[PATCH hotfix 6.12 0/8] fix error handling in mmap_region() and refactor

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

The mmap_region() function is somewhat terrifying, with spaghetti-like
control flow and numerous means by which issues can arise and incomplete
state, memory leaks and other unpleasantness can occur.

A large amount of the complexity arises from trying to handle errors late
in the process of mapping a VMA, which forms the basis of recently observed
issues with resource leaks and observable inconsistent state.

This series goes to great lengths to simplify how mmap_region() works and
to avoid unwinding errors late on in the process of setting up the VMA for
the new mapping, and equally avoids such operations occurring while the VMA
is in an inconsistent state.

The first four patches are intended for backporting to correct the
possibility of people encountering corrupted state while invoking mmap()
which is otherwise at risk of happening.

After this we go further, refactoring the code, placing it in mm/vma.c in
order to make it eventually userland testable, and significantly
simplifying the logic to avoid this issue arising in future.

Lorenzo Stoakes (8):
  mm: avoid unsafe VMA hook invocation when error arises on mmap hook
  mm: unconditionally close VMAs on error
  mm: refactor map_deny_write_exec()
  mm: resolve faulty mmap_region() error path behaviour
  tools: testing: add additional vma_internal.h stubs
  mm: insolate mmap internal logic to mm/vma.c
  mm: refactor __mmap_region()
  mm: do not attempt second merge for file-backed VMAs

 include/linux/mman.h             |  21 +-
 mm/internal.h                    |  44 ++++
 mm/mmap.c                        | 262 ++------------------
 mm/mprotect.c                    |   2 +-
 mm/nommu.c                       |   7 +-
 mm/vma.c                         | 403 ++++++++++++++++++++++++++++++-
 mm/vma.h                         | 101 +-------
 mm/vma_internal.h                |   5 +
 tools/testing/vma/vma_internal.h | 106 +++++++-
 9 files changed, 591 insertions(+), 360 deletions(-)

--
2.47.0