linux-kernel - Re: For review: seccomp_user

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Date:   Thu, 29 Oct 2020 02:11:39 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Tycho Andersen <tycho@...ho.pizza>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        linux-man <linux-man@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Will Drewry <wad@...omium.org>, bpf <bpf@...r.kernel.org>,
        Song Liu <songliubraving@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andy Lutomirski <luto@...capital.net>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Robert Sesek <rsesek@...gle.com>
Subject: Re: For review: seccomp_user_notif(2) manual page

On Wed, Oct 28, 2020 at 11:56 PM Kees Cook <keescook@...omium.org> wrote:
> On Mon, Oct 26, 2020 at 11:31:01AM +0100, Jann Horn wrote:
> > Or I guess we could also just set O_NONBLOCK on the fd by default?
> > Since the one existing user is eventloop-based...
>
> I thought about that initially, but it rubs me the wrong way: it
> violates least-surprise for me. File descriptors are expected to be
> default-blocking. It *is* a special fd, though, so maybe it could work.
> The only case I can think of it would break would be ioctl-loop case
> that is already buggy in that it didn't handle non-zero returns?

We don't have any actual users that use the API that way outside of
the kernel's selftest/sample code, right?