Re: [PATCH v5 1/2] gpiolib: cdev: fix NULL-pointer dereferences

[Kent Gibson <warthog618@xxxxxxxxx>]

On Thu, Dec 01, 2022 at 09:33:34AM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> 
> There are several places where we can crash the kernel by requesting
> lines, unbinding the GPIO device, then calling any of the system calls
> relevant to the GPIO character device's annonymous file descriptors:
> ioctl(), read(), poll().
> 
> While I observed it with the GPIO simulator, it will also happen for any
> of the GPIO devices that can be hot-unplugged - for instance any HID GPIO
> expander (e.g. CP2112).
> 
> This affects both v1 and v2 uAPI.
> 
> This fixes it partially by checking if gdev->chip is not NULL but it
> doesn't entirely remedy the situation as we still have a race condition
> in which another thread can remove the device after the check.
> 
> Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines")
> Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL")
> Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
> Fixes: a54756cb24ea ("gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL")
> Fixes: 7b8e00d98168 ("gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

As per v4, I'm fine with whole series, so

Reviewed-by: Kent Gibson <warthog618@xxxxxxxxx>

Cheers,
Kent.