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

[Chao Yu]

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?

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