From: Christian Brauner <brauner@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Robert Święcki" <robert@swiecki.net>,
"Kees Cook" <keescook@chromium.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Jann Horn" <jannh@google.com>, "Will Drewry" <wad@chromium.org>,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [RFC] Get siginfo from unreaped task
Date: Sun, 13 Feb 2022 09:52:12 +0100 [thread overview]
Message-ID: <20220213085212.cwzuqlrabpgbnbac@wittgenstein> (raw)
In-Reply-To: <CF5167CE-FA1C-4CEC-9EA8-5EE8041FE7C4@amacapital.net>
On Sat, Feb 12, 2022 at 06:32:08PM -0800, Andy Lutomirski wrote:
>
> > On Feb 12, 2022, at 3:24 AM, Robert Święcki <robert@swiecki.net> wrote:
> >
> > sob., 12 lut 2022 o 05:28 Kees Cook <keescook@chromium.org> napisał(a):
> >>
> >> Make siginfo available through PTRACE_GETSIGINFO after process death,
> >> without needing to have already used PTRACE_ATTACH. Uses 48 more bytes
> >> in task_struct, though I bet there might be somewhere else we could
> >> stash a copy of it?
> >
> > An alternative way of accessing this info could be abusing the
> > waitid() interface, with some additional, custom to Linux, flag
> >
> > waitid(P_ALL, 0, &si, __WCHILDSIGINFO);
> >
> > which would change what is put into si.
> >
> > But maybe ptrace() is better, because it's mostly incompatible with
> > other OSes anyway on the behavior/flag level, while waitd() seems to
> > be POSIX/BSD standard, even if Linux specifies some additional flags.
> >
> >
>
> I had a kind of opposite thought, which is that it would be very nice
> to be able to get all the waitid() data without reaping a process or
> even necessarily being its parent. Maybe these can be combined? A
> new waitid() option like you’re suggesting could add siginfo (and
> might need permissions). And we could have a different waitid() flag
> that says “maybe not my child, don’t reap” (and also needs
> permissions).
>
> Although the “don’t reap” thing is fundamentally racy. What a sane
> process manager actually wants is an interface to read all this info
> from a pidfd, which means it all needs to get stuck in struct pid. And
/me briefly pops out from vacation
Agreed and not just siginfo I would expect(?). We already came to that
conclusion when we first introduced them.
> task_struct needs a completion or wait queue so you can actually wait
> for a pidfd to exit (unless someone already did this — I had patches a
> while back). And this would be awesome.
Currently, you can wait for a pidfd to exit via polling and you can use
a pidfd to pass it to waitid(P_PIDFD, pidfd, ...).
/me pops back into vacation
next prev parent reply other threads:[~2022-02-13 8:52 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-12 4:28 [RFC] Get siginfo from unreaped task Kees Cook
2022-02-12 11:23 ` Robert Święcki
2022-02-13 2:32 ` Andy Lutomirski
2022-02-13 8:52 ` Christian Brauner [this message]
2022-02-14 20:07 ` Kees Cook
2022-02-14 22:08 ` Robert Święcki
2022-02-15 9:01 ` Christian Brauner
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=20220213085212.cwzuqlrabpgbnbac@wittgenstein \
--to=brauner@kernel.org \
--cc=ebiederm@xmission.com \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=robert@swiecki.net \
--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).