[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 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -213,6 +213,16 @@ static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
        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 *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
        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 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
                        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 @@ Enomem:
  *
  *  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 @@ Enomem:
  * (*)   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 @@ static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
 
        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 @@ static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
        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 @@ static int do_move_mount(struct nameidata *nd, char *old_name)
         */
        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 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
                                    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 @@ int copy_namespace(int flags, struct task_struct *tsk)
        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 (file)
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -82,6 +82,8 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
        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 (file)
--- 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 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -104,6 +104,7 @@ extern int dir_notify_enable;
 #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 (file)
--- 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 {