linux-kernel - Re: [PATCH] leds: fix a potential NULL pointer dereference

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Date:   Tue, 2 Apr 2019 20:48:05 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Kangjie Lu <kjlu@....edu>, pakki001@....edu,
        Riku Voipio <riku.voipio@....fi>, Pavel Machek <pavel@....cz>,
        linux-leds@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] leds: fix a potential NULL pointer dereference

Hi Geert,

On 4/1/19 9:08 AM, Geert Uytterhoeven wrote:
> Hi Jacek,
> 
> On Sun, Mar 31, 2019 at 1:01 PM Jacek Anaszewski
> <jacek.anaszewski@...il.com> wrote:
>> On 3/31/19 11:06 AM, Geert Uytterhoeven wrote:
>> On Sun, Mar 10, 2019 at 9:40 PM Jacek Anaszewski
>>> <jacek.anaszewski@...il.com> wrote:
>>>> On 3/9/19 7:04 AM, Kangjie Lu wrote:
>>>>> In case of_match_device cannot find a match, the fixes returns
>>>>> -EINVAL to avoid NULL pointer dereference.
>>>>>
>>>>> Signed-off-by: Kangjie Lu <kjlu@....edu>
>>>>> ---
>>>>>     drivers/leds/leds-pca9532.c | 8 ++++++--
>>>>>     1 file changed, 6 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/leds/leds-pca9532.c b/drivers/leds/leds-pca9532.c
>>>>> index 7fea18b0c15d..4b0335591728 100644
>>>>> --- a/drivers/leds/leds-pca9532.c
>>>>> +++ b/drivers/leds/leds-pca9532.c
>>>>> @@ -513,6 +513,7 @@ static int pca9532_probe(struct i2c_client *client,
>>>>>         const struct i2c_device_id *id)
>>>>>     {
>>>>>         int devid;
>>>>> +     const struct of_device_id *of_id;
>>>>>         struct pca9532_data *data = i2c_get_clientdata(client);
>>>>>         struct pca9532_platform_data *pca9532_pdata =
>>>>>                         dev_get_platdata(&client->dev);
>>>>> @@ -528,8 +529,11 @@ static int pca9532_probe(struct i2c_client *client,
>>>>>                         dev_err(&client->dev, "no platform data\n");
>>>>>                         return -EINVAL;
>>>>>                 }
>>>>> -             devid = (int)(uintptr_t)of_match_device(
>>>>> -                     of_pca9532_leds_match, &client->dev)->data;
>>>>> +             of_id = of_match_device(of_pca9532_leds_match,
>>>>> +                             &client->dev);
>>>>> +             if (unlikely(!of_id))
>>>
>>> Use of unlikey() is frowned upon.
>>
>> What do you mean? Can you give some reference?
> 
> I have more memories of this being discussed, but I could find only
> https://lwn.net/Articles/420019/

Thanks!

> It may be useful for some heavily used core code, but not in most drivers
> or uncritical code like probe paths, due to:
>    - many people getting it wrong,
>    - usually it doesn't make any difference at all.
> 
>>>> Applied to the for-5.2 branch of linux-leds.git.
>>>
>>> And also as a fix for v5.1...
>>
>> Yes, but it had been in linux-next for almost two weeks before that.
> 
> Sorry, I only noticed when it got upstream.

No problem.

-- 
Best regards,
Jacek Anaszewski