From c6c70f4455d1eda91065e93cc4f7eddf4499b105 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 30 Jan 2017 19:17:35 +0100 Subject: [PATCH] exit: fix the setns() && PR_SET_CHILD_SUBREAPER interaction 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 Signed-off-by: Eric W. Biederman --- kernel/exit.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 8f14b866f9f6..5cfbd595f918 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -578,15 +578,18 @@ 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) -- 2.30.2