Re: [PATCH 3/4] seccomp: Add SECCOMP_USER_NOTIF_FLAG_PIDFD to get pidfd on listener trap

On Fri, May 15, 2020 at 04:49:14AM -0700, Sargun Dhillon wrote:

On Sat, Jan 25, 2020 at 9:42 PM Tycho Andersen [off-list ref] wrote:

quoted

On Fri, Jan 24, 2020 at 12:09:37PM -0800, Sargun Dhillon wrote:

quoted

On Fri, Jan 24, 2020 at 10:03 AM Tycho Andersen [off-list ref] wrote:

quoted

On Fri, Jan 24, 2020 at 01:17:42AM -0800, Sargun Dhillon wrote:

quoted

Currently, this just opens the group leader of the thread that

triggere

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the event, as pidfds (currently) are limited to group leaders.

I don't love the semantics of this; when they're not limited to thread
group leaders any more, we won't be able to change this. Is that work
far off?

Tycho

We would be able to change this in the future if we introduced a flag

like

quoted

SECCOMP_USER_NOTIF_FLAG_PIDFD_THREAD which would send a
pidfd that's for the thread, and not just the group leader. The flag

could

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either be XOR with SECCOMP_USER_NOTIF_FLAG_PIDFD, or
could require both. Alternatively, we can rename
SECCOMP_USER_NOTIF_FLAG_PIDFD to
SECCOMP_USER_NOTIF_FLAG_GROUP_LEADER_PIDFD.

Ok, but then isn't this just another temporary API? Seems like it's
worth waiting until the Right Way exists.

Tycho

It's been a few months. It does not appear like much progress has been made
moving away from
pidfd being only useful for leaders.

I would either like to respin this patch, or at a minimum, include the
process group leader pid number
in the seccomp notification, to simplify things for tracers.

I'd prefer if you went with the second option where you include the
process group leader pid number.
I'm against adding countless ways of producing pidfds through various
unrelated apis. The api is still quite fresh so I'd like to not overdo
it.

Christian