Re: [PATCH v2] kset: fix memory leak when kset_register() returns error

From: Greg KH <gregkh@linuxfoundation.org>
To: Yang Yingliang <yangyingliang@huawei.com>
Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-erofs@lists.ozlabs.org, ocfs2-devel@oss.oracle.com,
	linux-mtd@lists.infradead.org, amd-gfx@lists.freedesktop.org,
	rafael@kernel.org, somlo@cmu.edu, mst@redhat.com,
	jaegeuk@kernel.org, chao@kernel.org, hsiangkao@linux.alibaba.com,
	huangjianan@oppo.com, mark@fasheh.com, jlbec@evilplan.org,
	joseph.qi@linux.alibaba.com, akpm@linux-foundation.org,
	alexander.deucher@amd.com, luben.tuikov@amd.com, richard@nod.at,
	liushixin2@huawei.com
Subject: Re: [PATCH v2] kset: fix memory leak when kset_register() returns error
Date: Mon, 24 Oct 2022 15:52:56 +0200	[thread overview]
Message-ID: <Y1aYuLmlXBRvMP1Z@kroah.com> (raw)
In-Reply-To: <20221024121910.1169801-1-yangyingliang@huawei.com>

On Mon, Oct 24, 2022 at 08:19:10PM +0800, 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@amd.com>
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.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.

This comment doesn't make any sense anymore.  No caller needs to worry
about this, right?

>   */
>  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;

Why are you setting the name here to NULL?

thanks,

greg k-h

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