Re: [Qemu-devel] [Virtio-fs] [PATCH 2/5] virtiofsd: prevent lo_lookup() NULL pointer dereference

[piaojun]

On 2019/7/29 23:41, Stefan Hajnoczi wrote:
> On Mon, Jul 29, 2019 at 08:35:36PM +0800, piaojun wrote:
>> Hi Stefan,
>>
>> On 2019/7/26 17:11, Stefan Hajnoczi wrote:
>>> Most lo_do_lookup() have already checked that the parent inode exists.
>>> lo_lookup() hasn't and can therefore hit a NULL pointer dereference when
>>> lo_inode(req, parent) returns NULL.
>>>
>>> Signed-off-by: Stefan Hajnoczi <address@hidden>
>>> ---
>>>  contrib/virtiofsd/passthrough_ll.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/contrib/virtiofsd/passthrough_ll.c 
>>> b/contrib/virtiofsd/passthrough_ll.c
>>> index 9ae1381618..277a17fc03 100644
>>> --- a/contrib/virtiofsd/passthrough_ll.c
>>> +++ b/contrib/virtiofsd/passthrough_ll.c
>>> @@ -766,6 +766,10 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t 
>>> parent, const char *name,
>>>     struct lo_data *lo = lo_data(req);
>>>     struct lo_inode *inode, *dir = lo_inode(req, parent);
>>>  
>>> +   if (!dir) {
>>> +           return EBADF;
>>> +   }
>>> +
>>
>> I worry about that dir will be released or set NULL just after NULL
>> checking. Or could we use some lock to prevent the simultaneity?
> 
> Yes, I agree.  I haven't audited lo_inode yet, but it needs a refcount
> and/or lock to ensure accesses are safe.  I'll do that and other things
> in a separate patch series.
> 
> Stefan

OK, that sounds good.

Jun

>