4 files changed, 20 insertions, 4 deletions

diff --git a/include/linux/pid.h b/include/linux/pid.h
index b152d44fb181..2381c973d897 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -121,6 +121,7 @@ int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
 
 extern struct pid *alloc_pid(struct pid_namespace *ns);
 extern void free_pid(struct pid *pid);
+extern void disable_pid_allocation(struct pid_namespace *ns);
 
 /*
  * ns_of_pid() returns the pid namespace in which the specified pid was
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index bf285999273a..215e5e3dda10 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -21,7 +21,7 @@ struct pid_namespace {
         struct kref kref;
         struct pidmap pidmap[PIDMAP_ENTRIES];
         int last_pid;
-        int nr_hashed;
+        unsigned int nr_hashed;
         struct task_struct *child_reaper;
         struct kmem_cache *pid_cachep;
         unsigned int level;
@@ -42,6 +42,8 @@ struct pid_namespace {
 
 extern struct pid_namespace init_pid_ns;
 
+#define PIDNS_HASH_ADDING (1U << 31)
+
 #ifdef CONFIG_PID_NS
 static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
 {
diff --git a/kernel/pid.c b/kernel/pid.c
index 36aa02ff17d6..de9af600006f 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -270,7 +270,6 @@ void free_pid(struct pid *pid)
                         wake_up_process(ns->child_reaper);
                         break;
                 case 0:
-                        ns->nr_hashed = -1;
                         schedule_work(&ns->proc_work);
                         break;
                 }
@@ -319,7 +318,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 
         upid = pid->numbers + ns->level;
         spin_lock_irq(&pidmap_lock);
-        if (ns->nr_hashed < 0)
+        if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
                 goto out_unlock;
         for ( ; upid >= pid->numbers; --upid) {
                 hlist_add_head_rcu(&upid->pid_chain,
@@ -342,6 +341,13 @@ out_free:
         goto out;
 }
 
+void disable_pid_allocation(struct pid_namespace *ns)
+{
+        spin_lock_irq(&pidmap_lock);
+        ns->nr_hashed &= ~PIDNS_HASH_ADDING;
+        spin_unlock_irq(&pidmap_lock);
+}
+
 struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
 {
         struct hlist_node *elem;
@@ -573,6 +579,9 @@ void __init pidhash_init(void)
 
 void __init pidmap_init(void)
 {
+        /* Veryify no one has done anything silly */
+        BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
+
         /* bump default and minimum pid_max based on number of cpus */
         pid_max = min(pid_max_max, max_t(int, pid_max,
                                 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
@@ -584,7 +593,7 @@ void __init pidmap_init(void)
         /* Reserve PID 0. We never call free_pidmap(0) */
         set_bit(0, init_pid_ns.pidmap[0].page);
         atomic_dec(&init_pid_ns.pidmap[0].nr_free);
-        init_pid_ns.nr_hashed = 1;
+        init_pid_ns.nr_hashed = PIDNS_HASH_ADDING;
 
         init_pid_ns.pid_cachep = KMEM_CACHE(pid,
                         SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index fdbd0cdf271a..c1c3dc1c6023 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -115,6 +115,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
         ns->level = level;
         ns->parent = get_pid_ns(parent_pid_ns);
         ns->user_ns = get_user_ns(user_ns);
+        ns->nr_hashed = PIDNS_HASH_ADDING;
         INIT_WORK(&ns->proc_work, proc_cleanup_work);
 
         set_bit(0, ns->pidmap[0].page);
@@ -181,6 +182,9 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
         int rc;
         struct task_struct *task, *me = current;
 
+        /* Don't allow any more processes into the pid namespace */
+        disable_pid_allocation(pid_ns);
+
         /* Ignore SIGCHLD causing any terminated children to autoreap */
         spin_lock_irq(&me->sighand->siglock);
         me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;