bpf: introduce BPF_CGROUP_FILE_OPEN

Hi All,

Similar to networking sandboxing programs and cgroup-v2 based hooks (BPF_CGROUP_INET_[INGRESS|EGRESS,] BPF_CGROUP_INET[4|6]_[BIND|CONNECT], etc) introduce basic per-container sandboxing for file access via
new BPF_PROG_TYPE_FILE_FILTER program type that attaches after security_file_open() LSM hook and works as additional file_open filter. The new cgroup bpf hook is called BPF_CGROUP_FILE_OPEN.

Just like other cgroup-bpf programs new BPF_PROG_TYPE_FILE_FILTER type is only available to root.

Use cases:
- disallow certain FS types within containers (fs_magic == CGROUP2_SUPER_MAGIC)
- restrict permissions in particular mount (mnt_id == X && (flags & O_RDWR))
- disallow access to hard linked sensitive files (nlink > 1 && mode == 0700)
- disallow access to world writeable files (mode == 0..7)
- disallow access to given set of files (dev_major == X && dev_minor == Y && inode == Z)

Alexei Starovoitov (6):
bpf: introduce BPF_PROG_TYPE_FILE_FILTER
fs: wire in BPF_CGROUP_FILE_OPEN hook tools/bpf: sync uapi/bpf.h
trace/bpf: allow %o modifier in bpf_trace_printk
libbpf: support BPF_CGROUP_FILE_OPEN in libbpf selftests/bpf: add a test for BPF_CGROUP_FILE_OPEN

 fs/open.c                                     |   4 +
 include/linux/bpf-cgroup.h                    |  10 +
 include/linux/bpf_types.h                     |   1 +
 include/uapi/linux/bpf.h                      |  28 ++-
 kernel/bpf/cgroup.c                           | 171 ++++++++++++++++++
 kernel/bpf/syscall.c                          |   7 +
 kernel/trace/bpf_trace.c                      |   2 +-
 tools/include/uapi/linux/bpf.h                |  28 ++-
 tools/lib/bpf/libbpf.c                        |   3 +
 tools/testing/selftests/bpf/.gitignore        |   1 +
 tools/testing/selftests/bpf/Makefile          |   6 +-
 tools/testing/selftests/bpf/bpf_helpers.h     |   2 +
 tools/testing/selftests/bpf/test_file_open.c  | 154 ++++++++++++++++
 .../selftests/bpf/test_file_open_common.h     |  13 ++
 .../selftests/bpf/test_file_open_kern.c       |  48 +++++
 15 files changed, 473 insertions(+), 5 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/test_file_open.c
 create mode 100644 tools/testing/selftests/bpf/test_file_open_common.h
 create mode 100644 tools/testing/selftests/bpf/test_file_open_kern.c

2.17.1