linux-kernel - Re: [PATCH] seccomp: Add group_leader pid to seccomp

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Message-ID: <20200518132355.GB2405879@cisco>
Date:   Mon, 18 May 2020 07:23:55 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Sargun Dhillon <sargun@...gun.me>,
        Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
        containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: 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:
> > On Sun, May 17, 2020 at 02:30:57PM -0700, Kees Cook wrote:
> > > 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