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Date:   Wed, 17 Nov 2021 15:24:24 -0800
From:   Linus Torvalds <>
To:     Kees Cook <>
Cc:     "Eric W. Biederman" <>,
        Kyle Huey <>,
        Andrea Righi <>,
        Shuah Khan <>,
        Alexei Starovoitov <>,
        Andy Lutomirski <>,
        Will Drewry <>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <>, bpf <>,
        open list <>,,
        "Robert O'Callahan" <>
Subject: Re: [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers

On Wed, Nov 17, 2021 at 1:54 PM Kees Cook <> wrote:
> The SA_IMMUTABLE change was to deal with failures seen in the seccomp
> test suite after the recent fatal signal refactoring. Mainly that a
> process that should have effectively performed do_exit() was suddenly
> visible to the tracer.

I think this basically shows that the conversion from do_exit() to
fatal_signal() was just wrong. The "do_exit()" wasn't really a signal,
and can't be treated as such.

That said, instead of reverting, maybe we can just mark the cases
where it really is about sending a synchronous signal, vs sending an
explicitly fatal signal.

It's basically the "true" condition to force_sig_info_to_task(), so
the fix might be just

  @@ -1323,7 +1323,8 @@ force_sig_info_to_task(struct kernel_siginfo
*info, struct task_struct *t, bool
        blocked = sigismember(&t->blocked, sig);
        if (blocked || ignored || sigdfl) {
                action->sa.sa_handler = SIG_DFL;
  -             action->sa.sa_flags |= SA_IMMUTABLE;
  +             if (sigdfl)
  +                     action->sa.sa_flags |= SA_IMMUTABLE;
                if (blocked) {
                        sigdelset(&t->blocked, sig);

Kyle, does that fix your test-case? And Kees - yours?


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