[PATCH] unbindable mounts
An unbindable mount does not forward or receive propagation. Also
unbindable mount disallows bind mounts. The semantics is as follows.
Bind semantics:
It is invalid to bind mount an unbindable mount.
Move semantics:
It is invalid to move an unbindable mount under shared mount.
Clone-namespace semantics:
If a mount is unbindable in the parent namespace, the corresponding
cloned mount in the child namespace becomes unbindable too. Note:
there is subtle difference, unbindable mounts cannot be bind mounted
but can be cloned during clone-namespace.
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/namespace.c b/fs/namespace.c
index 0896703..caa9187 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -213,6 +213,16 @@
return list_entry(next, struct vfsmount, mnt_child);
}
+static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
+{
+ struct list_head *prev = p->mnt_mounts.prev;
+ while (prev != &p->mnt_mounts) {
+ p = list_entry(prev, struct vfsmount, mnt_child);
+ prev = p->mnt_mounts.prev;
+ }
+ return p;
+}
+
static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
int flag)
{
@@ -650,6 +660,9 @@
struct vfsmount *res, *p, *q, *r, *s;
struct nameidata nd;
+ if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
+ return NULL;
+
res = q = clone_mnt(mnt, dentry, flag);
if (!q)
goto Enomem;
@@ -661,6 +674,10 @@
continue;
for (s = r; s; s = next_mnt(s, r)) {
+ if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
+ s = skip_mnt_tree(s);
+ continue;
+ }
while (p != s->mnt_parent) {
p = p->mnt_parent;
q = q->mnt_parent;
@@ -698,18 +715,18 @@
*
* NOTE: in the table below explains the semantics when a source mount
* of a given type is attached to a destination mount of a given type.
- * -------------------------------------------------------------
- * | BIND MOUNT OPERATION |
- * |*************************************************************
- * | source-->| shared | private | slave |
- * | dest | | | |
- * | | | | | |
- * | v | | | |
- * |*************************************************************
- * | shared | shared (++) | shared (+) | shared(+++)|
- * | | | | |
- * |non-shared| shared (+) | private | slave (*) |
- * **************************************************************
+ * ---------------------------------------------------------------------------
+ * | BIND MOUNT OPERATION |
+ * |**************************************************************************
+ * | source-->| shared | private | slave | unbindable |
+ * | dest | | | | |
+ * | | | | | | |
+ * | v | | | | |
+ * |**************************************************************************
+ * | shared | shared (++) | shared (+) | shared(+++)| invalid |
+ * | | | | | |
+ * |non-shared| shared (+) | private | slave (*) | invalid |
+ * ***************************************************************************
* A bind operation clones the source mount and mounts the clone on the
* destination mount.
*
@@ -726,18 +743,18 @@
* (*) the cloned mount is made a slave of the same master as that of the
* source mount.
*
- * --------------------------------------------------------------
- * | MOVE MOUNT OPERATION |
- * |*************************************************************
- * | source-->| shared | private | slave |
- * | dest | | | |
- * | | | | | |
- * | v | | | |
- * |*************************************************************
- * | shared | shared (+) | shared (+) | shared(+++) |
- * | | | | |
- * |non-shared| shared (+*) | private | slave (*) |
- * **************************************************************
+ * ---------------------------------------------------------------------------
+ * | MOVE MOUNT OPERATION |
+ * |**************************************************************************
+ * | source-->| shared | private | slave | unbindable |
+ * | dest | | | | |
+ * | | | | | | |
+ * | v | | | | |
+ * |**************************************************************************
+ * | shared | shared (+) | shared (+) | shared(+++) | invalid |
+ * | | | | | |
+ * |non-shared| shared (+*) | private | slave (*) | unbindable |
+ * ***************************************************************************
*
* (+) the mount is moved to the destination. And is then propagated to
* all the mounts in the propagation tree of the destination mount.
@@ -854,6 +871,9 @@
down_write(&namespace_sem);
err = -EINVAL;
+ if (IS_MNT_UNBINDABLE(old_nd.mnt))
+ goto out;
+
if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
goto out;
@@ -911,6 +931,16 @@
return err;
}
+static inline int tree_contains_unbindable(struct vfsmount *mnt)
+{
+ struct vfsmount *p;
+ for (p = mnt; p; p = next_mnt(p, mnt)) {
+ if (IS_MNT_UNBINDABLE(p))
+ return 1;
+ }
+ return 0;
+}
+
static int do_move_mount(struct nameidata *nd, char *old_name)
{
struct nameidata old_nd, parent_nd;
@@ -954,6 +984,12 @@
*/
if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
goto out1;
+ /*
+ * Don't move a mount tree containing unbindable mounts to a destination
+ * mount which is shared.
+ */
+ if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
+ goto out1;
err = -ELOOP;
for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
if (p == old_nd.mnt)
@@ -1266,7 +1302,7 @@
data_page);
else if (flags & MS_BIND)
retval = do_loopback(&nd, dev_name, flags & MS_REC);
- else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE))
+ else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
retval = do_change_type(&nd, flags);
else if (flags & MS_MOVE)
retval = do_move_mount(&nd, dev_name);
@@ -1311,7 +1347,7 @@
down_write(&namespace_sem);
/* First pass: copy the tree topology */
new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root,
- CL_EXPIRE);
+ CL_COPY_ALL | CL_EXPIRE);
if (!new_ns->root) {
up_write(&namespace_sem);
kfree(new_ns);
diff --git a/fs/pnode.c b/fs/pnode.c
index 3e266c5..aeeec8b 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -82,6 +82,8 @@
if (type != MS_SLAVE) {
list_del_init(&mnt->mnt_slave);
mnt->mnt_master = NULL;
+ if (type == MS_UNBINDABLE)
+ mnt->mnt_flags |= MNT_UNBINDABLE;
}
}
diff --git a/fs/pnode.h b/fs/pnode.h
index b59f0e9..020e1bb 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -15,6 +15,7 @@
#define IS_MNT_SLAVE(mnt) (mnt->mnt_master)
#define IS_MNT_NEW(mnt) (!mnt->mnt_namespace)
#define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
+#define IS_MNT_UNBINDABLE(mnt) (mnt->mnt_flags & MNT_UNBINDABLE)
#define CL_EXPIRE 0x01
#define CL_SLAVE 0x02
diff --git a/include/linux/fs.h b/include/linux/fs.h
index eef66f5..1b5f502 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -104,6 +104,7 @@
#define MS_MOVE 8192
#define MS_REC 16384
#define MS_VERBOSE 32768
+#define MS_UNBINDABLE (1<<17) /* change to unbindable */
#define MS_PRIVATE (1<<18) /* change to private */
#define MS_SLAVE (1<<19) /* change to slave */
#define MS_SHARED (1<<20) /* change to shared */
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 7e133ae..dd4e83e 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -21,6 +21,7 @@
#define MNT_NODEV 0x02
#define MNT_NOEXEC 0x04
#define MNT_SHARED 0x10 /* if the vfsmount is a shared mount */
+#define MNT_UNBINDABLE 0x20 /* if the vfsmount is a unbindable mount */
#define MNT_PNODE_MASK 0x30 /* propogation flag mask */
struct vfsmount {