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From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: Tycho Andersen <tycho@tycho.pizza>,
	"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: Wed, 28 Oct 2020 15:53:04 -0700	[thread overview]
Message-ID: <202010281548.CCA92731F@keescook> (raw)
In-Reply-To: <CAG48ez2b-fnsp8YAR=H5uRMT4bBTid_hyU4m6KavHxDko1Efog@mail.gmail.com>

On Mon, Oct 26, 2020 at 10:51:02AM +0100, Jann Horn wrote:
> The problem is the scenario where a process is interrupted while it's
> waiting for the supervisor to reply.
> 
> 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

Oooh, yes, ew. Thanks for the illustration.

Thinking about this from userspace's least-surprise view, I would expect
the "recv" to stay "queued", in the sense we'd see this:

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: gets (stale) seccomp_notif from seccomp_fd
S: sends seccomp_notif_resp, receives ENOENT (or some better errno?)

This is not at all how things are designed internally right now, but
that behavior would work, yes?

-- 
Kees Cook

  parent reply	other threads:[~2020-10-28 22:54 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 11:07 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
2020-10-28 22:53                 ` Kees Cook [this message]
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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