From: Andy Lutomirski <luto@amacapital.net>
To: "Robert Święcki" <robert@swiecki.net>
Cc: 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: Sat, 12 Feb 2022 18:32:08 -0800 [thread overview]
Message-ID: <CF5167CE-FA1C-4CEC-9EA8-5EE8041FE7C4@amacapital.net> (raw)
In-Reply-To: <CAP145phC6S6Zda-ZWLH1s4ZfDPh79rtf_7vzs-yvt1vykUCP4A@mail.gmail.com>
> 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 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.
next prev parent reply other threads:[~2022-02-13 2:32 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 [this message]
2022-02-13 8:52 ` Christian Brauner
2022-02-14 20:07 ` Kees Cook
2022-02-14 22:08 ` Robert Święcki
2022-02-15 9:01 ` Christian Brauner
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