From: Jann Horn <jannh@google.com>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: Kees Cook <keescook@chromium.org>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Sargun Dhillon <sargun@sargun.me>,
Christian Brauner <christian@brauner.io>,
linux-man <linux-man@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Aleksa Sarai <cyphar@cyphar.com>,
Alexei Starovoitov <ast@kernel.org>,
Will Drewry <wad@chromium.org>, bpf <bpf@vger.kernel.org>,
Song Liu <songliubraving@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Andy Lutomirski <luto@amacapital.net>,
Linux Containers <containers@lists.linux-foundation.org>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Robert Sesek <rsesek@google.com>
Subject: Re: For review: seccomp_user_notif(2) manual page
Date: Thu, 29 Oct 2020 05:26:05 +0100 [thread overview]
Message-ID: <CAG48ez2=8RBh_2D=WRKta4n3jvfTpD90j8DA-uOFAm86fKjSzw@mail.gmail.com> (raw)
In-Reply-To: <20201029021348.GB25673@cisco>
On Thu, Oct 29, 2020 at 3:13 AM Tycho Andersen <tycho@tycho.pizza> wrote:
> > > Consider the following scenario (with supervisor "S" and target "T"; S
> > > wants to wait for events on two file descriptors seccomp_fd and
> > > other_fd):
> > >
> > > S: starts poll() to wait for events on seccomp_fd and other_fd
> > > T: performs a syscall that's filtered with RET_USER_NOTIF
> > > S: poll() returns and signals readiness of seccomp_fd
> > > T: receives signal SIGUSR1
> > > T: syscall aborts, enters signal handler
> > > T: signal handler blocks on unfiltered syscall (e.g. write())
> > > S: starts SECCOMP_IOCTL_NOTIF_RECV
> > > S: blocks because no syscalls are pending
> > >
> > > Depending on what other_fd is, this could in a worst case even lead to
> > > a deadlock (if e.g. the signal handler wants to write to stdout, but
> > > the stdout fd is hooked up to other_fd in the supervisor, but the
> > > supervisor can't consume the data written because it's stuck in
> > > seccomp handling).
> > >
> > > So we have to ensure that when existing code (like that crun code you
> > > linked to) triggers this case, SECCOMP_IOCTL_NOTIF_RECV returns
> > > immediately instead of blocking.
> >
> > Or I guess we could also just set O_NONBLOCK on the fd by default?
> > Since the one existing user is eventloop-based...
>
> I feel like it's ok to return an error from the RECV ioctl() if
> there's never going to be any more events on the fd; was there
> something fundamentally wrong with your patch here:
> https://lore.kernel.org/bpf/CAG48ez2xn+_KznEztJ-eVTsTzkbf9CVgPqaAk7TpRNAqbdaRoA@mail.gmail.com/
> ?
No, I have a new version of that about 80% done and hope to send it
out soonish. (There's some stuff around tests that I still need to
cobble together).
next prev parent reply other threads:[~2020-10-29 7:44 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 11:07 For review: seccomp_user_notif(2) manual page Michael Kerrisk (man-pages)
2020-09-30 15:03 ` Tycho Andersen
2020-09-30 15:11 ` Tycho Andersen
2020-09-30 20:34 ` Michael Kerrisk (man-pages)
2020-09-30 23:03 ` Tycho Andersen
2020-09-30 23:11 ` Jann Horn
2020-09-30 23:24 ` Tycho Andersen
2020-10-01 1:52 ` Jann Horn
2020-10-01 2:14 ` Jann Horn
2020-10-25 16:31 ` Michael Kerrisk (man-pages)
2020-10-26 15:54 ` Jann Horn
2020-10-27 6:14 ` Michael Kerrisk (man-pages)
2020-10-27 10:28 ` Jann Horn
2020-10-28 6:31 ` Sargun Dhillon
2020-10-28 9:43 ` Jann Horn
2020-10-28 17:43 ` Sargun Dhillon
2020-10-28 18:20 ` Jann Horn
2020-10-01 7:49 ` Michael Kerrisk (man-pages)
2020-10-26 0:32 ` Kees Cook
2020-10-26 9:51 ` Jann Horn
2020-10-26 10:31 ` Jann Horn
2020-10-28 22:56 ` Kees Cook
2020-10-29 1:11 ` Jann Horn
[not found] ` <20201029021348.GB25673@cisco>
2020-10-29 4:26 ` Jann Horn [this message]
2020-10-28 22:53 ` Kees Cook
2020-10-29 1:25 ` Jann Horn
2020-10-01 7:45 ` Michael Kerrisk (man-pages)
2020-10-14 4:40 ` Michael Kerrisk (man-pages)
2020-09-30 15:53 ` Jann Horn
2020-10-01 12:54 ` Christian Brauner
2020-10-01 15:47 ` Jann Horn
2020-10-01 16:58 ` Tycho Andersen
2020-10-01 17:12 ` Christian Brauner
2020-10-14 5:41 ` Michael Kerrisk (man-pages)
2020-10-01 18:18 ` Jann Horn
2020-10-01 18:56 ` Tycho Andersen
2020-10-01 17:05 ` Christian Brauner
2020-10-15 11:24 ` Michael Kerrisk (man-pages)
2020-10-15 20:32 ` Jann Horn
2020-10-16 18:29 ` Michael Kerrisk (man-pages)
2020-10-17 0:25 ` Jann Horn
2020-10-24 12:52 ` Michael Kerrisk (man-pages)
2020-10-26 9:32 ` Jann Horn
2020-10-26 9:47 ` Michael Kerrisk (man-pages)
2020-09-30 23:39 ` Kees Cook
2020-10-15 11:24 ` Michael Kerrisk (man-pages)
2020-10-26 0:19 ` Kees Cook
2020-10-26 9:39 ` Michael Kerrisk (man-pages)
2020-10-01 12:36 ` Christian Brauner
2020-10-15 11:23 ` Michael Kerrisk (man-pages)
2020-10-01 21:06 ` Sargun Dhillon
2020-10-01 23:19 ` Tycho Andersen
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