Re: [PATCH] mm: memory_hotplug: fix memory error handling

[Muchun Song]

On Mon, May 30, 2022 at 3:10 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 30.05.22 09:08, Muchun Song wrote:
> > On Mon, May 30, 2022 at 2:56 PM David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> >>> Cc: <stable@xxxxxxxxxxxxxxx>
> >>> ---
> >>>  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@xxxxxxxxxx
> >>
> >
> > I see. Good job by Christophe. Thanks David.
> >
>
> I'm curious how both of you found that issue? Just by staring at that
> code? :)
>

I am reading the code here today, then I saw it by chance.
No tricks :-).

THanks.