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

>
> Is it specific to process_mrelease(), or should we backport further?

The broken change is recent and was introduced in v5.17-rc1.

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