[PATCH v6 0/6] Improved seccomp logging

[Tyler Hicks <tyhicks@canonical.com>]

This patch set aims to improve logging in seccomp by:

 1) Empowering administrators to be able to permit or quiet logging of
    specific seccomp actions
 2) Allowing applications to request logging of all actions, except for
    RET_ALLOW, in the filter being loaded (subject to the
    administrator's wishes in #1)
 3) By making it possible for application developers to request logging
    of specific syscalls while developing filters for their application
    (subject to the administrator's wishes in #1)

With this patch set applied, the logic for deciding if an action will be
logged is as described in the commit message of the final patch.

* Changes since v5:
  - Rebase onto
    https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/?h=seccomp/kill_process
    (kees)
    + Redefine the value of SECCOMP_FILTER_FLAG_LOG to account for the
      new SECCOMP_FILTER_FLAG_KILL_PROCESS
    + Add SECCOMP_FILTER_FLAG_KILL_PROCESS to the
      detect_seccomp_filter_flags selftest
  - Reorder patches to move SECCOMP_GET_ACTION_AVAIL patch behind
    actions_avail sysctl patch (kees)
  - Reorder patches to move the selftest to detect filter flag support
    before the patch that adds SECCOMP_FILTER_FLAG_LOG (kees)
  - Add psuedo code showing the high level logic of when and when not to
    log to the commit message of each patch that changes the logging
    behavior (inspired by kees)
  - Add Suggested-by to the SECCOMP_GET_ACTION_AVAIL patch to credit
    Andy for the idea (tyhicks)
  - Use sizeof(seccomp_actions_avail), instead of strlen(), to avoid
    variable length "names" array in seccomp_actions_logged_handler()
    (smatch)
  - Only check the actions_logged sysctl value for "kill" when first
    introducing the actions_logged sysctl since filters cannot yet set
    the FILTER_FLAG_LOG flag (kees)
  - Mention how the actions_logged sysctl could quiet SECCOMP_RET_LOG
    actions in seccomp_filter.rst documentation (kees)

Tyler