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

From: Joseph Qi <joseph.qi@linux.alibaba.com>
To: Yang Yingliang <yangyingliang@huawei.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: mark@fasheh.com, jlbec@evilplan.org, akpm@linux-foundation.org,
	ocfs2-devel <ocfs2-devel@oss.oracle.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ocfs2: possible memory leak in mlog_sys_init()
Date: Thu, 20 Oct 2022 10:06:48 +0800	[thread overview]
Message-ID: <30747fd7-fe79-2ed8-ce63-425a008e3e4f@linux.alibaba.com> (raw)
In-Reply-To: <f6bc6dd3-f7b7-e757-fc36-d1cfbc7305e5@huawei.com>


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?

Thanks,
Joseph

> I think kset_register() is similar with device_register(), if it fails need another put function to give
> up reference in driver.
>