2017-12-06 20:20:23

by Gustavo A. R. Silva

Subject: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor_store

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 <[email protected]>
---
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;
}
--
2.7.4

2017-12-07 01:24:26

by Chanwoo Choi

Subject: Re: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor_store

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 <[email protected]>
> ---
> 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.

So, looks good to me.
Reviewed-by: Chanwoo Choi <[email protected]>

--
Best Regards,
Chanwoo Choi
Samsung Electronics

2017-12-07 02:42:07

by MyungJoo Ham

Subject: RE: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor_store

> 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 <[email protected]>

Acked-by: MyungJoo Ham <[email protected]>


Cheers,
MyungJoo

> ---
> 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

2017-12-07 23:56:03

by Gustavo A. R. Silva

Subject: Re: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor_store

Hi Chanwoo,

Quoting Chanwoo Choi <[email protected]>:

> 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 <[email protected]>
>> ---
>> 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 <[email protected]>
>

Thank you

--
Gustavo A. R. Silva

2017-12-07 23:57:46

by Gustavo A. R. Silva

Subject: Re: [PATCH] PM / devfreq: Fix potential NULL pointer dereference in governor_store

Quoting MyungJoo Ham <[email protected]>:

>> 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 <[email protected]>
>
> Acked-by: MyungJoo Ham <[email protected]>
>

Thank you, MyungJoo

--
Gustavo A. R. Silva