| Message ID | 153313706468.13253.16771852721230651938.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | VFS: Introduce filesystem context [ver #11] | expand |
On 01/08/2018 16:24, David Howells wrote: > From: Al Viro<viro@zeniv.linux.org.uk> > > 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<viro@zeniv.linux.org.uk> > Signed-off-by: David Howells<dhowells@redhat.com> > --- > > fs/namespace.c | 26 ++++++++++++++++++++------ > 1 file changed, 20 insertions(+), 6 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index e2934a4f342b..3981fd7b13f5 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2464,10 +2467,19 @@ 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; Technically, I think the comment should say "mustn't allow rootfs to be moved". "rootfs", as in Documentation/filesystems/ramfs-rootfs-initramfs.txt. Moving "/" is allowed. # unshare -m # cd /mnt # mount -ttmpfs none / # mount --move --no-canonicalize /.. /mnt # (Or if you want to quibble about "/.." v.s. "/" - # unshare -m # cd /mnt # mount --rbind / / # chroot --skip-chdir /.. # mount --move --no-canonicalize / .
diff --git a/fs/namespace.c b/fs/namespace.c index e2934a4f342b..3981fd7b13f5 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1846,8 +1846,10 @@ 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(); } @@ -2454,6 +2456,7 @@ 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); @@ -2464,10 +2467,19 @@ 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) @@ -2482,7 +2494,7 @@ 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 @@ -2496,7 +2508,7 @@ 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; @@ -3182,6 +3194,8 @@ 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. */