Re: [PATCH] ptrace on stopped processes (2.4)

[vic <zandy@cs.wisc.edu>]

Now I see the problem with PTRACE_KILL.  Thanks for the example.

I'm looking into it.  I need to justify the quoted portion of the
patch or find a better way to get its effect.

In the meantime, the problem could be fixed by changing the
PTRACE_KILL implementation to call send_sig instead of setting
exit_code.  How does that strike people?

More generally, could someone explain to me why there are two
mechanisms for interprocess signaling within the kernel, exit_code and
send_sig?

Thanks,
Vic
> vic <zandy@cs.wisc.edu> writes:
>
>> From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>:
>> >> --- linux-2.4.16/kernel/ptrace.c	Wed Nov 21 16:43:01 2001
>> >> +++ linux-2.4.16.1/kernel/ptrace.c	Fri Dec 21 10:42:44 2001
>> >> @@ -89,8 +89,10 @@
>> >>  		SET_LINKS(task);
>> >>  	}
>> >>  	write_unlock_irq(&tasklist_lock);
>> >> -
>> >> -	send_sig(SIGSTOP, task, 1);
>> >> +	if (task->state != TASK_STOPPED)
>> >> +		send_sig(SIGSTOP, task, 1);
>> >> +	else
>> >> +		task->exit_code = SIGSTOP;
>> >>  	return 0;
>> >>  
>> >>  bad:
>> >
>> > It seems that trace is started in the place different from
>> > usual. Then, I think PTRACE_KILL doesn't work.
>> 
>> I don't agree, it seems to work for me.
>
> I tested the following on linux-2.4.16 + your_patch:
>
> #include <stdio.h>
> #include <signal.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <sys/ptrace.h>
> #include <unistd.h>
>
> int main(int argc, char *argv[])
> {
> 	pid_t pid;
> 	int ret, status;
>
> 	pid = fork();
> 	if (pid == -1)
> 		exit(1);
> 	if (pid == 0) {
> 		raise(SIGSTOP);
> 		while (1)
> 			;
> 		_exit(1);
> 	}
>
> 	ret = waitpid(pid, &status, WUNTRACED);
> 	if (ret == -1) {
> 		perror("waitpid (1)");
> 		exit(1);
> 	}
>
> 	ret = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
> 	if (ret == -1) {
> 		perror("PTRACE_ATTACH");
> 		exit(1);
> 	}
> 	ret = waitpid(pid, &status, 0);
> 	if (ret == -1) {
> 		perror("waitpid (2)");
> 		exit(1);
> 	}
> 	ret = ptrace(PTRACE_KILL, pid, NULL, NULL);
> 	if (ret == -1) {
> 		perror("PTRACE_KILL");
> 		exit(1);
> 	}
>
> 	return 0;
> }
>
> Test result:
>
>     hirofumi@devron (ptrace)[1111]$ ps ax|grep ptrace
>       688 tty1     S      0:00 grep ptrace
>     hirofumi@devron (ptrace)[1112]$ ls
>     ptrace  ptrace.c
>     hirofumi@devron (ptrace)[1113]$ ./ptrace
>     hirofumi@devron (ptrace)[1114]$ ps ax|grep ptrace
>       691 tty1     R      0:04 ./ptrace
>       693 tty1     S      0:00 grep ptrace
>     hirofumi@devron (ptrace)[1115]$
>
> Do I misunderstand something?
> -- 
> OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>