From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49952 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732299AbeGJWnD (ORCPT ); Tue, 10 Jul 2018 18:43:03 -0400 Subject: [PATCH 03/32] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #9] From: David Howells To: viro@zeniv.linux.org.uk Cc: dhowells@redhat.com, linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Date: Tue, 10 Jul 2018 23:41:48 +0100 Message-ID: <153126250894.14533.11701155170173292521.stgit@warthog.procyon.org.uk> In-Reply-To: <153126248868.14533.9751473662727327569.stgit@warthog.procyon.org.uk> References: <153126248868.14533.9751473662727327569.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: From: Al Viro Allow a detached tree created by open_tree(..., OPEN_TREE_CLONE) to be attached by move_mount(2). If by the time of final fput() of OPEN_TREE_CLONE-opened file its tree is not detached anymore, it won't be dissolved. move_mount(2) is adjusted to handle detached source. That gives us equivalents of mount --bind and mount --rbind. Signed-off-by: Al Viro --- fs/namespace.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index e95b2bc8fcfe..bd2526b24afb 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1845,8 +1845,10 @@ void dissolve_on_fput(struct vfsmount *mnt) { namespace_lock(); lock_mount_hash(); - mntget(mnt); - umount_tree(real_mount(mnt), UMOUNT_SYNC); + if (!real_mount(mnt)->mnt_ns) { + mntget(mnt); + umount_tree(real_mount(mnt), UMOUNT_SYNC); + } unlock_mount_hash(); namespace_unlock(); } @@ -2453,6 +2455,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) struct mount *old; struct mountpoint *mp; int err; + bool attached; mp = lock_mount(new_path); err = PTR_ERR(mp); @@ -2463,10 +2466,19 @@ static int do_move_mount(struct path *old_path, struct path *new_path) p = real_mount(new_path->mnt); err = -EINVAL; - if (!check_mnt(p) || !check_mnt(old)) + /* The mountpoint must be in our namespace. */ + if (!check_mnt(p)) + goto out1; + /* The thing moved should be either ours or completely unattached. */ + if (old->mnt_ns && !check_mnt(old)) goto out1; - if (!mnt_has_parent(old)) + attached = mnt_has_parent(old); + /* + * We need to allow open_tree(OPEN_TREE_CLONE) followed by + * move_mount(), but mustn't allow "/" to be moved. + */ + if (old->mnt_ns && !attached) goto out1; if (old->mnt.mnt_flags & MNT_LOCKED) @@ -2481,7 +2493,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) /* * Don't move a mount residing in a shared parent. */ - if (IS_MNT_SHARED(old->mnt_parent)) + if (attached && IS_MNT_SHARED(old->mnt_parent)) goto out1; /* * Don't move a mount tree containing unbindable mounts to a destination @@ -2495,7 +2507,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) goto out1; err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp, - &parent_path); + attached ? &parent_path : NULL); if (err) goto out1; @@ -3179,6 +3191,8 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, /* * Move a mount from one place to another. + * In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be + * used to copy a mount subtree. * * Note the flags value is a combination of MOVE_MOUNT_* flags. */