[PATCH] Missing mnt_namespace update in copy_namespace()

copy_namespace() forgets to switch the new 'mnt_namespace' field in the
vfsmounts of the new namespace.

fs/namespace.c

@@ -1037,6 +1037,7 @@ int copy_namespace(int flags, struct task_struct *tsk)
 	struct namespace *new_ns;
 	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
 	struct fs_struct *fs = tsk->fs;
+	struct vfsmount *p, *q;
 
 	if (!namespace)
 		return 0;
@@ -1071,14 +1072,16 @@ int copy_namespace(int flags, struct task_struct *tsk)
 	list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
 	spin_unlock(&vfsmount_lock);
 
-	/* Second pass: switch the tsk->fs->* elements */
-	if (fs) {
-		struct vfsmount *p, *q;
-		write_lock(&fs->lock);
-
+	/*
+	 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
+	 * as belonging to new namespace.  We have already acquired a private
+	 * fs_struct, so tsk->fs->lock is not needed.
+	 */
 	p = namespace->root;
 	q = new_ns->root;
 	while (p) {
+		q->mnt_namespace = new_ns;
+		if (fs) {
 			if (p == fs->rootmnt) {
 				rootmnt = p;
 				fs->rootmnt = mntget(q);
@@ -1091,11 +1094,10 @@ int copy_namespace(int flags, struct task_struct *tsk)
 				altrootmnt = p;
 				fs->altrootmnt = mntget(q);
 			}
+		}
 		p = next_mnt(p, namespace->root);
 		q = next_mnt(q, new_ns->root);
 	}
-		write_unlock(&fs->lock);
-	}
 	up_write(&tsk->namespace->sem);
 
 	tsk->namespace = new_ns;