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/
next prev parent 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 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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a1921621-6656-c440-2117-2e5f1d31dafd@gmail.com \
--to=mtk.manpages@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=christian@brauner.io \
--cc=containers@lists.linux-foundation.org \
--cc=cyphar@cyphar.com \
--cc=daniel@iogearbox.net \
--cc=gscrivan@redhat.com \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=rsesek@google.com \
--cc=sargun@sargun.me \
--cc=songliubraving@fb.com \
--cc=tycho@tycho.pizza \
--cc=wad@chromium.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).