[PATCH] kill an obsolete sub-thread-ptrace stuff

[PATCH] kill an obsolete sub-thread-ptrace stuff

[Oleg Nesterov]

There is a couple of subtle checks which were needed to handle ptracing from
the same thread group. This was deprecated a long ago, imho this code just
complicates the understanding.

And, the "->parent->signal->flags & SIGNAL_GROUP_EXIT" check in exit_notify()
is not right. SIGNAL_GROUP_EXIT can mean exec(), not exit_group(). This means
ptracer can lose a ptraced zombie on exec(). Minor problem, but still the bug.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- t/kernel/exit.c~PT_TG	2007-08-03 18:05:52.000000000 +0400
+++ t/kernel/exit.c	2007-08-03 21:10:40.000000000 +0400
@@ -802,7 +802,7 @@ static void exit_notify(struct task_stru
 		__kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
 	}
 
-	/* Let father know we died 
+	/* Let father know we died
 	 *
 	 * Thread signals are configurable, but you aren't going to use
 	 * that to send signals to arbitary processes. 
@@ -815,9 +815,7 @@ static void exit_notify(struct task_stru
 	 * If our self_exec id doesn't match our parent_exec_id then
 	 * we have changed execution domain as these two values started
 	 * the same after a fork.
-	 *	
 	 */
-	
 	if (tsk->exit_signal != SIGCHLD && tsk->exit_signal != -1 &&
 	    ( tsk->parent_exec_id != t->self_exec_id  ||
 	      tsk->self_exec_id != tsk->parent_exec_id)
@@ -837,9 +835,7 @@ static void exit_notify(struct task_stru
 	}
 
 	state = EXIT_ZOMBIE;
-	if (tsk->exit_signal == -1 &&
-	    (likely(tsk->ptrace == 0) ||
-	     unlikely(tsk->parent->signal->flags & SIGNAL_GROUP_EXIT)))
+	if (tsk->exit_signal == -1 && likely(!tsk->ptrace))
 		state = EXIT_DEAD;
 	tsk->exit_state = state;
 
--- t/kernel/signal.c~PT_TG	2007-07-28 16:58:17.000000000 +0400
+++ t/kernel/signal.c	2007-08-03 21:11:59.000000000 +0400
@@ -1561,10 +1561,6 @@ static inline int may_ptrace_stop(void)
 		    (current->ptrace & PT_ATTACHED)))
 		return 0;
 
-	if (unlikely(current->signal == current->parent->signal) &&
-	    unlikely(current->signal->flags & SIGNAL_GROUP_EXIT))
-		return 0;
-
 	/*
 	 * Are we in the middle of do_coredump?
 	 * If so and our tracer is also part of the coredump stopping

Re: [PATCH] kill an obsolete sub-thread-ptrace stuff

[Roland McGrath]

> There is a couple of subtle checks which were needed to handle ptracing from
> the same thread group. This was deprecated a long ago, imho this code just
> complicates the understanding.

Looks ok to me.

> And, the "->parent->signal->flags & SIGNAL_GROUP_EXIT" check in exit_notify()
> is not right. SIGNAL_GROUP_EXIT can mean exec(), not exit_group(). This means
> ptracer can lose a ptraced zombie on exec(). Minor problem, but still the bug.

This bug never happens because this check is only in the now-impossible
ptrace-same-group case.  The code can certainly go.


Thanks,
Roland

Re: [PATCH] kill an obsolete sub-thread-ptrace stuff

[Oleg Nesterov]

On 08/03, Roland McGrath wrote:
>
> > There is a couple of subtle checks which were needed to handle ptracing from
> > the same thread group. This was deprecated a long ago, imho this code just
> > complicates the understanding.
> 
> Looks ok to me.

Thanks!

> > And, the "->parent->signal->flags & SIGNAL_GROUP_EXIT" check in exit_notify()
> > is not right. SIGNAL_GROUP_EXIT can mean exec(), not exit_group(). This means
> > ptracer can lose a ptraced zombie on exec(). Minor problem, but still the bug.
> 
> This bug never happens because this check is only in the now-impossible
> ptrace-same-group case.

This means that changelog is wrong and should be changed.

However, I disagree. exit_notify() doesn't check the ptrace-same-group case. So,
unless I missed something, we set EXIT_DEAD in any case, even if ptracer doesn't
belong to our thread group.

No?

Oleg.

Re: [PATCH] kill an obsolete sub-thread-ptrace stuff

[Roland McGrath]

> However, I disagree. exit_notify() doesn't check the ptrace-same-group
> case. So, unless I missed something, we set EXIT_DEAD in any case, even
> if ptracer doesn't belong to our thread group.

Oh, you're right.  I was reading the other line you changed.


Thanks,
Roland