linux-kernel - Re: [PATCH 0/3] signal: requeuing undeliverable signals

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Date:   Wed, 17 Nov 2021 10:51:03 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kyle Huey <me@...ehuey.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Peter Zijlstra <peterz@...radead.org>,
        Marco Elver <elver@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        Alexey Gladkov <legion@...nel.org>,
        "Robert O'Callahan" <rocallahan@...il.com>,
        Marko Mäkelä <marko.makela@...iadb.com>,
        Linux API <linux-api@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 0/3] signal: requeuing undeliverable signals

Kyle Huey <me@...ehuey.com> writes:

> On Mon, Nov 15, 2021 at 9:31 PM Eric W. Biederman <ebiederm@...ssion.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@...ehuey.com>

Thank you very much for retesting.

Eric