Re: [PATCH] seccomp: Add group_leader pid to seccomp_notif

On Mon, May 18, 2020 at 02:45:00PM +0200, Christian Brauner wrote:

On Mon, May 18, 2020 at 08:32:25AM +0000, Sargun Dhillon wrote:

quoted

On Sun, May 17, 2020 at 02:30:57PM -0700, Kees Cook wrote:

quoted

On Sun, May 17, 2020 at 09:02:15AM -0600, Tycho Andersen wrote:

I'm going read this thread more carefully tomorrow, but I just wanted to
mention that I'd *like* to extend seccomp_data for doing deep argument
inspection of the new syscalls. I think it's the least bad of many
designs, and I'll write that up in more detail. (I would *really* like
to avoid extending seccomp's BPF language, and instead allow probing
into the struct copied from userspace, etc.)

Anyway, it's very related to this, so, yeah, probably we need a v2 of the
notif API, but I'll try to get all the ideas here collected in one place.

I scratched together a proposal of what I think would make a not-terrible
V2 API. I'm sure there's bugs in this code, but I think it's workable --
or at least a place to start. The biggest thing I think we should consider
is unrolling seccomp_data if we don't intend to add new BPF-accessible
fields.

If also uses read(2), so we get to take advantage of read(2)'s ability
to pass a size along with the read, as opposed to doing ioctl tricks.
It also makes programming from against it slightly simpler. I can imagine
that the send API could be similar, in that it could support write, and
thus making it 100% usable from Go (and the like) without requiring
a separate OS-thread be spun up to interact with the listener.

I don't have strong feelings about using read() and write() here but I
think that Jann had reservations and that's why we didn't do it in the
first version. But his reservations were specifically tied to fd passing
which we never implemented:
http://lkml.iu.edu/hypermail/linux/kernel/1806.2/05995.html

But still, worth considering.

There was a thread about this same time for some other API (I can't
find it now, but I can dig if you want) that suggests that "read() is
for data" and we shouldn't use it for control in APIs.

Tycho