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

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Date:   Mon, 15 Nov 2021 23:29:11 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Kyle Huey <me@...ehuey.com>, 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@...r.kernel.org>, Al Viro <viro@...IV.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH 0/3] signal: requeuing undeliverable signals


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.

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