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

[Luben Tuikov <luben.tuikov@amd.com>]

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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.

Regards,
Luben

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From 71e0a22801c0699f67ea40ed96e0a7d7d9e0f318 Mon Sep 17 00:00:00 2001
From: Luben Tuikov <luben.tuikov@amd.com>
Date: Fri, 21 Oct 2022 03:34:21 -0400
Subject: [PATCH] kobject: Add kset_put() if kset_register() fails
X-check-string-leak: v1.0

If kset_register() fails, we call kset_put() before returning the
error. This makes sure that we free memory allocated by kobj_set_name()
for the kset, since kset_register() cannot be called unless the kset has
a name, usually gotten via kobj_set_name(&kset->kobj, format, ...);

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
---
 lib/kobject.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index a0b2dbfcfa2334..c122b979f2b75e 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -844,8 +844,10 @@ int kset_register(struct kset *k)
 
 	kset_init(k);
 	err = kobject_add_internal(&k->kobj);
-	if (err)
+	if (err) {
+		kset_put(k);
 		return err;
+	}
 	kobject_uevent(&k->kobj, KOBJ_ADD);
 	return 0;
 }
-- 
2.38.0-rc2


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