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

[Joseph Qi <joseph.qi@linux.alibaba.com>]

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@gmail.com>
>> Looks good.
>> Reviewed-by: Joseph Qi <joseph.qi@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