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

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Message-ID: <b80db02b-c940-bc6b-a795-82cd9ff43a6b@canonical.com>
Date:   Tue, 27 Apr 2021 13:20:26 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "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 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?

>> 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
>>
> 
>