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

From: Joseph Qi <joseph.qi@linux.alibaba.com>
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
Subject: Re: [PATCH] ocfs2: possible memory leak in mlog_sys_init()
Date: Wed, 19 Oct 2022 10:26:15 +0800	[thread overview]
Message-ID: <1adbbf98-2700-27c8-4aca-9510bca91458@linux.alibaba.com> (raw)
In-Reply-To: <0db486eb-6927-927e-3629-958f8f211194@huawei.com>

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;
}

Thanks,
Joseph