[PATCH] erofs: fix possible memory leak in erofs_init_sysfs()

[Chao Yu]

On 2022/10/20 17:14, Gao Xiang wrote:
> Hi Chao,
> 
> On Thu, Oct 20, 2022 at 04:49:34PM +0800, Chao Yu wrote:
>> On 2022/10/19 10:21, Gao Xiang wrote:
>>> Hi Yingliang,
>>>
>>> On Tue, Oct 18, 2022 at 03:39:47PM +0800, 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 0xffff888101d228c0 (size 8):
>>>>     comm "modprobe", pid 276, jiffies 4294722700 (age 13.151s)
>>>>     hex dump (first 8 bytes):
>>>>       65 72 6f 66 73 00 ff ff                          erofs...
>>>>     backtrace:
>>>>       [<00000000e2a9a4a6>] __kmalloc_node_track_caller+0x44/0x1b0
>>>>       [<00000000b8ce02de>] kstrdup+0x3a/0x70
>>>>       [<000000004a0e01d2>] kstrdup_const+0x63/0x80
>>>>       [<00000000051b6cda>] kvasprintf_const+0x149/0x180
>>>>       [<000000004dc51dad>] kobject_set_name_vargs+0x56/0x150
>>>>       [<00000000b30f0bad>] kobject_set_name+0xab/0xe0
>>>>
>>>> Fixes: 168e9a76200c ("erofs: add sysfs interface")
>>>> Signed-off-by: Yang Yingliang <yangyingliang at huawei.com>
>>>
>>> Thanks for the catch, the issue itself seems true.  However, I found
>>> several fses all have this issue.
>>>
>>> After I did some discussion with Joseph Qi offline, I'd like to wait
>>> for the conclusion of the following thread:
>>> https://lore.kernel.org/r/bf27f347-5ced-98e5-f188-659cc2a9736f@linux.alibaba.com
>>>
>>> Since I tend to think kset_put() should be one fail step of
>>> kset_register().
>>
>> I guess in error path, it missed to free kobj->name which was allocated by
>> kobject_set_name(&erofs_root.kobj, "erofs"), so calling kset_put() here looks
>> fine?
> 
> We looked into this yesterday.  I think the main problem is that the
> kset_put() a reference which is set in kset_init() of kset_register().
> 
> Therefore such refernece belongs to an internal implementation and
> should not be treated for each kset_register() caller.
> 
> Please correct me if I'm wrong here.

Xiang,

Oh, right, I missed reference count operation in kset_put().

Thanks,

> 
> Thanks,
> Gao Xiang
> 
>>
>> Thanks,
>>
>>>
>>> Thanks,
>>> Gao Xiang
>>>
>>>> ---
>>>>    fs/erofs/sysfs.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
>>>> index 783bb7b21b51..653b35001bc5 100644
>>>> --- a/fs/erofs/sysfs.c
>>>> +++ b/fs/erofs/sysfs.c
>>>> @@ -254,8 +254,10 @@ int __init erofs_init_sysfs(void)
>>>>    	kobject_set_name(&erofs_root.kobj, "erofs");
>>>>    	erofs_root.kobj.parent = fs_kobj;
>>>>    	ret = kset_register(&erofs_root);
>>>> -	if (ret)
>>>> +	if (ret) {
>>>> +		kset_put(&erofs_root);
>>>>    		goto root_err;
>>>> +	}
>>>>    	ret = kobject_init_and_add(&erofs_feat, &erofs_feat_ktype,
>>>>    				   NULL, "features");
>>>> -- 
>>>> 2.25.1