[PATCH bpf-next 0/2] Allow storing referenced struct file kptrs in BPF maps

[Justin Suess <utilityemal77@gmail.com>]

Hello,

This series adds a destructor for struct file, enabling it to be used as a
referenced kptr in BPF maps.

The destructor mirrors bpf_put_file() semantics and releases the reference
via fput(). This allows pointers returned from kfuncs such as
bpf_get_task_exe_file() to be safely stored and later reused with helpers
and kfuncs that operate on struct file.

This fills a gap compared to bpf_dynptr_from_file(), where the resulting
dynptr can be stored in a map, but cannot be passed to kfuncs expecting
a struct file *.

Use cases include caching file references across events and deferring
processing while keeping the underlying file alive.

Patch 1 adds the struct file kptr destructor and wires it into the BTF
kfunc sets.

Patch 2 adds selftests covering successful use and verifier rejection of
unreferenced pointers.

Justin Suess (2):
  bpf: Implement dtor for struct file BTF ID
  selftests/bpf: Add test for map-stored struct file kptrs

 kernel/bpf/helpers.c                          |  16 +-
 .../bpf/prog_tests/refcounted_kptr_file.c     | 246 ++++++++++++++++++
 .../bpf/progs/refcounted_kptr_file.c          | 152 +++++++++++
 .../bpf/progs/refcounted_kptr_file_fail.c     |  35 +++
 4 files changed, 448 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/refcounted_kptr_file.c
 create mode 100644 tools/testing/selftests/bpf/progs/refcounted_kptr_file.c
 create mode 100644 tools/testing/selftests/bpf/progs/refcounted_kptr_file_fail.c

-- 
2.53.0