vfs: more mnt_parent cleanups

[linux-3.10.git] / fs / namespace.c

diff --git a/fs/namespace.c b/fs/namespace.c
index ec8512478b04fff1697bd9fb058176f5e67b4144..7aad258dcaf6db9600d3dcf187ce8493baf60e8e 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1876,8 +1876,7 @@ static int do_move_mount(struct path *path, char *old_name)
        /*
         * Don't move a mount residing in a shared parent.
         */
-       if (old_path.mnt->mnt_parent &&
-           IS_MNT_SHARED(old_path.mnt->mnt_parent))
+       if (IS_MNT_SHARED(old_path.mnt->mnt_parent))
                goto out1;
        /*
         * Don't move a mount tree containing unbindable mounts to a destination
@@ -2533,6 +2532,31 @@ out_type:
        return ret;
 }
 
+/*
+ * Return true if path is reachable from root
+ *
+ * namespace_sem or vfsmount_lock is held
+ */
+bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
+                        const struct path *root)
+{
+       while (mnt != root->mnt && mnt_has_parent(mnt)) {
+               dentry = mnt->mnt_mountpoint;
+               mnt = mnt->mnt_parent;
+       }
+       return mnt == root->mnt && is_subdir(dentry, root->dentry);
+}
+
+int path_is_under(struct path *path1, struct path *path2)
+{
+       int res;
+       br_read_lock(vfsmount_lock);
+       res = is_path_reachable(path1->mnt, path1->dentry, path2);
+       br_read_unlock(vfsmount_lock);
+       return res;
+}
+EXPORT_SYMBOL(path_is_under);
+
 /*
  * pivot_root Semantics:
  * Moves the root file system of the current process to the directory put_old,
@@ -2561,7 +2585,6 @@ out_type:
 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                const char __user *, put_old)
 {
-       struct vfsmount *tmp;
        struct path new, old, parent_path, root_parent, root;
        int error;
 
@@ -2611,18 +2634,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
        if (!mnt_has_parent(new.mnt))
                goto out4; /* not attached */
        /* make sure we can reach put_old from new_root */
-       tmp = old.mnt;
-       if (tmp != new.mnt) {
-               for (;;) {
-                       if (!mnt_has_parent(tmp))
-                               goto out4; /* already mounted on put_old */
-                       if (tmp->mnt_parent == new.mnt)
-                               break;
-                       tmp = tmp->mnt_parent;
-               }
-               if (!is_subdir(tmp->mnt_mountpoint, new.dentry))
-                       goto out4;
-       } else if (!is_subdir(old.dentry, new.dentry))
+       if (!is_path_reachable(old.mnt, old.dentry, &new))
                goto out4;
        br_write_lock(vfsmount_lock);
        detach_mnt(new.mnt, &parent_path);