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 <cneirabustos@xxxxxxxxx>
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
