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From:   Kyle Huey <me@kylehuey.com>
Date:   Wed, 17 Nov 2021 08:24:28 -0800
Message-ID: <CAP045AqSKv8hAz79ntbj6ZoGiO-v7M0UBuQF2hwJdXqqL7oxWA@mail.gmail.com>
Subject: Re: [PATCH 0/3] signal: requeuing undeliverable signals
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Peter Zijlstra <peterz@infradead.org>,
        Marco Elver <elver@google.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Collingbourne <pcc@google.com>,
        Alexey Gladkov <legion@kernel.org>,
        "Robert O'Callahan" <rocallahan@gmail.com>,
        =?UTF-8?B?TWFya28gTcOka2Vsw6Q=?= <marko.makela@mariadb.com>,
        Linux API <linux-api@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>
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On Mon, Nov 15, 2021 at 9:31 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>
> Kyle Huey recently reported[1] that rr gets confused if SIGKILL prevents
> ptrace_signal from delivering a signal, as the kernel setups up a signal
> frame for a signal that rr did not have a chance to observe with ptrace.
>
> In looking into it I found a couple of bugs and a quality of
> implementation issue.
>
> - The test for signal_group_exit should be inside the for loop in get_signal.
> - Signals should be requeued on the same queue they were dequeued from.
> - When a fatal signal is pending ptrace_signal should not return another
>   signal for delivery.
>
> Kyle Huey has verified[2] an earlier version of this change.
>
> I have reworked things one more time to completely fix the issues
> raised, and to keep the code maintainable long term.
>
> I have smoke tested this code and combined with a careful review I
> expect this code to work fine.  Kyle if you can double check that
> my last round of changes still works for rr I would appreciate it.

This still fixes the race we reported.

Tested-by: Kyle Huey <khuey@kylehuey.com>

- Kyle

> Eric W. Biederman (3):
>       signal: In get_signal test for signal_group_exit every time through the loop
>       signal: Requeue signals in the appropriate queue
>       signal: Requeue ptrace signals
>
>  fs/signalfd.c                |  5 +++--
>  include/linux/sched/signal.h |  7 ++++---
>  kernel/signal.c              | 44 ++++++++++++++++++++++++++------------------
>  3 files changed, 33 insertions(+), 23 deletions(-)
>
> [1] https://lkml.kernel.org/r/20211101034147.6203-1-khuey@kylehuey.com
> [2] https://lkml.kernel.org/r/CAP045ApAX725ZfujaK-jJNkfCo5s+oVFpBvNfPJk+DKY8K7d=Q@mail.gmail.com
>
> Eric