BPF: New helper to obtain namespace data from current task

Currently bpf_get_current_pid_tgid(), is used to do pid filtering in bcc's
scripts but this helper returns the pid as seen by the root namespace which is
fine when a bcc script is not executed inside a container.
When the process of interest is inside a container, pid filtering will not work
if bpf_get_current_pid_tgid() is used.
This helper addresses this limitation returning the pid as it's seen by the current
namespace where the script is executing.

In the future different pid_ns files may belong to different devices, according to the
discussion between Eric Biederman and Yonghong in 2017 Linux plumbers conference.
To address that situation the helper requires inum and dev_t from /proc/self/ns/pid.
This helper has the same use cases as bpf_get_current_pid_tgid() as it can be
used to do pid filtering even inside a container.

Changes from V13:

- refactored selftests
- refactored ebpf helper

Signed-off-by: Carlos Neira <cneirabustos@gmail.com>


Carlos Neira (5):
  fs/nsfs.c: added ns_match
  bpf: added new helper bpf_get_ns_current_pid_tgid
  tools: Added bpf_get_ns_current_pid_tgid helper
  tools/testing/selftests/bpf: Add self-tests for new  helper.
  bpf_helpers_doc.py: Add struct bpf_pidns_info to known types

 fs/nsfs.c                                     |  8 ++
 include/linux/bpf.h                           |  1 +
 include/linux/proc_ns.h                       |  2 +
 include/uapi/linux/bpf.h                      | 20 +++-
 kernel/bpf/core.c                             |  1 +
 kernel/bpf/helpers.c                          | 45 +++++++++
 kernel/trace/bpf_trace.c                      |  2 +
 scripts/bpf_helpers_doc.py                    |  1 +
 tools/include/uapi/linux/bpf.h                | 20 +++-
 .../bpf/prog_tests/get_ns_current_pid_tgid.c  | 96 +++++++++++++++++++
 .../bpf/progs/get_ns_current_pid_tgid_kern.c  | 53 ++++++++++
 11 files changed, 247 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/get_ns_current_pid_tgid.c
 create mode 100644 tools/testing/selftests/bpf/progs/get_ns_current_pid_tgid_kern.c

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2.20.1