find_new_reaper() checks same_thread_group(reaper, child_reaper) to
prevent the cross-namespace reparenting but this is not enough if the
exiting parent was injected by setns() + fork().
Suppose we have a process P in the root namespace and some namespace X.
P does setns() to enter the X namespace, and forks the child C.
C forks a grandchild G and exits.
The grandchild G should be re-parented to X->child_reaper, but in this
case the ->real_parent chain does not lead to ->child_reaper, so it will
be wrongly reparanted to P's sub-reaper or a global init.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/exit.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 76e263e..e8b0776 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -569,15 +569,18 @@ static struct task_struct *find_new_reaper(struct
task_struct *father,
return thread;
if (father->signal->has_child_subreaper) {
+ unsigned int ns_level = task_pid(father)->level;
/*
* Find the first ->is_child_subreaper ancestor in our pid_ns.
- * We start from father to ensure we can not look into another
- * namespace, this is safe because all its threads are dead.
+ * We can't check reaper != child_reaper to ensure we do not
+ * cross the namespaces, the exiting parent could be injected
+ * by setns() + fork().
+ * We check pid->level, this is slightly more efficient than
+ * task_active_pid_ns(reaper) != task_active_pid_ns(father).
*/
- for (reaper = father;
- !same_thread_group(reaper, child_reaper);
+ for (reaper = father->real_parent;
+ task_pid(reaper)->level == ns_level;
reaper = reaper->real_parent) {
- /* call_usermodehelper() descendants need this check */
if (reaper == &init_task)
break;
if (!reaper->signal->is_child_subreaper)
--
2.5.0
