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

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Message-ID: <CAMRc=MfcVAeEMrd61YeMuwmVYRxsZUoVeEKFvpeVaei+1RrYBQ@mail.gmail.com>
Date:   Fri, 2 Dec 2022 16:47:58 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nick Hainke <vincent@...temli.org>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v7 2/2] gpiolib: protect the GPIO device against being
 dropped while in use by user-space

On Fri, Dec 2, 2022 at 4:45 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Fri, Dec 02, 2022 at 04:04:44PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > 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@...aro.org>
> > [Nick: fixed a build failure with CDEV_V1 disabled]
>
> > Co-authored-by: Nick Hainke <vincent@...temli.org>
>
> 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