linux-kernel - Re: [PATCH][next][V2] gpio: sim: Fix dereference of free'd pointer config

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Date:   Tue, 27 Apr 2021 14:57:37 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next][V2] gpio: sim: Fix dereference of free'd pointer config

On Tue, Apr 27, 2021 at 2:20 PM Colin Ian King <colin.king@...onical.com> wrote:
>
> On 27/04/2021 13:11, Andy Shevchenko wrote:
> > On Tue, Apr 27, 2021 at 2:49 PM Colin King <colin.king@...onical.com> wrote:
> >>
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> The error return of config->id dereferences the kfree'd object config.
> >> Fix this by using a temporary variable for the id to avoid this issue.
> >
> > Thanks!
> > I'm wondering how I missed this... Nevertheless
> >
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> >
> >> Addresses-Coverity: ("Read from pointer aftyer free")
> >
> > after
> >
>
> Can that be fixed before applying rather me sending a V3?
>

No need, I'll add it and apply right away.

Bartosz

> >> Fixes: a49d14276ac4 ("gpio: sim: allocate IDA numbers earlier")
> >> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >> ---
> >> V2: Don't make id local to the if statement to improve coding style.
> >>     Thanks to Bartosz Golaszewski for this improvement suggestion.
> >> ---
> >>  drivers/gpio/gpio-sim.c | 8 +++++---
> >>  1 file changed, 5 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
> >> index 2e2e6399e453..b21541c0b700 100644
> >> --- a/drivers/gpio/gpio-sim.c
> >> +++ b/drivers/gpio/gpio-sim.c
> >> @@ -744,20 +744,22 @@ static struct config_item *
> >>  gpio_sim_config_make_item(struct config_group *group, const char *name)
> >>  {
> >>         struct gpio_sim_chip_config *config;
> >> +       int id;
> >>
> >>         config = kzalloc(sizeof(*config), GFP_KERNEL);
> >>         if (!config)
> >>                 return ERR_PTR(-ENOMEM);
> >>
> >> -       config->id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
> >> -       if (config->id < 0) {
> >> +       id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
> >> +       if (id < 0) {
> >>                 kfree(config);
> >> -               return ERR_PTR(config->id);
> >> +               return ERR_PTR(id);
> >>         }
> >>
> >>         config_item_init_type_name(&config->item, name,
> >>                                    &gpio_sim_chip_config_type);
> >>         config->num_lines = 1;
> >> +       config->id = id;
> >>         mutex_init(&config->lock);
> >>
> >>         return &config->item;
> >> --
> >> 2.30.2
> >>
> >
> >
>