Re: [PATCH] kernel/resource: Fix return code check in __request_free_mem_region

[Alistair Popple]

On Wednesday, 12 May 2021 10:16:41 PM AEST David Hildenbrand wrote:
> On 12.05.21 09:35, Alistair Popple wrote:
> > Splitting an earlier version of a patch that allowed calling
> > __request_region() while holding the resource lock into a series of
> > patches required changing the return code for the newly introduced
> > __request_region_locked().
> >
> > Unfortunately this change was not carried through to a subsequent
> > commit 56fd94919b8b ("kernel/resource: fix locking in
> > request_free_mem_region") in the series. This resulted in a
> > use-after-free due to freeing the struct resource without properly
> > releasing it. Fix this by correcting the return code check so that the
> > struct is not freed if the request to add it was successful.
> >
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Fixes: 56fd94919b8b ("kernel/resource: fix locking in 
request_free_mem_region")
> > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
> > ---
> >   kernel/resource.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 028a5ab18818..ca9f5198a01f 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -1805,7 +1805,7 @@ static struct resource 
*__request_free_mem_region(struct device *dev,
> >                               REGION_DISJOINT)
> >                       continue;
> >
> > -             if (!__request_region_locked(res, &iomem_resource, addr, 
size,
> > +             if (__request_region_locked(res, &iomem_resource, addr, 
size,
> >                                               name, 0))
> >                       break;
> >
> >
> 
> Ouch, missed that, would have expected this pops up right away when testing.

Yes, ouch indeed. I am still trying to figure out why I didn't catch this 
right away as well. I retested locally and the HMM tests do complete without 
causing an oops although they don't all pass. I guess I must have been in a 
rush and didn't check the test output properly to see if they actually passed.

> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

Thanks, and sorry for the extra noise.

> --
> Thanks,
> 
> David / dhildenb
>