Re: [Qemu-devel] [PATCH] json-parser: Fix potential NULL pointer segfault

[Stefan Weil <sw@weilnetz.de>]

Am 03.09.2012 18:53, schrieb Stefan Weil:
> Am 03.09.2012 18:41, schrieb Luiz Capitulino:
>> On Sat,  1 Sep 2012 12:52:58 +0200
>> Stefan Weil <sw@weilnetz.de> wrote:
>>
>>> Report from smatch:
>>> json-parser.c:474 parse_object(62) error: potential null derefence 
>>> 'dict'.
>>> json-parser.c:553 parse_array(75) error: potential null derefence 
>>> 'list'.
>>>
>>> Label out can be called with list == NULL.
>>>
>>> Signed-off-by: Stefan Weil <sw@weilnetz.de>
>>> ---
>>>   json-parser.c |    8 ++++++--
>>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/json-parser.c b/json-parser.c
>>> index 457291b..c31c759 100644
>>> --- a/json-parser.c
>>> +++ b/json-parser.c
>>> @@ -471,7 +471,9 @@ static QObject *parse_object(JSONParserContext 
>>> *ctxt, va_list *ap)
>>>     out:
>>>       parser_context_restore(ctxt, saved_ctxt);
>>> -    QDECREF(dict);
>>> +    if (dict) {
>>> +        QDECREF(dict);
>>> +    }
>>
>> I prefer changing QDECREF() to a nop if obj is NULL.
>
> That's fine for me, too. If everybody agrees, I'll send two new
> patches: one to change QDECREF, one to remove the if statements
> from other code locations which use the same pattern as
> my original patch.
>
> Cheers,
>
> - sw
>
>

What about modifying QOBJECT to return NULL if called with a NULL pointer?
That would be a more generic fix for the same problem.

In either case, the code will be a little larger and slower,
but that should not matter because it is not time critical.

Regards,

Stefan W.