[0/5] fs: Do not allow get_file() to resurrect 0 f_count

Message

Kees Cook May 2, 2024, 10:33 p.m. UTC

Hi,

Failure with f_count reference counting are better contained by
an actual reference counting type, like refcount_t. The first step
is for get_file() to use inc_not_zero to avoid resurrection. I also
found a couple open-coded modifications of f_count that should be using
get_file(). Since long ago, f_count was switched to atomic_long_t, so to
get proper reference count checking, I've added a refcount_long_t API,
and then converted f_count to refcount_long_t.

Now if there are underflows (or somehow an overflow), we'll see them
reported.

-Kees

Kees Cook (5):
  fs: Do not allow get_file() to resurrect 0 f_count
  drm/vmwgfx: Do not directly manipulate file->f_count
  drm/i915: Do not directly manipulate file->f_count
  refcount: Introduce refcount_long_t and APIs
  fs: Convert struct file::f_count to refcount_long_t

 MAINTAINERS                           |   2 +-
 Makefile                              |  11 +-
 drivers/gpu/drm/i915/gt/shmem_utils.c |   5 +-
 drivers/gpu/drm/vmwgfx/ttm_object.c   |   2 +-
 fs/file.c                             |   4 +-
 fs/file_table.c                       |   6 +-
 include/linux/fs.h                    |   7 +-
 include/linux/refcount-impl.h         | 344 ++++++++++++++++++++++++++
 include/linux/refcount.h              | 341 +------------------------
 include/linux/refcount_types.h        |  12 +
 lib/refcount.c                        |  17 +-
 11 files changed, 398 insertions(+), 353 deletions(-)
 create mode 100644 include/linux/refcount-impl.h