[PATCH] setpgid: should not accept ptraced childs

sys_setpgid() allows to change ->pgrp of ptraced childs.

'man setpgid' does not tell anything about that, so I consider
this behaviour is a bug.
Signed-off-by: NOleg Nesterov <oleg@tv-sign.ru>
Cc: Oren Laadan <orenl@cs.columbia.edu>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/sys.c

@@ -1114,7 +1114,7 @@ asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
 	if (!thread_group_leader(p))
 		goto out;
 
-	if (p->parent == current || p->real_parent == group_leader) {
+	if (p->real_parent == group_leader) {
 		err = -EPERM;
 		if (p->signal->session != group_leader->signal->session)
 			goto out;