mmaped data is never unmapped

[danielsn]

Problem:

s2n_stuffer_alloc_ro_from_fd does an mmap, but that data is never unmapped

• there are in fact no calls to munmap in the codebase https://github.com/awslabs/s2n/search?q=munmap&unscoped_q=munmap

Solution:

unmap the data

Note that this may not be a huge problem, since it only has one caller:
https://github.com/awslabs/s2n/search?q=s2n_stuffer_alloc_ro_from_fd&unscoped_q=s2n_stuffer_alloc_ro_from_fd
which appears to have no callers
https://github.com/awslabs/s2n/search?q=s2n_stuffer_alloc_ro_from_file&unscoped_q=s2n_stuffer_alloc_ro_from_file

• Does this change what S2N sends over the wire? If yes, explain.
• Does this change any public APIs? If yes, explain.
• Which versions of TLS will this impact?

Requirements / Acceptance Criteria:

What must a solution address in order to solve the problem? How do we know the solution is complete?

• RFC links: Links to relevant RFC(s)
• Related Issues: Link any relevant issues
• Will the Usage Guide or other documentation need to be updated?
• Testing: How will this change be tested? Call out new integration tests, functional tests, or particularly interesting/important unit tests.
  • Will this change trigger SAW changes? Changes to the state machine, the s2n_handshake_io code that controls state transitions, the DRBG, or the corking/uncorking logic could trigger SAW failures.
  • Should this change be fuzz tested? Will it handle untrusted input? Create a separate issue to track the fuzzing work.

Out of scope:

Is there anything the solution will intentionally NOT address?