| From | David Howells <> | Subject | [PATCH 37/73] union-mount: Prevent topmost file system from being mounted elsewhere [ver #2] | Date | Tue, 21 Feb 2012 18:02:09 +0000 |
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From: Valerie Aurora <vaurora@redhat.com>
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.
Original-author: Valerie Aurora <vaurora@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> ---
fs/namespace.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c index aa6b1ef..3c950fa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2091,6 +2091,11 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags) if (S_ISLNK(newmnt->mnt.mnt_root->d_inode->i_mode)) goto unlock; + /* Top layers of union mounts can't be mounted elsewhere */ + err = -EBUSY; + if (newmnt->mnt.mnt_sb->s_union_lower_mnts) + goto unlock; + newmnt->mnt.mnt_flags = mnt_flags; err = graft_tree(newmnt, path);
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