linux-kernel - Re: [PATCH] mm: memory_hotplug: fix memory error handling

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Date:   Mon, 30 May 2022 09:10:27 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        cheloha@...ux.vnet.ibm.com, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux- stable <stable@...r.kernel.org>
Subject: Re: [PATCH] mm: memory_hotplug: fix memory error handling

On 30.05.22 09:08, Muchun Song wrote:
> On Mon, May 30, 2022 at 2:56 PM David Hildenbrand <david@...hat.com> wrote:
>>
>> On 30.05.22 07:33, Muchun Song wrote:
>>> The device_unregister() is supposed to be used to unregister devices if
>>> device_register() has succeed.  And device_unregister() will put device.
>>> The caller should not do it again, otherwise, the first call of
>>> put_device() will drop the last reference count, then the next call
>>> of device_unregister() will UAF on device.
>>>
>>> Fixes: 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup")
>>> Signed-off-by: Muchun Song <songmuchun@...edance.com>
>>> Cc: <stable@...r.kernel.org>
>>> ---
>>>  drivers/base/memory.c | 5 ++---
>>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>>> index 7222ff9b5e05..084d67fd55cc 100644
>>> --- a/drivers/base/memory.c
>>> +++ b/drivers/base/memory.c
>>> @@ -636,10 +636,9 @@ static int __add_memory_block(struct memory_block *memory)
>>>       }
>>>       ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
>>>                             GFP_KERNEL));
>>> -     if (ret) {
>>> -             put_device(&memory->dev);
>>> +     if (ret)
>>>               device_unregister(&memory->dev);
>>> -     }
>>> +
>>>       return ret;
>>>  }
>>>
>>
>> See
>>
>> https://lkml.kernel.org/r/d44c63d78affe844f020dc02ad6af29abc448fc4.1650611702.git.christophe.jaillet@wanadoo.fr
>>
> 
> I see. Good job by Christophe. Thanks David.
> 

I'm curious how both of you found that issue? Just by staring at that
code? :)

-- 
Thanks,

David / dhildenb