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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12] From: David Howells To: viro@zeniv.linux.org.uk Cc: torvalds@linux-foundation.org, dhowells@redhat.com, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com Date: Fri, 21 Sep 2018 17:30:34 +0100 Message-ID: <153754743491.17872.12115848333103740766.stgit@warthog.procyon.org.uk> In-Reply-To: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> References: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.25 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Fri, 21 Sep 2018 16:30:37 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Signed-off-by: David Howells --- fs/namespace.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index dd38141b1723..caf5c55ef555 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1785,8 +1785,10 @@ void dissolve_on_fput(struct vfsmount *mnt) { namespace_lock(); lock_mount_hash(); - mntget(mnt); - umount_tree(real_mount(mnt), UMOUNT_CONNECTED); + if (!real_mount(mnt)->mnt_ns) { + mntget(mnt); + umount_tree(real_mount(mnt), UMOUNT_CONNECTED); + } unlock_mount_hash(); namespace_unlock(); } @@ -2393,6 +2395,7 @@ 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); @@ -2403,10 +2406,19 @@ 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) @@ -2421,7 +2433,7 @@ 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 @@ -2435,7 +2447,7 @@ 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; @@ -3121,6 +3133,8 @@ 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. */