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authorEric W. Biederman <ebiederm@xmission.com>2006-04-14 06:05:55 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-04-14 11:49:19 -0400
commitc06511d12d720b23c8dffff23004f0a888698f20 (patch)
tree96916946cd8374821b10316c8f5fabc4917a38d6 /fs
parent0e5e24bf64b755a034d8294303bc61d8f40ebeaf (diff)
[PATCH] de_thread: Don't change our parents and ptrace flags.
This is two distinct changes. - Not changing our real parents. - Not changing our ptrace parents. Not changing our real parents is trivially correct because both tasks have the same real parents as they are part of a thread group. Now that we demote the leader to a thread there is no longer any reason to change it's parentage. Not changing our ptrace parents is a user visible change if someone looks hard enough. I don't think user space applications will care or even notice. In the practical and I think common case a debugger will have attached to all of the threads using the same ptrace flags. From my quick skim of strace and gdb that appears to be the case. Which if true means debuggers will not notice a change. Before this point we have already generated a ptrace event in do_exit that reports the leaders pid has died so de_thread is visible to a debugger. Which means attempting to hide this case by copying flags around appears excessive. By not doing anything it avoids all of the weird locking issues between de_thread and ptrace attach, and removes one case from consideration for fixing the ptrace locking. This only addresses Oleg's first concern with ptrace_attach, that of the problems caused by reparenting. Oleg's second concern is essentially a race between ptrace_attach and release_task that causes an oops when we get to force_sig_specific. There is nothing special about de_thread with respect to that race. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c27
1 files changed, 0 insertions, 27 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 3234a0c32d54..4121bb559739 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -665,9 +665,7 @@ static int de_thread(struct task_struct *tsk)
665 * and to assume its PID: 665 * and to assume its PID:
666 */ 666 */
667 if (!thread_group_leader(current)) { 667 if (!thread_group_leader(current)) {
668 struct task_struct *parent;
669 struct dentry *proc_dentry1, *proc_dentry2; 668 struct dentry *proc_dentry1, *proc_dentry2;
670 unsigned long ptrace;
671 669
672 /* 670 /*
673 * Wait for the thread group leader to be a zombie. 671 * Wait for the thread group leader to be a zombie.
@@ -704,22 +702,6 @@ static int de_thread(struct task_struct *tsk)
704 * two threads with a switched PID, and release 702 * two threads with a switched PID, and release
705 * the former thread group leader: 703 * the former thread group leader:
706 */ 704 */
707 ptrace = leader->ptrace;
708 parent = leader->parent;
709 if (unlikely(ptrace) && unlikely(parent == current)) {
710 /*
711 * Joker was ptracing his own group leader,
712 * and now he wants to be his own parent!
713 * We can't have that.
714 */
715 ptrace = 0;
716 }
717
718 ptrace_unlink(current);
719 ptrace_unlink(leader);
720 remove_parent(current);
721 remove_parent(leader);
722
723 705
724 /* Become a process group leader with the old leader's pid. 706 /* Become a process group leader with the old leader's pid.
725 * Note: The old leader also uses thispid until release_task 707 * Note: The old leader also uses thispid until release_task
@@ -732,8 +714,6 @@ static int de_thread(struct task_struct *tsk)
732 attach_pid(current, PIDTYPE_SID, current->signal->session); 714 attach_pid(current, PIDTYPE_SID, current->signal->session);
733 list_add_tail(&current->tasks, &init_task.tasks); 715 list_add_tail(&current->tasks, &init_task.tasks);
734 716
735 current->parent = current->real_parent = leader->real_parent;
736 leader->parent = leader->real_parent = child_reaper;
737 current->group_leader = current; 717 current->group_leader = current;
738 leader->group_leader = current; 718 leader->group_leader = current;
739 719
@@ -742,13 +722,6 @@ static int de_thread(struct task_struct *tsk)
742 detach_pid(leader, PIDTYPE_SID); 722 detach_pid(leader, PIDTYPE_SID);
743 list_del_init(&leader->tasks); 723 list_del_init(&leader->tasks);
744 724
745 add_parent(current);
746 add_parent(leader);
747 if (ptrace) {
748 current->ptrace = ptrace;
749 __ptrace_link(current, parent);
750 }
751
752 current->exit_signal = SIGCHLD; 725 current->exit_signal = SIGCHLD;
753 726
754 BUG_ON(leader->exit_state != EXIT_ZOMBIE); 727 BUG_ON(leader->exit_state != EXIT_ZOMBIE);