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From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Jann Horn <jannh@google.com>
Cc: mtk.manpages@gmail.com, Tycho Andersen <tycho@tycho.pizza>,
	Sargun Dhillon <sargun@sargun.me>,
	Kees Cook <keescook@chromium.org>,
	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: Mon, 26 Oct 2020 10:47:53 +0100	[thread overview]
Message-ID: <a1921621-6656-c440-2117-2e5f1d31dafd@gmail.com> (raw)
In-Reply-To: <CAG48ez2TcWb6SQ86XRJDdN-Ab_gO9-sXgpFnJODMXH60mCkBJQ@mail.gmail.com>

Hi Jann,

On 10/26/20 10:32 AM, Jann Horn wrote:
> On Sat, Oct 24, 2020 at 2:53 PM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
>> On 10/17/20 2:25 AM, Jann Horn wrote:
>>> On Fri, Oct 16, 2020 at 8:29 PM Michael Kerrisk (man-pages)
>>> <mtk.manpages@gmail.com> wrote:
> [...]
>>>> I'm not sure if I should write anything about this small UAPI
>>>> breakage in BUGS, or not. Your thoughts?
>>>
>>> Thinking about it a bit more: Any code that relies on pause() or
>>> epoll_wait() not restarting is buggy anyway, right? Because a signal
>>> could also arrive directly before entering the syscall, while
>>> userspace code is still executing? So one could argue that we're just
>>> enlarging a preexisting race. (Unless the signal handler checks the
>>> interrupted register state to figure out whether we already entered
>>> syscall handling?)
>>
>> Yes, that all makes sense.
>>
>>> If userspace relies on non-restarting behavior, it should be using
>>> something like epoll_pwait(). And that stuff only unblocks signals
>>> after we've already past the seccomp checks on entry.
>>
>> Thanks for elaborating that detail, since as soon as you talked
>> about "enlarging a preexisting race" above, I immediately wondered
>> sigsuspend(), pselect(), etc.
>>
>> (Mind you, I still wonder about the effect on system calls that
>> are normally nonrestartable because they have timeouts. My
>> understanding is that the kernel doesn't restart those system
>> calls because it's impossible for the kernel to restart the call
>> with the right timeout value. I wonder what happens when those
>> system calls are restarted in the scenario we're discussing.)
> 
> Ah, that's an interesting edge case...

I'm going to drop a FIXME into the page source so that
there's a reminder of this issue in the next draft of 
the page, which I'm about to send out.

[...]

Thanks for checking the other pieces, Jann.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

  reply	other threads:[~2020-10-26  9:49 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
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) [this message]
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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