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

After the Maple tree patches, mm_struct.mmap doesn't exist. So I'll
revert this fix as part of merging the maple-tree parts of linux-next.
I'll be sending this fix to Linus this week.

All of which means that the thusly-resolved Maple tree patches might
reintroduce this use-after-free bug.

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