Re: [PATCH] ocfs2: possible memory leak in mlog_sys_init()

[Yang Yingliang <yangyingliang@huawei.com>]

On 2022/10/20 18:18, Greg Kroah-Hartman wrote:
> On Thu, Oct 20, 2022 at 10:06:48AM +0800, Joseph Qi wrote:
>>
>> On 10/19/22 10:57 AM, Yang Yingliang wrote:
>>> On 2022/10/19 10:26, Joseph Qi wrote:
>>>> On 10/18/22 10:28 PM, Yang Yingliang wrote:
>>>>> On 2022/10/18 21:39, Joseph Qi wrote:
>>>>>> On 10/18/22 6:33 PM, Yang Yingliang wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 2022/10/18 17:02, Joseph Qi wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> On 10/18/22 3:52 PM, Yang Yingliang wrote:
>>>>>>>>> Inject fault while probing module, kset_register() may fail,
>>>>>>>>> if it fails, but the refcount of kobject is not decreased to
>>>>>>>>> 0, the name allocated in kobject_set_name() is leaked. Fix
>>>>>>>>> this by calling kset_put(), so that name can be freed in
>>>>>>>>> callback function kobject_cleanup().
>>>>>>>>>
>>>>>>>>> unreferenced object 0xffff888100da9348 (size 8):
>>>>>>>>>       comm "modprobe", pid 257, jiffies 4294701096 (age 33.334s)
>>>>>>>>>       hex dump (first 8 bytes):
>>>>>>>>>         6c 6f 67 6d 61 73 6b 00                          logmask.
>>>>>>>>>       backtrace:
>>>>>>>>>         [<00000000306e441c>] __kmalloc_node_track_caller+0x44/0x1b0
>>>>>>>>>         [<000000007c491a9e>] kstrdup+0x3a/0x70
>>>>>>>>>         [<0000000015719a3b>] kstrdup_const+0x63/0x80
>>>>>>>>>         [<0000000084e458ea>] kvasprintf_const+0x149/0x180
>>>>>>>>>         [<0000000091302b42>] kobject_set_name_vargs+0x56/0x150
>>>>>>>>>         [<000000005f48eeac>] kobject_set_name+0xab/0xe0
>>>>>>>>>
>>>>>>>>> Fixes: 34980ca8faeb ("Drivers: clean up direct setting of the name of a kset")
>>>>>>>>> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
>>>>>>>>> ---
>>>>>>>>>      fs/ocfs2/cluster/masklog.c | 7 ++++++-
>>>>>>>>>      1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/fs/ocfs2/cluster/masklog.c b/fs/ocfs2/cluster/masklog.c
>>>>>>>>> index 563881ddbf00..7f9ba816d955 100644
>>>>>>>>> --- a/fs/ocfs2/cluster/masklog.c
>>>>>>>>> +++ b/fs/ocfs2/cluster/masklog.c
>>>>>>>>> @@ -156,6 +156,7 @@ static struct kset mlog_kset = {
>>>>>>>>>      int mlog_sys_init(struct kset *o2cb_kset)
>>>>>>>>>      {
>>>>>>>>>          int i = 0;
>>>>>>>>> +    int ret;
>>>>>>>>>            while (mlog_attrs[i].attr.mode) {
>>>>>>>>>              mlog_default_attrs[i] = &mlog_attrs[i].attr;
>>>>>>>>> @@ -165,7 +166,11 @@ int mlog_sys_init(struct kset *o2cb_kset)
>>>>>>>>>            kobject_set_name(&mlog_kset.kobj, "logmask");
>>>>>>>>>          mlog_kset.kobj.kset = o2cb_kset;
>>>>>>>>> -    return kset_register(&mlog_kset);
>>>>>>>>> +    ret = kset_register(&mlog_kset);
>>>>>>>> If register fails, it will call unregister in o2cb_sys_init(), which
>>>>>>>> will put kobject.
>>>>>>> They are different ksets, the kset unregistered in o2cb_sys_init() is 'o2cb_kset', the
>>>>>>> kset used to registered in mlog_sys_init() is 'mlog_kset', and they hold difference
>>>>>>> refcounts.
>>>>>>> Yes, you are right. I've mixed the two ksets up.
>>>>>> In theory, kset_register() may return error because of a NULL kset, so
>>>>>> here we may not call kset_put() directly, I'm not sure if a static
>>>>>> checker will happy.
>>>>>> Though this can't happen since it's already statically allocated...
>>>>> kset_register() may fail if kobject_add_internal() return error (can't allocate memory), the name
>>>>> "logmask" is dynamically alloctated while ocfs2 is compile as module and insert it (if ocfs2 is
>>>>> built in kernel, the name is constant, it won't cause a leak), so the name can be leaked.
>>>> What I mean is kset_register() may fail with many reasons, or even
>>>> without kset_init().
>>>> I wonder if we have to handle this internal kset_register(), but not
>>>> leave it to caller. This may benefit other callers as well.
>>>>
>>>> Something like:
>>>> err = kobject_add_internal(&k->kobj);
>>>> if (err) {
>>>>      kset_put(k);
>>>>      return err;
>>>> }
>>> I had think about this method to fix this, but some kset is allocated dynamically in driver and
>>> it's freed in callback function which is called after kset_put() and in error path in driver will free
>>> it again, it leads double free in some drivers.
>>>
>> I don't think it's good idea that caller has to take care part of the
>> internal logic of kset_register() in case of error.
>> Hi Greg, what do you think?
> I think if you are messing around with raw ksets, you have to handle
> them properly :)
>
> For some driver and kobject core functions, once you call register, you
> have to call put() to handle an error because the driver core can not
> know what you are doing with that memory at times.
>
> But, maybe for ksets this is not needed and the kobject core can
> properly clean up from an error here.  Yang, can you please look into
> this?  That might make this much simpler.
OK, I will look into this to see how to make it simpler for drivers.
>
> Either way, the documentation for kset_register() needs to be fixed up
> first, so that people have a chance to know what to do here and THEN we
> can fix up the callers like this.
>
> Yang, can you do this all as one long series that I can take through the
> driver core tree.  No need to scatter it all across a bunch of different
> subsystems.
OK, I will fix all these in one series.

Thanks,
Yang
>
> thanks,
>
> greg k-h
> .