[PATCH] fbdev: fix possible NULL pointer derefernce

[PATCH] fbdev: fix possible NULL pointer derefernce

[Daeseok Youn]

The spec->modedb can be NULL by fb_create_modedb().

And also smatch says:
drivers/video/fbdev/core/fbmon.c:975 fb_edid_to_monspecs() error:
potential null dereference 'specs->modedb'.
(fb_create_modedb returns null)

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
---
 drivers/video/fbdev/core/fbmon.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index c204ebe..db274ca 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -966,6 +966,9 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)
 
 	specs->modedb = fb_create_modedb(edid, &specs->modedb_len);
 
+	if (!specs->modedb)
+		return;
+
 	/*
 	 * Workaround for buggy EDIDs that sets that the first
 	 * detailed timing is preferred but has not detailed
-- 
1.7.4.4

Re: [PATCH] fbdev: fix possible NULL pointer derefernce

[Jean-Christophe PLAGNIOL-VILLARD]

On Apr 16, 2014, at 5:40 PM, Daeseok Youn <daeseok.youn@gmail.com> wrote:

> 
> The spec->modedb can be NULL by fb_create_modedb().
> 
> And also smatch says:
> drivers/video/fbdev/core/fbmon.c:975 fb_edid_to_monspecs() error:
> potential null dereference 'specs->modedb'.
> (fb_create_modedb returns null)
> 
> Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
> ---
> drivers/video/fbdev/core/fbmon.c |    3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
> index c204ebe..db274ca 100644
> --- a/drivers/video/fbdev/core/fbmon.c
> +++ b/drivers/video/fbdev/core/fbmon.c
> @@ -966,6 +966,9 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)
> 
> 	specs->modedb = fb_create_modedb(edid, &specs->modedb_len);
> 
> +	if (!specs->modedb)
> +		return;
> +

we need to return an error and trace it

Best Regards,
J.
> 	/*
> 	 * Workaround for buggy EDIDs that sets that the first
> 	 * detailed timing is preferred but has not detailed
> -- 
> 1.7.4.4
> 

Re: [PATCH] fbdev: fix possible NULL pointer derefernce

[DaeSeok Youn]

Hello,

2014-04-16 21:38 GMT+09:00 Jean-Christophe PLAGNIOL-VILLARD
<plagnioj@jcrosoft.com>:
>
> On Apr 16, 2014, at 5:40 PM, Daeseok Youn <daeseok.youn@gmail.com> wrote:
>
>>
>> The spec->modedb can be NULL by fb_create_modedb().
>>
>> And also smatch says:
>> drivers/video/fbdev/core/fbmon.c:975 fb_edid_to_monspecs() error:
>> potential null dereference 'specs->modedb'.
>> (fb_create_modedb returns null)
>>
>> Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
>> ---
>> drivers/video/fbdev/core/fbmon.c |    3 +++
>> 1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
>> index c204ebe..db274ca 100644
>> --- a/drivers/video/fbdev/core/fbmon.c
>> +++ b/drivers/video/fbdev/core/fbmon.c
>> @@ -966,6 +966,9 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)
>>
>>       specs->modedb = fb_create_modedb(edid, &specs->modedb_len);
>>
>> +     if (!specs->modedb)
>> +             return;
>> +
>
> we need to return an error and trace it
Yes, you're right. I will change return type from void to int and add
to handle an error when this function(fb_edid_to_monspecs) is called.

I will send this patch as your comment.

Thanks for review.

Daeseok Youn.
>
> Best Regards,
> J.
>>       /*
>>        * Workaround for buggy EDIDs that sets that the first
>>        * detailed timing is preferred but has not detailed
>> --
>> 1.7.4.4
>>
>

Re: [PATCH] fbdev: fix possible NULL pointer derefernce

[DaeSeok Youn]

Hello,

2014-04-17 9:00 GMT+09:00 DaeSeok Youn <daeseok.youn@gmail.com>:
> Hello,
>
> 2014-04-16 21:38 GMT+09:00 Jean-Christophe PLAGNIOL-VILLARD
> <plagnioj@jcrosoft.com>:
>>
>> On Apr 16, 2014, at 5:40 PM, Daeseok Youn <daeseok.youn@gmail.com> wrote:
>>
>>>
>>> The spec->modedb can be NULL by fb_create_modedb().
>>>
>>> And also smatch says:
>>> drivers/video/fbdev/core/fbmon.c:975 fb_edid_to_monspecs() error:
>>> potential null dereference 'specs->modedb'.
>>> (fb_create_modedb returns null)
>>>
>>> Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
>>> ---
>>> drivers/video/fbdev/core/fbmon.c |    3 +++
>>> 1 files changed, 3 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
>>> index c204ebe..db274ca 100644
>>> --- a/drivers/video/fbdev/core/fbmon.c
>>> +++ b/drivers/video/fbdev/core/fbmon.c
>>> @@ -966,6 +966,9 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)
>>>
>>>       specs->modedb = fb_create_modedb(edid, &specs->modedb_len);
>>>
>>> +     if (!specs->modedb)
>>> +             return;
>>> +
>>
>> we need to return an error and trace it
> Yes, you're right. I will change return type from void to int and add
> to handle an error when this function(fb_edid_to_monspecs) is called.
>
I try to look at the fbdev code related with fb_edid_to_monspecs().
And the result, I think it doesn't need to return an error and trace it.
My patch is also useless because modedb_len is zero when
fb_create_modedb() returns NULL so It cannot be dereferenced.

And callers of this function seem to need a log but I think they don't need to
handling an error. Some functions are handling error with checking
NULL of modedb variable,
they are just printing an error message.

If I am wrong or you have reasons for handling an error on that
function, please let me know.

Regards,
Daeseok Youn.

> I will send this patch as your comment.
>
> Thanks for review.
>
> Daeseok Youn.
>>
>> Best Regards,
>> J.
>>>       /*
>>>        * Workaround for buggy EDIDs that sets that the first
>>>        * detailed timing is preferred but has not detailed
>>> --
>>> 1.7.4.4
>>>
>>