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

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Date:   Thu, 18 Nov 2021 08:12:24 +0200
From:   Marko Mäkelä <marko.makela@...iadb.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Kyle Huey <me@...ehuey.com>,
        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>,
        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

On Wed, Nov 17, 2021 at 6:51 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> 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

Thank you, Kyle and Eric, for reporting and fixing the root cause of this race.

Meanwhile, I followed Kyle's suggestion and will disable the crash
handlers in the tracee whenever it is being traced.

Marko
-- 
Marko Mäkelä, Lead Developer InnoDB
MariaDB Corporation