linux-kernel - Re: [PATCH] gpiolib: cdev: Don't access uninitialized descriptor

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Date:   Fri, 8 Jul 2022 15:31:28 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Dipen Patel <dipenp@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: cdev: Don't access uninitialized descriptor

On Fri, Jul 8, 2022 at 1:25 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> linereq_free() can be called from in the middle of errors, where the
> descriptor may be NULL for few lines. Don't access uninitialized
> descriptor pointer as it leads to kernel crash:
>
>     Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
>
>     [...]
>
>     Call trace:
>      linereq_free+0x54/0xb8
>      linereq_create+0x424/0x570
>      gpio_ioctl+0x94/0x640
>      __arm64_sys_ioctl+0xac/0xf0
>      invoke_syscall+0x44/0x100
>      el0_svc_common.constprop.3+0x6c/0xf0
>      do_el0_svc+0x2c/0xb8
>      el0_svc+0x20/0x60
>      el0t_64_sync_handler+0x98/0xc0
>      el0t_64_sync+0x170/0x174
>
> Fixes: 2068339a6c35 ("gpiolib: cdev: Add hardware timestamp clock type")
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/gpio/gpiolib-cdev.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index f5aa5f93342a..d3d1b5aed282 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -1460,11 +1460,13 @@ static ssize_t linereq_read(struct file *file,
>  static void linereq_free(struct linereq *lr)
>  {
>         unsigned int i;
> -       bool hte;
> +       bool hte = false;
>
>         for (i = 0; i < lr->num_lines; i++) {
> -               hte = !!test_bit(FLAG_EVENT_CLOCK_HTE,
> -                                &lr->lines[i].desc->flags);
> +               if (lr->lines[i].desc) {
> +                       hte = !!test_bit(FLAG_EVENT_CLOCK_HTE,
> +                                        &lr->lines[i].desc->flags);
> +               }
>                 edge_detector_stop(&lr->lines[i], hte);
>                 if (lr->lines[i].desc)
>                         gpiod_free(lr->lines[i].desc);
> --
> 2.31.1.272.g89b43f80a514
>

Hey Viresh!

Kent beat you to it with commit c8e27a4a5136e7230f9e4ffcf132705bf56864cc.

Bart