Re: [PATCH v2 0/2] i2c: fortify the subsystem against user-space induced deadlocks

Bartosz Golaszewski
2023-01-12T09:06:48Z

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