Re: [BUG] hard-to-hit mm_struct UAF due to insufficiently careful vma_refcount_put() wrt SLAB_TYPESAFE_BY_RCU

[Jann Horn]

On Wed, Jul 23, 2025 at 9:52 PM Jann Horn <jannh@xxxxxxxxxx> wrote:
> I'm not sure if I'm understanding you correctly; but yes,
> __vma_enter_locked() waits for all the waiters to drop their
> "refcounts". (It's not really a refcount, you can also think of it as
> a sleepable read-write lock where the low bits are the number of
> readers.)

Sorry, that's not entirely true, since an attached VMA has a refcount
elevated by one. It's kind of a refcount, and kind of forms part of a
sleepable read-write lock, it's complicated.