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Date:   Fri, 21 Oct 2022 01:29:31 -0400
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Subject: Re: [PATCH 00/11] fix memory leak while kset_register() fails
Content-Language: en-CA
To:     Yang Yingliang <yangyingliang@huawei.com>,
        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
Cc:     gregkh@linuxfoundation.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,
        richard@nod.at, liushixin2@huawei.com
References: <20221021022102.2231464-1-yangyingliang@huawei.com>
From:   Luben Tuikov <luben.tuikov@amd.com>
In-Reply-To: <20221021022102.2231464-1-yangyingliang@huawei.com>
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On 2022-10-20 22:20, Yang Yingliang wrote:
> The previous discussion link:
> https://lore.kernel.org/lkml/0db486eb-6927-927e-3629-958f8f211194@huawei.com/T/

The very first discussion on this was here:

https://www.spinics.net/lists/dri-devel/msg368077.html

Please use this link, and not the that one up there you which quoted above,
and whose commit description is taken verbatim from the this link.

> 
> kset_register() is currently used in some places without calling
> kset_put() in error path, because the callers think it should be
> kset internal thing to do, but the driver core can not know what
> caller doing with that memory at times. The memory could be freed
> both in kset_put() and error path of caller, if it is called in
> kset_register().

As I explained in the link above, the reason there's
a memory leak is that one cannot call kset_register() without
the kset->kobj.name being set--kobj_add_internal() returns -EINVAL,
in this case, i.e. kset_register() fails with -EINVAL.

Thus, the most common usage is something like this:

	kobj_set_name(&kset->kobj, format, ...);
	kset->kobj.kset = parent_kset;
	kset->kobj.ktype = ktype;
	res = kset_register(kset);

So, what is being leaked, is the memory allocated in kobj_set_name(),
by the common idiom shown above. This needs to be mentioned in
the documentation, at least, in case, in the future this is absolved
in kset_register() redesign, etc.

Regards,
Luben

> 
> So make the function documentation more explicit about calling
> kset_put() in the error path of caller first, so that people
> have a chance to know what to do here, then fixes this leaks
> by calling kset_put() from callers.
> 
> Liu Shixin (1):
>   ubifs: Fix memory leak in ubifs_sysfs_init()
> 
> Yang Yingliang (10):
>   kset: fix documentation for kset_register()
>   kset: add null pointer check in kset_put()
>   bus: fix possible memory leak in bus_register()
>   kobject: fix possible memory leak in kset_create_and_add()
>   class: fix possible memory leak in __class_register()
>   firmware: qemu_fw_cfg: fix possible memory leak in
>     fw_cfg_build_symlink()
>   f2fs: fix possible memory leak in f2fs_init_sysfs()
>   erofs: fix possible memory leak in erofs_init_sysfs()
>   ocfs2: possible memory leak in mlog_sys_init()
>   drm/amdgpu/discovery: fix possible memory leak
> 
>  drivers/base/bus.c                            | 4 +++-
>  drivers/base/class.c                          | 6 ++++++
>  drivers/firmware/qemu_fw_cfg.c                | 2 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 5 +++--
>  fs/erofs/sysfs.c                              | 4 +++-
>  fs/f2fs/sysfs.c                               | 4 +++-
>  fs/ocfs2/cluster/masklog.c                    | 7 ++++++-
>  fs/ubifs/sysfs.c                              | 2 ++
>  include/linux/kobject.h                       | 3 ++-
>  lib/kobject.c                                 | 5 ++++-
>  10 files changed, 33 insertions(+), 9 deletions(-)
>