linux-kernel - Re: [PATCH v2] mm/mmu_notifier.c: Fix race in mmu_interval_notifier

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Date:   Wed, 20 Apr 2022 16:35:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        christian.koenig@....com, jhubbard@...dia.com,
        rcampbell@...dia.com, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2] mm/mmu_notifier.c: Fix race in
 mmu_interval_notifier_remove()

On Thu, 21 Apr 2022 09:21:06 +1000 Alistair Popple <apopple@...dia.com> wrote:

> >> As the wait_event() condition is true it will return immediately. This
> >> can lead to use-after-free type errors if the caller frees the data
> >> structure containing the interval notifier subscription while it is
> >> still on a deferred list. Fix this by taking the appropriate lock when
> >> reading invalidate_seq to ensure proper synchronisation.
> >>
> >> ...
> >>
> >> Fixes: 99cb252f5e68 ("mm/mmu_notifier: add an interval tree notifier")
> >
> > Do you think fix this should be backported into older kernels?
> 
> Yes, I forgot to cc stable sorry.

So we have actually seen these use-after-free errors?

Some description of the end-user visible impact is always helpful when
deciding which trees need a patch.

> Do you want me to resend with
> 'Cc: stable@...r.kernel.org'?

Thanks, I added that.