bpf: Sysctl hook

v2->v3:
- simplify C based selftests by relying on variable offset stack access.

v1->v2:
- add fs/proc/proc_sysctl.c mainteners to Cc:.

The patch set introduces new BPF hook for sysctl.

It adds new program type BPF_PROG_TYPE_CGROUP_SYSCTL and attach type BPF_CGROUP_SYSCTL.

BPF_CGROUP_SYSCTL hook is placed before calling to sysctl's proc_handler so that accesses (read/write) to sysctl can be controlled for specific cgroup and either allowed or denied, or traced.

The hook has access to sysctl name, current sysctl value and (on write only) to new sysctl value via corresponding helpers. New sysctl value can be overridden by program. Both name and values (current/new) are represented as strings same way they're visible in /proc/sys/. It is up to program to parse these strings.

To help with parsing the most common kind of sysctl value, vector of integers, two new helpers are provided: bpf_strtol and bpf_strtoul with semantic similar to user space strtol(3) and strtoul(3).

The hook also provides bpf_sysctl context with two fields:
* @write indicates whether sysctl is being read (= 0) or written (= 1);
* @file_pos is sysctl file position to read from or write to, can be overridden.

The hook allows to make better isolation for containerized applications that are run as root so that one container can't change a sysctl and affect all other containers on a host, make changes to allowed sysctl in a safer way and simplify sysctl tracing for cgroups.

Patch 1 is preliminary refactoring.
Patch 2 adds new program and attach types.
Patches 3-5 implement helpers to access sysctl name and value. Patch 6 adds file_pos field to bpf_sysctl context.
Patch 7 updates UAPI in tools.
Patches 8-9 add support for the new hook to libbpf and corresponding test. Patches 10-14 add selftests for the new hook.
Patch 15 adds support for new arg types to verifier: pointer to integer. Patch 16 adds bpf_strto{l,ul} helpers to parse integers from sysctl value. Patch 17 updates UAPI in tools.
Patch 18 updates bpf_helpers.h.
Patch 19 adds selftests for pointer to integer in verifier. Patches 20-21 add selftests for bpf_strto{l,ul}, including integration
C based test for sysctl value parsing.

Andrey Ignatov (21):
bpf: Add base proto function for cgroup-bpf programs
bpf: Sysctl hook
bpf: Introduce bpf_sysctl_get_name helper
bpf: Introduce bpf_sysctl_get_current_value helper
bpf: Introduce bpf_sysctl_{get,set}_new_value helpers
bpf: Add file_pos field to bpf_sysctl ctx
bpf: Sync bpf.h to tools/
libbpf: Support sysctl hook
selftests/bpf: Test sysctl section name selftests/bpf: Test BPF_CGROUP_SYSCTL selftests/bpf: Test bpf_sysctl_get_name helper selftests/bpf: Test sysctl_get_current_value helper selftests/bpf: Test bpf_sysctl_{get,set}_new_value helpers selftests/bpf: Test file_pos field in bpf_sysctl ctx
bpf: Introduce ARG_PTR_TO_{INT,LONG} arg types
bpf: Introduce bpf_strtol and bpf_strtoul helpers
bpf: Sync bpf.h to tools/
selftests/bpf: Add sysctl and strtoX helpers to bpf_helpers.h selftests/bpf: Test ARG_PTR_TO_LONG arg type selftests/bpf: Test bpf_strtol and bpf_strtoul helpers selftests/bpf: C based test for sysctl and strtoX

 fs/proc/proc_sysctl.c                         |   25 +-
 include/linux/bpf-cgroup.h                    |   21 +
 include/linux/bpf.h                           |    4 +
 include/linux/bpf_types.h                     |    1 +
 include/linux/filter.h                        |   16 +
 include/uapi/linux/bpf.h                      |  139 +-
 kernel/bpf/cgroup.c                           |  364 +++-
 kernel/bpf/helpers.c                          |  131 ++
 kernel/bpf/syscall.c                          |    7 +
 kernel/bpf/verifier.c                         |   30 +
 tools/include/uapi/linux/bpf.h                |  139 +-
 tools/lib/bpf/libbpf.c                        |    3 +
 tools/lib/bpf/libbpf_probes.c                 |    1 +
 tools/testing/selftests/bpf/Makefile          |    3 +-
 tools/testing/selftests/bpf/bpf_helpers.h     |   19 +
 .../selftests/bpf/progs/test_sysctl_prog.c    |   70 +
 .../selftests/bpf/test_section_names.c        |    5 +
 tools/testing/selftests/bpf/test_sysctl.c     | 1567 +++++++++++++++++
 .../testing/selftests/bpf/verifier/int_ptr.c  |  160 ++
 19 files changed, 2697 insertions(+), 8 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_sysctl_prog.c
 create mode 100644 tools/testing/selftests/bpf/test_sysctl.c
 create mode 100644 tools/testing/selftests/bpf/verifier/int_ptr.c

2.17.1