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

Kyle Huey
2021-11-17T16:24:47Z

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