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Subject: Re: [PATCH] media: rcar-vin: fix a potential NULL pointer dereference
To:     =?UTF-8?Q?Niklas_S=c3=b6derlund?= <niklas.soderlund@ragnatech.se>,
        Kangjie Lu <kjlu@umn.edu>
Cc:     pakki001@umn.edu, Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190309070527.2657-1-kjlu@umn.edu>
 <20190309110217.GA5281@bigcity.dyn.berto.se>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <c16cbf21-562a-ba00-020e-6232fc27e9f9@xs4all.nl>
Date:   Thu, 28 Mar 2019 16:26:03 +0100
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On 3/9/19 12:02 PM, Niklas Söderlund wrote:
> Hi Kangjie,
> 
> Thanks for your patch.
> 
> On 2019-03-09 01:05:27 -0600, Kangjie Lu wrote:
>> In case of_match_node cannot find a match, the fix returns
>> -EINVAL to avoid NULL pointer dereference.
>>
>> Signed-off-by: Kangjie Lu <kjlu@umn.edu>
>> ---
>>  drivers/media/platform/rcar-vin/rcar-core.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/media/platform/rcar-vin/rcar-core.c b/drivers/media/platform/rcar-vin/rcar-core.c
>> index f0719ce24b97..a058e2023ca8 100644
>> --- a/drivers/media/platform/rcar-vin/rcar-core.c
>> +++ b/drivers/media/platform/rcar-vin/rcar-core.c
>> @@ -266,6 +266,8 @@ static int rvin_group_init(struct rvin_group *group, struct rvin_dev *vin)
>>  
>>  	match = of_match_node(vin->dev->driver->of_match_table,
>>  			      vin->dev->of_node);
>> +	if (unlikely(!match))
>> +		return -EINVAL;
> 
> I don't think this is needed. The driver depends on selects OF and if we 
> get this far we it is because we had a match already. The reason to call 
> of_match_node() here is simply to retrieve which of the possible 
> compatible strings was matched.
> 
> Am I missing something? What scenario do you see where this can fail?

And even if it can fail, then please drop the 'unlikely'.

Regards,

	Hans

> 
>>  
>>  	strscpy(mdev->driver_name, KBUILD_MODNAME, sizeof(mdev->driver_name));
>>  	strscpy(mdev->model, match->compatible, sizeof(mdev->model));
>> -- 
>> 2.17.1
>>
>