Ocfs2 devel - Aug 2019 - [PATCH 3/3] fs: ocfs2: Fix a possible null-pointer dereference in ocfs2_info_scan_inode_alloc()

Hi Jia-Ju and Joseph,


Busy with a training session last week, so late for reviewing this patch.

I think this patch might not be necessary and a little violates original 
logic.

Please check out my comments inline.


On 2019/7/26 5:39 ??, Joseph Qi wrote:
>
> On 19/7/26 11:37, Jia-Ju Bai wrote:
>> In ocfs2_info_scan_inode_alloc(), there is an if statement on line 283
>> to check whether inode_alloc is NULL:
>>      if (inode_alloc)
>>
>> When inode_alloc is NULL, it is used on line 287:
>>      ocfs2_inode_lock(inode_alloc, &bh, 0);
>>          ocfs2_inode_lock_full_nested(inode, ...)
>>              struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>
>> Thus, a possible null-pointer dereference may occur.
>>
>> To fix this bug, inode_alloc is checked on line 286.
>>
>> This bug is found by a static analysis tool STCheck written by us.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990 at gmail.com>
> Looks good.
> Reviewed-by: Joseph Qi <joseph.qi at linux.alibaba.com>
>> ---
>>   fs/ocfs2/ioctl.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
>> index d6f7b299eb23..efeea208fdeb 100644
>> --- a/fs/ocfs2/ioctl.c
>> +++ b/fs/ocfs2/ioctl.c
>> @@ -283,7 +283,7 @@ static int ocfs2_info_scan_inode_alloc(struct
ocfs2_super *osb,
>>   	if (inode_alloc)
>>   		inode_lock(inode_alloc);
>>   
>> -	if (o2info_coherent(&fi->ifi_req)) {
>> +	if (inode_alloc && o2info_coherent(&fi->ifi_req)) {

If caller is asking for strict coherency but *inode_alloc* is NULL, we 
fallback to non-coherency branch?

I think this is destroying the file semantics. Returning error to caller 
is better?


On the other hand, from the code path:

ocfs2_info_handle_freeinode()

 ??? if o2info_coherent() then inode_alloc = 
ocfs2_get_system_file_inode() ---> here we can ensure that being passed 
*inode_alloc* can't be NULL

 ??? ocfs2_info_scan_inode_alloc()


Thanks,

Changwei

>>   		status = ocfs2_inode_lock(inode_alloc, &bh, 0);
>>   		if (status < 0) {
>>   			mlog_errno(status);
>>
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On 19/8/5 10:17, Changwei Ge wrote:
> Hi Jia-Ju and Joseph,
> 
> 
> Busy with a training session last week, so late for reviewing this patch.
> 
> I think this patch might not be necessary and a little violates original
logic.
> 
> Please check out my comments inline.
> 
> 
> On 2019/7/26 5:39 ??, Joseph Qi wrote:
>>
>> On 19/7/26 11:37, Jia-Ju Bai wrote:
>>> In ocfs2_info_scan_inode_alloc(), there is an if statement on line
283
>>> to check whether inode_alloc is NULL:
>>> ???? if (inode_alloc)
>>>
>>> When inode_alloc is NULL, it is used on line 287:
>>> ???? ocfs2_inode_lock(inode_alloc, &bh, 0);
>>> ???????? ocfs2_inode_lock_full_nested(inode, ...)
>>> ???????????? struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>
>>> Thus, a possible null-pointer dereference may occur.
>>>
>>> To fix this bug, inode_alloc is checked on line 286.
>>>
>>> This bug is found by a static analysis tool STCheck written by us.
>>>
>>> Signed-off-by: Jia-Ju Bai <baijiaju1990 at gmail.com>
>> Looks good.
>> Reviewed-by: Joseph Qi <joseph.qi at linux.alibaba.com>
>>> ---
>>> ? fs/ocfs2/ioctl.c | 2 +-
>>> ? 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
>>> index d6f7b299eb23..efeea208fdeb 100644
>>> --- a/fs/ocfs2/ioctl.c
>>> +++ b/fs/ocfs2/ioctl.c
>>> @@ -283,7 +283,7 @@ static int ocfs2_info_scan_inode_alloc(struct
ocfs2_super *osb,
>>> ????? if (inode_alloc)
>>> ????????? inode_lock(inode_alloc);
>>> ? -??? if (o2info_coherent(&fi->ifi_req)) {
>>> +??? if (inode_alloc &&
o2info_coherent(&fi->ifi_req)) {
> 
> 
> If caller is asking for strict coherency but *inode_alloc* is NULL, we
fallback to non-coherency branch?
> 
> I think this is destroying the file semantics. Returning error to caller is
better?
> 
> 
> On the other hand, from the code path:
> 
> ocfs2_info_handle_freeinode()
> 
> ??? if o2info_coherent() then inode_alloc = ocfs2_get_system_file_inode()
---> here we can ensure that being passed *inode_alloc* can't be NULL
> 
> ??? ocfs2_info_scan_inode_alloc()
> 
You are right, the caller make sure inode_alloc won't be NULL if
o2info_coherent().
So adding this check just make it more explicitly, right?
I don't get how it breaks the original logic.

Thanks,
Joseph