Re: [PATCH 00/11] fix memory leak while kset_register() fails

[Yang Yingliang]

On 2022/10/21 13:37, Greg KH wrote:
> 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@xxxxxxxxxx/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.
I have search the whole tree, the kset used in bus_register() - patch 
#3, kset_create_and_add() - patch #4
__class_register() - patch #5,  fw_cfg_build_symlink() - patch #6 and 
amdgpu_discovery.c - patch #10
is embedded in a larger structure. In these cases, we can not call 
kset_put() in error path in kset_register()
itself.

Thanks,
Yang
> thanks,
>
> greg k-h
> .