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

[Gao Xiang]

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.

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