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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 Tested-by: Kyle Huey <khuey@kylehuey.com> Link: https://lkml.kernel.org/r/87bl2kekig.fsf_-_@email.froward.int.ebiederm.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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