Re: [PATCH] seccomp: add ptrace commands for suspend/resume

On Tue, Jun 02, 2015 at 12:36:16PM +0300, Andrey Wagin wrote:

2015-06-01 22:28 GMT+03:00 Tycho Andersen [off-list ref]:

quoted

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 command, PTRACE_SUSPEND_SECCOMP that enables a
task from the init user namespace which has CAP_SYS_ADMIN to disable (and
re-enable) seccomp filters for another task so that they can be
successfully dumped (and restored).

Do we need to re-enable seccomp if a tracer detaches unexpectedly.
CRIU can be killed and we should try to not affect the task state even
in this case.

Yes, I think Pavel's suggestion on the CRIU list of simply
automatically re-enabling seccomp on ptrace detach is the right way to
go here; it should cover this case. The only question is whether or
not to leave the explicit ability to re-enable seccomp before detach
or not. I don't think it's necessary for CRIU, so perhaps I'll remove
it in the next version.

Tycho