case module_get+device_get,
> so on release: device_put+module_put. I don't know what keeps the kernel

I agree this is good style. I'll add a comment why we reverse the order.
This will be also good to avoid regressions.

> from unloading the module after module_put() and before the function
> returns, but I assume that would blow up for both patches.

Yes. There are other users in the kernel doing it like this (RTC and
regmap IIRC), so I think problems would have become visible by then.

Thank you for your help!

   Wolfram


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