linux-kernel - Re: For review: seccomp_user

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Message-ID: <202010281553.A72E162A7@keescook>
Date:   Wed, 28 Oct 2020 15:56:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jann Horn <jannh@...gle.com>
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 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?

-- 
Kees Cook