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From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Thu, 12 Jan 2023 10:01:00 +0100
Message-ID: <CAMRc=MfhVVN+W0Th8jdzTBHu6reFNpkm_cst3jMQZij0bDD=jQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/2] i2c: fortify the subsystem against user-space
 induced deadlocks
To:     Wolfram Sang <wsa@kernel.org>
Cc:     linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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On Thu, Dec 29, 2022 at 5:00 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Several subsystems in the kernel that export device files to user-space
> suffer from a bug where keeping an open file descriptor associated with
> this device file, unbinding the device from its driver and then calling
> any of the supported system calls on that file descriptor will result in
> either a crash or - as is the case with i2c - a deadlock.
>
> This behavior has been blamed on extensive usage of device resource
> management interfaces but it seems that devres has nothing to do with it,
> the problem would be the same whether using devres or freeing resources
> in .remove() that should survive the driver detach.
>
> Many subsystems already deal with this by implementing some kind of flags
> in the character device data together with locking preventing the
> user-space from dropping the subsystem data from under the open device.
>
> In i2c the deadlock comes from the fact that the function unregistering
> the adapter waits for a completion which will not be passed until all
> references to the character device are dropped.
>
> The first patch in this series is just a tweak of return values of the
> notifier callback. The second addresses the deadlock problem in a way
> similar to how we fixed this issue in the GPIO subystem. Details are in
> the commit message.
>
> v1 -> v2:
> - keep the device release callback and use it to free the IDR number
> - rebase on top of v6.2-rc1
>
> Bartosz Golaszewski (2):
>   i2c: dev: fix notifier return values
>   i2c: dev: don't allow user-space to deadlock the kernel
>
>  drivers/i2c/i2c-core-base.c |  26 ++-------
>  drivers/i2c/i2c-dev.c       | 112 +++++++++++++++++++++++++++++-------
>  include/linux/i2c.h         |   2 -
>  3 files changed, 96 insertions(+), 44 deletions(-)
>
> --
> 2.37.2
>

Hi Wolfram,

It's been two weeks without any comments on this series and over a
month since v1 so let me send a gentle ping on this.

Bart