linux-kernel - Re: [PATCH v2] kset: fix memory leak when kset

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Date:   Mon, 24 Oct 2022 22:53:51 -0400
From:   Luben Tuikov <luben.tuikov@....com>
To:     Yang Yingliang <yangyingliang@...wei.com>,
        linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-erofs@...ts.ozlabs.org, ocfs2-devel@....oracle.com,
        linux-mtd@...ts.infradead.org, amd-gfx@...ts.freedesktop.org
Cc:     gregkh@...uxfoundation.org, rafael@...nel.org, somlo@....edu,
        mst@...hat.com, jaegeuk@...nel.org, chao@...nel.org,
        hsiangkao@...ux.alibaba.com, huangjianan@...o.com, mark@...heh.com,
        jlbec@...lplan.org, joseph.qi@...ux.alibaba.com,
        akpm@...ux-foundation.org, alexander.deucher@....com,
        richard@....at, liushixin2@...wei.com
Subject: Re: [PATCH v2] kset: fix memory leak when kset_register() returns
 error

On 2022-10-24 08:19, Yang Yingliang wrote:
> Inject fault while loading module, kset_register() may fail.
> If it fails, the name allocated by kobject_set_name() which
> is called before kset_register() is leaked, because refcount
> of kobject is hold in kset_init().
> 
> As a kset may be embedded in a larger structure which needs
> be freed in release() function or error path in callers, we
> can not call kset_put() in kset_register(), or it will cause
> double free, so just call kfree_const() to free the name and
> set it to NULL.
> 
> With this fix, the callers don't need to care about the name
> freeing and call an extra kset_put() if kset_register() fails.
> 
> Suggested-by: Luben Tuikov <luben.tuikov@....com>
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
> v1 -> v2:
>   Free name inside of kset_register() instead of calling kset_put()
>   in drivers.
> ---
>  lib/kobject.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/kobject.c b/lib/kobject.c
> index a0b2dbfcfa23..3409a89c81e5 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
>  /**
>   * kset_register() - Initialize and add a kset.
>   * @k: kset.
> + *
> + * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
> + * which is called before kset_register() in caller need be freed.
>   */

The "need be freed" is confusing here because it is not clear if the user
needs to do this or if it is done by the code. Since it is the latter,
it should read "_is_ freed". Like this (no "NOTE"):

"On error, the kset.kobj.name allocated by kobj_set_name(),
 which must be called before kset_register() is called, is freed
 by this function."

Regards,
Luben

>  int kset_register(struct kset *k)
>  {
> @@ -844,8 +847,11 @@ int kset_register(struct kset *k)
>  
>  	kset_init(k);
>  	err = kobject_add_internal(&k->kobj);
> -	if (err)
> +	if (err) {
> +		kfree_const(k->kobj.name);
> +		k->kobj.name = NULL;
>  		return err;
> +	}
>  	kobject_uevent(&k->kobj, KOBJ_ADD);
>  	return 0;
>  }