mqueue: Explicitly capture the user namespace to send the notification to.

Stop relying on user->user_ns which is going away and instead capture
the user_namespace of the process we are supposed to notify.
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

ipc/mqueue.c

@@ -66,6 +66,7 @@ struct mqueue_inode_info {
 
 	struct sigevent notify;
 	struct pid* notify_owner;
+	struct user_namespace *notify_user_ns;
 	struct user_struct *user;	/* user who created, for accounting */
 	struct sock *notify_sock;
 	struct sk_buff *notify_cookie;
@@ -139,6 +140,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		INIT_LIST_HEAD(&info->e_wait_q[0].list);
 		INIT_LIST_HEAD(&info->e_wait_q[1].list);
 		info->notify_owner = NULL;
+		info->notify_user_ns = NULL;
 		info->qsize = 0;
 		info->user = NULL;	/* set when all is ok */
 		memset(&info->attr, 0, sizeof(info->attr));
@@ -536,7 +538,7 @@ static void __do_notify(struct mqueue_inode_info *info)
 			rcu_read_lock();
 			sig_i.si_pid = task_tgid_nr_ns(current,
 						ns_of_pid(info->notify_owner));
-			sig_i.si_uid = user_ns_map_uid(info->user->user_ns,
+			sig_i.si_uid = user_ns_map_uid(info->notify_user_ns,
 						current_cred(), current_uid());
 			rcu_read_unlock();
 
@@ -550,7 +552,9 @@ static void __do_notify(struct mqueue_inode_info *info)
 		}
 		/* after notification unregisters process */
 		put_pid(info->notify_owner);
+		put_user_ns(info->notify_user_ns);
 		info->notify_owner = NULL;
+		info->notify_user_ns = NULL;
 	}
 	wake_up(&info->wait_q);
 }
@@ -575,7 +579,9 @@ static void remove_notification(struct mqueue_inode_info *info)
 		netlink_sendskb(info->notify_sock, info->notify_cookie);
 	}
 	put_pid(info->notify_owner);
+	put_user_ns(info->notify_user_ns);
 	info->notify_owner = NULL;
+	info->notify_user_ns = NULL;
 }
 
 static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
@@ -1140,6 +1146,7 @@ SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
 		}
 
 		info->notify_owner = get_pid(task_tgid(current));
+		info->notify_user_ns = get_user_ns(current_user_ns());
 		inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	}
 	spin_unlock(&info->lock);