angel(2) system call, the quest for immortality, aka kill(2) with SIGSTOP/SIGKILL will *not* work

[Warm White Wolf]

Greetings !

I have developed a new system call, be it named angel(2),
on Linux operating system (this is what I know), which makes
a program invulnerable to kill(2) calls, including SIGKILL and
SIGSTOP.

The uses may involve fork() + angel(), daemon() + angel(),
setsid() + angel(), exec*() + angel().

Use the intellectual property I give you, as a gift to the BSD
operating system, using 4- 3- 2- BSD licence. That's it, name
me in the sources.

Thank you, FreeBSD !
You are a great Unix operating system !
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	06. Syscalls in the linux kernel, and in the glibc library

	We write angel() system call, on a 4.14 kernel. We want immortality
	for our process (SIGKILL and SIGSTOP ignored), and if we are a daemon()
	we can obtain system-life-time processes/daemons. Note that the angel()
	syscall can be user also by user-conscious processes, which return 0;


	How I've done it :
	
	1. Changed struct task_struct, found in/usr/src/linux/include/sched.h
	by adding a int unix_deadly_signals; field. We want this to be 0, and
	to be 1, only when called by sys_angel() == angel().
	In include/sched.h
	
	2. For this, we must modify do_fork() / _do_fork(), so when we obtain
	p = copy_process(), right after it p->unix_deadly_signals = 0;
	In kernel/fork.c

	3. Remember for what we have created sys_angel() : if someone sends,
	using kill(2) system call, SIGSTOP or SIGKILL signal to our process,
	he must fail. Look in kernel/signal.c, there is a function
	do_sigaction(), and we modify :
		if (info == SEND_SIG_FORCED && t->unix_deadly_signals == 1)
			return (ret = 0);

	4. In kernel/sys.c, or another file, we SYSCALL_DEFINE0(angel) {
		current -> unix_deadly_signals = 1;
		return 0;
	}

	5. In syscall_64.tbl, the 333-th system call for 332-system calls
	original 4.14.11 Linux kernel, is :
		333	common		angel		sys_angel

	6. In include/linux/syscalls.h, add to the end of the file, right
	before #endif,
		asmlinkage long sys_angel(void);

	7. In userspace, the following test program, against SIGKILL == 9
	and SIGSTOP == 19 (and other signals I guess, but why I do not know
	why):
		#include <unistd.h>
		#include <sys/syscall.h>

		int main()
		{
			syscall(333);
			sleep(66);
			return 0;
		}

	Compile it : $ gcc angel.c -o angel
	Run it     : $ ./angel &
        Test it    : $ killall angel
	It exists  : $ jobs
		[1]+ Running 		./angel &

	8. Conclusion : IT WORKS.
	9. What remains to do : to write a wrapper in glibc, and compile the
	glibc, by the rules of glibc, as we
	10. Compiled our Linux kernel.


	whitewolf, 2017/2018
	
	other sources : 
	    http://alexandria-kewl-things.blogspot.ro/2017/
	    08/operating-systems-unix-myth-bypassed.html