[PATCH bpf-next V9 0/3] BPF: New helper to obtain namespace data from current task

This helper obtains the active namespace from current and returns pid, tgid,
device and namespace id as seen from that namespace, allowing to instrument
a process inside a container.
Device is read from /proc/self/ns/pid, as in the future it's possible that
different pid_ns files may belong to different devices, according
to the discussion between Eric Biederman and Yonghong in 2017 linux plumbers
conference.
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.

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.

For example a bcc script using bpf_get_current_pid_tgid() (tools/funccount.py):

        u32 pid = bpf_get_current_pid_tgid() >> 32;
        if (pid != <pid_arg_passed_in>)
                return 0;
Could be modified to use bpf_get_current_pidns_info() as follows:

        struct bpf_pidns pidns;
        bpf_get_current_pidns_info(&pidns, sizeof(struct bpf_pidns));
        u32 pid = pidns.tgid;
        u32 nsid = pidns.nsid;
        if ((pid != <pid_arg_passed_in>) && (nsid != <nsid_arg_passed_in>))
                return 0;

To find out the name PID namespace id of a process, you could use this command:

$ ps -h -o pidns -p <pid_of_interest>

Or this other command:

$ ls -Li /proc/<pid_of_interest>/ns/pid

Signed-off-by: Carlos Neira <redacted>

Carlos Neira (3):
  bpf: new helper to obtain namespace data from current task
  samples/bpf: added sample code for bpf_get_current_pidns_info.
  tools/testing/selftests/bpf: Add self-tests for new helper.

 fs/internal.h                                      |   2 -
 fs/namei.c                                         |   1 -
 include/linux/bpf.h                                |   1 +
 include/linux/namei.h                              |   4 +
 include/uapi/linux/bpf.h                           |  31 ++++-
 kernel/bpf/core.c                                  |   1 +
 kernel/bpf/helpers.c                               |  64 ++++++++++
 kernel/trace/bpf_trace.c                           |   2 +
 samples/bpf/Makefile                               |   3 +
 samples/bpf/trace_ns_info_user.c                   |  35 ++++++
 samples/bpf/trace_ns_info_user_kern.c              |  44 +++++++
 tools/include/uapi/linux/bpf.h                     |  31 ++++-
 tools/testing/selftests/bpf/Makefile               |   2 +-
 tools/testing/selftests/bpf/bpf_helpers.h          |   3 +
 .../testing/selftests/bpf/progs/test_pidns_kern.c  |  51 ++++++++
 tools/testing/selftests/bpf/test_pidns.c           | 138 +++++++++++++++++++++
 16 files changed, 407 insertions(+), 6 deletions(-)
 create mode 100644 samples/bpf/trace_ns_info_user.c
 create mode 100644 samples/bpf/trace_ns_info_user_kern.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pidns_kern.c
 create mode 100644 tools/testing/selftests/bpf/test_pidns.c

-- 
2.11.0