In the Linux kernel, the following vulnerability has been resolved:

binder: fix race between mmput() and do_exit()

Task A calls binder_update_page_range() to allocate and insert pages on
a remote address space from Task B. For this, Task A pins the remote mm
via mmget_not_zero() first. This can race with Task B do_exit() and the
final mmput() refcount decrement will come from Task A.

  Task A            | Task B
  ------------------+------------------
  mmget_not_zero()  |
                    |  do_exit()
                    |    exit_mm()
                    |      mmput()
  mmput()           |
    exit_mmap()     |
      remove_vma()  |
        fput()      |

In this case, the work of ____fput() from Task B is queued up in Task A
as TWA_RESUME. So in theory, Task A returns to userspace and the cleanup
work gets executed. However, Task A instead sleep, waiting for a reply
from Task B that never comes (it's dead).

This means the binder_deferred_release() is blocked until an unrelated
binder event forces Task A to go back to userspace. All the associated
death notifications will also be delayed until then.

In order to fix this use mmput_async() that will schedule the work in
the corresponding mm->async_put_work WQ instead of Task A.

kernel.org https://git.kernel.org/stable/c/252a2a5569eb9f8d16428872cc24dea1ac0bb097 [No types assigned]

kernel.org https://git.kernel.org/stable/c/6696f76c32ff67fec26823fc2df46498e70d9bf3 [No types assigned]

kernel.org https://git.kernel.org/stable/c/67f16bf2cc1698fd50e01ee8a2becc5a8e6d3a3e [No types assigned]

kernel.org https://git.kernel.org/stable/c/77d210e8db4d61d43b2d16df66b1ec46fad2ee01 [No types assigned]

kernel.org https://git.kernel.org/stable/c/7e7a0d86542b0ea903006d3f42f33c4f7ead6918 [No types assigned]

kernel.org https://git.kernel.org/stable/c/95b1d336b0642198b56836b89908d07b9a0c9608 [No types assigned]

kernel.org https://git.kernel.org/stable/c/98fee5bee97ad47b527a997d5786410430d1f0e9 [No types assigned]

kernel.org https://git.kernel.org/stable/c/9a9ab0d963621d9d12199df9817e66982582d5a5 [No types assigned]