1 files changed, 35 insertions, 4 deletions

diff --git a/ipc/namespace.c b/ipc/namespace.c
index 9171d948751e..4a5e752a9276 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -9,17 +9,26 @@
 #include <linux/rcupdate.h>
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
 
 #include "util.h"
 
 static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
 {
         struct ipc_namespace *ns;
+        int err;
 
         ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
         if (ns == NULL)
                 return ERR_PTR(-ENOMEM);
 
+        atomic_set(&ns->count, 1);
+        err = mq_init_ns(ns);
+        if (err) {
+                kfree(ns);
+                return ERR_PTR(err);
+        }
         atomic_inc(&nr_ipc_ns);
 
         sem_init_ns(ns);
@@ -34,7 +43,6 @@ static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
         ipcns_notify(IPCNS_CREATED);
         register_ipcns_notifier(ns);
 
-        kref_init(&ns->kref);
         return ns;
 }
 
@@ -84,11 +92,34 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
         up_write(&ids->rw_mutex);
 }
 
-void free_ipc_ns(struct kref *kref)
+/*
+ * put_ipc_ns - drop a reference to an ipc namespace.
+ * @ns: the namespace to put
+ *
+ * If this is the last task in the namespace exiting, and
+ * it is dropping the refcount to 0, then it can race with
+ * a task in another ipc namespace but in a mounts namespace
+ * which has this ipcns's mqueuefs mounted, doing some action
+ * with one of the mqueuefs files.  That can raise the refcount.
+ * So dropping the refcount, and raising the refcount when
+ * accessing it through the VFS, are protected with mq_lock.
+ *
+ * (Clearly, a task raising the refcount on its own ipc_ns
+ * needn't take mq_lock since it can't race with the last task
+ * in the ipcns exiting).
+ */
+void put_ipc_ns(struct ipc_namespace *ns)
 {
-        struct ipc_namespace *ns;
+        if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
+                mq_clear_sbinfo(ns);
+                spin_unlock(&mq_lock);
+                mq_put_mnt(ns);
+                free_ipc_ns(ns);
+        }
+}
 
-        ns = container_of(kref, struct ipc_namespace, kref);
+void free_ipc_ns(struct ipc_namespace *ns)
+{
         /*
          * Unregistering the hotplug notifier at the beginning guarantees
          * that the ipc namespace won't be freed while we are inside the