commit 13c4a90119d28cfcb6b5bdd820c233b86c2b0237

Author: Tycho Andersen <tycho.andersen@canonical.com>

Date:   Sat Jun 13 09:02:48 2015 -0600

    seccomp: add ptrace options for suspend/resume

    This patch is the first step in enabling checkpoint/restore of processes

    with seccomp enabled.

    One of the things CRIU does while dumping tasks is inject code into them

    via ptrace to collect information that is only available to the process

    itself. However, if we are in a seccomp mode where these processes are

    prohibited from making these syscalls, then what CRIU does kills the task.

    This patch adds a new ptrace option, PTRACE_O_SUSPEND_SECCOMP, that enables

    a task from the init user namespace which has CAP_SYS_ADMIN and no seccomp

    filters to disable (and re-enable) seccomp filters for another task so that

    they can be successfully dumped (and restored). We restrict the set of

    processes that can disable seccomp through ptrace because although today

    ptrace can be used to bypass seccomp, there is some discussion of closing

    this loophole in the future and we would like this patch to not depend on

    that behavior and be future proofed for when it is removed.

    Note that seccomp can be suspended before any filters are actually

    installed; this behavior is useful on criu restore, so that we can suspend

    seccomp, restore the filters, unmap our restore code from the restored

    process' address space, and then resume the task by detaching and have the

    filters resumed as well.