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Subject: Re: [PATCH] ocfs2: possible memory leak in mlog_sys_init()
To:     Joseph Qi <joseph.qi@linux.alibaba.com>,
        <linux-kernel@vger.kernel.org>, <ocfs2-devel@oss.oracle.com>
CC:     <mark@fasheh.com>, <jlbec@evilplan.org>,
        <gregkh@linuxfoundation.org>, <akpm@linux-foundation.org>
References: <20221018075213.736562-1-yangyingliang@huawei.com>
 <bf27f347-5ced-98e5-f188-659cc2a9736f@linux.alibaba.com>
 <09bb2844-e20a-98e8-c2af-5b6c4795d48e@huawei.com>
 <c7a3bdac-3ed6-e695-5c45-e7007615a4d9@linux.alibaba.com>
 <0db486eb-6927-927e-3629-958f8f211194@huawei.com>
 <1adbbf98-2700-27c8-4aca-9510bca91458@linux.alibaba.com>
From:   Yang Yingliang <yangyingliang@huawei.com>
Message-ID: <f6bc6dd3-f7b7-e757-fc36-d1cfbc7305e5@huawei.com>
Date:   Wed, 19 Oct 2022 10:57:49 +0800
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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 think kset_register() is similar with device_register(), if it fails 
need another put function to give
up reference in driver.

Thanks,
Yang
>
> Thanks,
> Joseph
>
> .