Re: [PATCH v7 2/2] gpiolib: protect the GPIO device against being dropped while in use by user-space

[Bartosz Golaszewski]

On Fri, Dec 2, 2022 at 4:45 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Fri, Dec 02, 2022 at 04:04:44PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> >
> > While any of the GPIO cdev syscalls is in progress, the kernel can call
> > gpiochip_remove() (for instance, when a USB GPIO expander is disconnected)
> > which will set gdev->chip to NULL after which any subsequent access will
> > cause a crash.
> >
> > To avoid that: use an RW-semaphore in which the syscalls take it for
> > reading (so that we don't needlessly prohibit the user-space from calling
> > syscalls simultaneously) while gpiochip_remove() takes it for writing so
> > that it can only happen once all syscalls return.
> >
> > 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>
> > [Nick: fixed a build failure with CDEV_V1 disabled]
>
> > Co-authored-by: Nick Hainke <vincent@xxxxxxxxxxxx>
>
> In Linux kernel there is no such tag. And in case you want to use
> Co-developed-by, you also need to add the respective SoB one.
>

Right, I forgot the tags got standardized. I will fix it when
applying. I'll fix it directly in the for-current branch and let it
cook again overnight. I'll then resend my PR tomorrow.

Bartosz