From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valerie Aurora Subject: [PATCH 23/34] union-mount: Prevent topmost file system from being mounted elsewhere Date: Thu, 16 Sep 2010 15:12:14 -0700 Message-ID: <1284675145-4391-24-git-send-email-vaurora@redhat.com> References: <1284675145-4391-1-git-send-email-vaurora@redhat.com> Cc: Miklos Szeredi , Christoph Hellwig , Andreas Gruenbacher , Nick Piggin , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Valerie Aurora To: Alexander Viro Return-path: In-Reply-To: <1284675145-4391-1-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org The device underlying the topmost read-write layer of a file system cannot be mounted anywhere else on the system. We keep a pointer to the union stack in the dentry of the topmost directory, so that dentry can't be part of a different mount, since dentries are shared between different mounts of the same device. Signed-off-by: Valerie Aurora --- fs/namespace.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 61256e6..26efaf3 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1998,6 +1998,11 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path, if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode)) goto unlock; + /* Top layers of union mounts can't be mounted elsewhere */ + err = -EBUSY; + if (newmnt->mnt_sb->s_union_lower_mnts) + goto unlock; + newmnt->mnt_flags = mnt_flags; if ((err = graft_tree(newmnt, path))) goto unlock; -- 1.6.3.3