From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Mon, 09 Apr 2012 23:47:17 GMT
Subject: Re: [PATCH] list-objects: perform NULL check before the variable is dereferenced
Message-ID: <CACsJy8ASo8j+hmJ7Kw2uLcD9cS8SXc6yOoc5GDUcFHYk9W9a_g@mail.gmail.com>
In-Reply-To: <7v7gxowxfh.fsf@alter.siamese.dyndns.org>

2012/4/10 Junio C Hamano <gitster@pobox.com>:
> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
>> ---
>>  list-objects.c |   10 ++++++----
>>  1 files changed, 6 insertions(+), 4 deletions(-)
>
> Please explain why this is needed?
>
> I can see that process_blob() is called from process_tree() which passes
> the return value from lookup_blob(entry.sha1) directly without looking at
> it.  lookup_blob() can issue an error message and return NULL if there is
> a SHA-1 collision with an object that is not a blob.

to avoid segmentation fault in that case, if "blob" is NULL, it dies
at blob->object anyway and the check "if (!obj)" is useless.

>
>> diff --git a/list-objects.c b/list-objects.c
>> index 3dd4a96..34044d9 100644
>> --- a/list-objects.c
>> +++ b/list-objects.c
>> @@ -15,12 +15,13 @@ static void process_blob(struct rev_info *revs,
>>                        const char *name,
>>                        void *cb_data)
>>  {
>> -     struct object *obj = &blob->object;
>> +     struct object *obj;
>>
>>       if (!revs->blob_objects)
>>               return;
>> -     if (!obj)
>> +     if (!blob)
>>               die("bad blob object");
>> +     obj = &blob->object;
>>       if (obj->flags & (UNINTERESTING | SEEN))
>>               return;
>>       obj->flags |= SEEN;
>> @@ -67,7 +68,7 @@ static void process_tree(struct rev_info *revs,
>>                        const char *name,
>>                        void *cb_data)
>>  {
>> -     struct object *obj = &tree->object;
>> +     struct object *obj;
>>       struct tree_desc desc;
>>       struct name_entry entry;
>>       struct name_path me;
>> @@ -77,8 +78,9 @@ static void process_tree(struct rev_info *revs,
>>
>>       if (!revs->tree_objects)
>>               return;
>> -     if (!obj)
>> +     if (!tree)
>>               die("bad tree object");
>> +     obj = &tree->object;
>>       if (obj->flags & (UNINTERESTING | SEEN))
>>               return;
>>       if (parse_tree(tree) < 0)



-- 
Duy