From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752773AbeCWXPS (ORCPT ); Fri, 23 Mar 2018 19:15:18 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:51646 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752163AbeCWXPQ (ORCPT ); Fri, 23 Mar 2018 19:15:16 -0400 Date: Fri, 23 Mar 2018 23:15:11 +0000 From: Al Viro To: "Eric W. Biederman" Cc: Aleksa Sarai , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org Subject: Re: [PATCH 1/2] fs: Extend mount_ns with support for a fast namespace to vfsmount function Message-ID: <20180323231511.GK30522@ZenIV.linux.org.uk> References: <20180323060457.sxgsd3j2obi33fyw@gordon> <87k1u3ti9e.fsf@xmission.com> <87fu4qo4ff.fsf_-_@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fu4qo4ff.fsf_-_@xmission.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 23, 2018 at 04:41:40PM -0500, Eric W. Biederman wrote: > struct dentry *mount_ns(struct file_system_type *fs_type, > int flags, void *data, void *ns, struct user_namespace *user_ns, > + struct vfsmount *(*ns_to_mnt)(void *ns), > int (*fill_super)(struct super_block *, void *, int)) > { > struct super_block *sb; > - > + int (*test_super)(struct super_block *, void *) = ns_test_super; > /* Don't allow mounting unless the caller has CAP_SYS_ADMIN > * over the namespace. > */ > if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN)) > return ERR_PTR(-EPERM); > > - sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags, > - user_ns, ns); > + if (ns_to_mnt) { > + test_super = NULL; > + if (!(flags & SB_KERNMOUNT)) { > + struct vfsmount *m = ns_to_mnt(ns); > + if (IS_ERR(m)) > + return ERR_CAST(m); > + atomic_inc(&m->mnt_sb->s_active); > + down_write(&m->mnt_sb->s_umount); > + return dget(m->mnt_root); This is completely wrong. Look: * SB_KERNMOUNT and !SB_KERNMOUNT cases are almost entirely isolated; completely so once that ns_to_mnt becomes unconditionally non-NULL. * in !SB_KERNMOUNT passing ns_to_mnt() is pointless - you might as well pass existing vfsmount (or ERR_PTR()) and use _that_. fill_super() is not used at all in that case. * is SB_KERNMOUNT ns_to_mnt serves only as a flag, eventually constant true. So let's split it in two helpers and give them sane arguments.