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

[Gao Xiang]

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().

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