reparent_thread: fix a zombie leak if /sbin/init ignores SIGCHLD
If /sbin/init ignores SIGCHLD and we re-parent a zombie, it is leaked.
reparent_thread() does do_notify_parent() which sets ->exit_signal = -1 in
this case. This means that nobody except us can reap it, the detached
task is not visible to do_wait().
Change reparent_thread() to return a boolean (like __pthread_detach) to
indicate that the thread is dead and must be released. Also change
forget_original_parent() to add the child to ptrace_dead list in this
case.
The naming becomes insane, the next patch does the cleanup.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/exit.c b/kernel/exit.c
index 5be0a40..3e09b7c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -810,8 +810,11 @@
}
}
-static void reparent_thread(struct task_struct *p, struct task_struct *father)
+/* Returns nonzero if the child should be released. */
+static int reparent_thread(struct task_struct *p, struct task_struct *father)
{
+ int dead;
+
if (p->pdeath_signal)
/* We already hold the tasklist_lock here. */
group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
@@ -819,12 +822,12 @@
list_move_tail(&p->sibling, &p->real_parent->children);
if (task_detached(p))
- return;
+ return 0;
/* If this is a threaded reparent there is no need to
* notify anyone anything has happened.
*/
if (same_thread_group(p->real_parent, father))
- return;
+ return 0;
/* We don't want people slaying init. */
p->exit_signal = SIGCHLD;
@@ -832,11 +835,19 @@
/* If we'd notified the old parent about this child's death,
* also notify the new parent.
*/
+ dead = 0;
if (!p->ptrace &&
- p->exit_state == EXIT_ZOMBIE && thread_group_empty(p))
+ p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
do_notify_parent(p, p->exit_signal);
+ if (task_detached(p)) {
+ p->exit_state = EXIT_DEAD;
+ dead = 1;
+ }
+ }
kill_orphaned_pgrp(p, father);
+
+ return dead;
}
/*
@@ -896,7 +907,8 @@
BUG_ON(p->ptrace);
p->parent = p->real_parent;
}
- reparent_thread(p, father);
+ if (reparent_thread(p, father))
+ list_add(&p->ptrace_entry, &ptrace_dead);;
}
write_unlock_irq(&tasklist_lock);