Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Feb 15, 2022 at 12:45 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Tue, Feb 15, 2022 at 12:37 PM Andrew Morton
> <akpm@linux-foundation.org> wrote:
> >
> > On Tue, 15 Feb 2022 12:19:22 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > > After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset,
> > > otherwise it points to a vma that was freed and when reused leads to
> > > a use-after-free bug.
> > >
> > > ...
> > >
> > > --- a/mm/mmap.c
> > > +++ b/mm/mmap.c
> > > @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm)
> > >               vma = remove_vma(vma);
> > >               cond_resched();
> > >       }
> > > +     mm->mmap = NULL;
> > >       mmap_write_unlock(mm);
> > >       vm_unacct_memory(nr_accounted);
> > >  }
> >
> > https://lore.kernel.org/all/00000000000072ef2c05d7f81950@google.com/
> >
> > It would be nice to have a Fixes: for this.
>
> Oh, right. Should be:
>
> Fixes: 64591e8605d6 ("mm: protect free_pgtables with mmap_lock write
> lock in exit_mmap")

Andrew, do you want me to post another version with Fixes:
64591e8605d6 ("mm: protect free_pgtables with mmap_lock write lock in
exit_mmap") added or you can add it directly?


>
> >
> > Is it specific to process_mrelease(), or should we backport further?
>
> The broken change is recent and was introduced in v5.17-rc1.