Re: [RFC PATCH 08/27] containers, vfs: Honour CONTAINER_NEW_EMPTY_FS_NS

On Fri, Feb 15, 2019 at 04:08:29PM +0000, David Howells wrote:

+	mnt_ns = alloc_mnt_ns(container->cred->user_ns, false);
+	if (IS_ERR(mnt_ns)) {
+		ret = PTR_ERR(mnt_ns);
+		goto out_fd;
+	}
+
+	mnt = real_mount(path->mnt);
+	mnt_add_count(mnt, 1);
+	mnt->mnt_ns = mnt_ns;
+	mnt_ns->root = mnt;
+	mnt_ns->mounts++;
+	list_add(&mnt->mnt_list, &mnt_ns->list);
+
+	ret = -EBUSY;
+	spin_lock(&container->lock);
+	if (!container->ns->mnt_ns) {
+		container->ns->mnt_ns = mnt_ns;
+		write_seqcount_begin(&container->seq);
+		container->root.mnt = path->mnt;
+		container->root.dentry = path->dentry;
+		write_seqcount_end(&container->seq);
+		path_get(&container->root);
+		mnt_ns = NULL;
+		ret = 0;
+	}

Almost certainly buggered.  Assumptions that we _won't_ get
to absolute root of namespace (it's overmounted and we are
chrooted into it, basically) had been made in quite a few
places.  The thing you are creating is *not* like normal
namespaces in that respect.