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Message-ID: <c7a3bdac-3ed6-e695-5c45-e7007615a4d9@linux.alibaba.com>
Date:   Tue, 18 Oct 2022 21:39:36 +0800
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Subject: Re: [PATCH] ocfs2: possible memory leak in mlog_sys_init()
Content-Language: en-US
To:     Yang Yingliang <yangyingliang@huawei.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>
From:   Joseph Qi <joseph.qi@linux.alibaba.com>
In-Reply-To: <09bb2844-e20a-98e8-c2af-5b6c4795d48e@huawei.com>
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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...

Thanks,
Joseph