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

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Date:   Sun, 31 Mar 2019 13:01:49 +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,

Thank you for the notification.

On 3/31/19 11:06 AM, Geert Uytterhoeven wrote:
> Hi Jacek,
> 
> 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?

> Moreover, this cannot happen, as pca9532_of_populate_pdata() already
> contains a similar check.

Right, I assumed this fixes a real problem and didn't spent too much
time investigating the whole context.. Lesson for the future.

> Kangjie: please stop submitting patches for missing checks, without
> investigating if the failures can actually happen. Thanks!
> 
>>> +                     return -EINVAL;
>>> +             devid = (int)of_id->data;
>>>        } else {
>>>                devid = id->driver_data;
>>>        }
>>
>>
>> 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.

-- 
Best regards,
Jacek Anaszewski