linux-kernel - Re: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor

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Date:   Thu, 07 Dec 2017 17:56:00 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in
 governor_store

Hi Chanwoo,

Quoting Chanwoo Choi <cw00.choi@...sung.com>:

> On 2017년 12월 07일 05:20, Gustavo A. R. Silva wrote:
>> df->governor is being dereferenced before it is null checked,
>> hence there is a potential null pointer dereference.
>>
>> Notice that df->governor is being null checked at line 1004:
>> if (df->governor) {, which implies it might be null.
>>
>> Fix this by null checking df->governor before dereferencing it.
>>
>> Addresses-Coverity-ID: 1401988 ("Dereference before null check")
>> Fixes: bcf23c79c4e4 ("PM / devfreq: Fix available_governor sysfs")
>> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
>> ---
>>  drivers/devfreq/devfreq.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 78fb496..14fe76b 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -996,7 +996,8 @@ static ssize_t governor_store(struct device  
>> *dev, struct device_attribute *attr,
>>  	if (df->governor == governor) {
>>  		ret = 0;
>>  		goto out;
>> -	} else if (df->governor->immutable || governor->immutable) {
>> +	} else if ((df->governor && df->governor->immutable) ||
>> +					governor->immutable) {
>>  		ret = -EINVAL;
>>  		goto out;
>>  	}
>>
>
> Actually, df->governor would be never NULL because devfreq_add_device()
> initializes the ->governor always. But, governor_store() doesn't know it.
>

I got it.

> So, looks good to me.
> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
>

Thank you

--
Gustavo A. R. Silva