linux-kernel - Re: [PATCH 00/11] fix memory leak while kset

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Date:   Fri, 21 Oct 2022 07:37:48 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luben Tuikov <luben.tuikov@....com>
Cc:     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,
        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 00/11] fix memory leak while kset_register() fails

On Fri, Oct 21, 2022 at 01:29:31AM -0400, Luben Tuikov wrote:
> 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.

Based on this, can kset_register() just clean up from itself when an
error happens?  Ideally that would be the case, as the odds of a kset
being embedded in a larger structure is probably slim, but we would have
to search the tree to make sure.

thanks,

greg k-h