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

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Oct 21, 2022 at 03:55:18AM -0400, Luben Tuikov wrote:
> On 2022-10-21 01:37, 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F0db486eb-6927-927e-3629-958f8f211194%40huawei.com%2FT%2F&data=05%7C01%7Cluben.tuikov%40amd.com%7C65b33f087ef245a9f23708dab3264840%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019274318153227%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=1ZoieEob62iU9kI8fvpp20qGut9EeHKIHtCAT01t%2Bz8%3D&reserved=0
> >>
> >> The very first discussion on this was here:
> >>
> >> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Fdri-devel%2Fmsg368077.html&data=05%7C01%7Cluben.tuikov%40amd.com%7C65b33f087ef245a9f23708dab3264840%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019274318153227%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=9joWxGLUxZZMvrfkxCR8KbkoXifsqoMK0vGR%2FyEG62w%3D&reserved=0
> >>
> >> 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.
> 
> Looking at kset_register(), we can add kset_put() in the error path,
> when kobject_add_internal(&kset->kobj) fails.
> 
> See the attached patch. It needs to be tested with the same error injection
> as Yang has been doing.
> 
> Now, struct kset is being embedded in larger structs--see amdgpu_discovery.c
> starting at line 575. If you're on an AMD system, it gets you the tree
> structure you'll see when you run "tree /sys/class/drm/card0/device/ip_discovery/".
> That shouldn't be a problem though.

Yes, that shouldn't be an issue as the kobject embedded in a kset is
ONLY for that kset itself, the kset structure should not be controling
the lifespan of the object it is embedded in, right?

Note, the use of ksets by a device driver like you are doing here in the
amd driver is BROKEN and will cause problems by userspace tools.  Don't
do that please, just use a single subdirectory for an attribute.  Doing
deeper stuff like this is sure to cause problems and be a headache.

thanks,

greg k-h