Re: [PATCH v3 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd

On Wed, 17 Oct 2018 23:59:07 -0700, "Joel Fernandes (Google)" said:

This usecase cannot be implemented with the existing F_SEAL_WRITE seal. To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal which prevents any future mmap and write syscalls from succeeding while keeping the existing mmap active. The following program shows the seal working in action:

What is supposed to happen if some other process has an already existing R/W mmap of the region? (For that matter, the test program doesn't seem to actually test that the existing mmap region remains writable?)