[PATCH bpf-next v10 0/4] BPF: New helper to obtain namespace data from current task

[Carlos Neira <cneirabustos@gmail.com>]

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

Changes from v9 :
Removed samples/bpf in favor of tools/testing/selftests/bpf
Fixed bug when bpf helper is called in an interrupt context.
Code style fixes.
Added more comments on bpf helper struct member.

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

Carlos Neira (4):
  fs/namei.c: make available filename_lookup() for bpf helpers.
  bpf: new helper to obtain namespace data from  current task New bpf
    helper bpf_get_current_pidns_info.
  tools: Added bpf_get_current_pidns_info  helper.
  tools/testing/selftests/bpf: Add self-tests  for helper
    bpf_get_pidns_info.

 fs/internal.h                                      |   2 -
 fs/namei.c                                         |   1 -
 include/linux/bpf.h                                |   1 +
 include/linux/namei.h                              |   4 +
 include/uapi/linux/bpf.h                           |  35 ++++-
 kernel/bpf/core.c                                  |   1 +
 kernel/bpf/helpers.c                               |  86 ++++++++++++
 kernel/trace/bpf_trace.c                           |   2 +
 tools/include/uapi/linux/bpf.h                     |  35 ++++-
 tools/testing/selftests/bpf/Makefile               |   2 +-
 tools/testing/selftests/bpf/bpf_helpers.h          |   3 +
 .../testing/selftests/bpf/progs/test_pidns_kern.c  |  52 ++++++++
 .../selftests/bpf/progs/test_pidns_nmi_kern.c      |  52 ++++++++
 tools/testing/selftests/bpf/test_pidns.c           | 146 +++++++++++++++++++++
 tools/testing/selftests/bpf/test_pidns_nmi.c       | 139 ++++++++++++++++++++
 15 files changed, 555 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_pidns_kern.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pidns_nmi_kern.c
 create mode 100644 tools/testing/selftests/bpf/test_pidns.c
 create mode 100644 tools/testing/selftests/bpf/test_pidns_nmi.c

-- 
2.11.0