Ensure locks can not be created outside of the root file driver directory

Change-Id: I33870e03141b4a577415bbc7d625237b1d86b513

tooz/drivers/file.py

@@ -15,7 +15,6 @@
 # under the License.
 
 import logging
-import os
 import threading
 
 import fasteners
@@ -24,6 +23,7 @@ from oslo_utils import timeutils
 import tooz
 from tooz import coordination
 from tooz import locking
+from tooz import utils
 
 LOG = logging.getLogger(__name__)
 
@@ -89,7 +89,7 @@ class FileDriver(coordination.CoordinationDriver):
         self._lockdir = parsed_url.path
 
     def get_lock(self, name):
-        path = os.path.abspath(os.path.join(self._lockdir, name.decode()))
+        path = utils.safe_abs_path(self._lockdir, name.decode())
         return locking.SharedWeakLockHelper(self._lockdir, FileLock, path)
 
     @staticmethod

tooz/tests/test_utils.py

@@ -15,6 +15,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import os
+import tempfile
 
 import six
 from testtools import testcase
@@ -22,6 +24,24 @@ from testtools import testcase
 from tooz import utils
 
 
+class TestUtilsSafePath(testcase.TestCase):
+    base = tempfile.gettempdir()
+
+    def test_join(self):
+        self.assertEqual(os.path.join(self.base, 'b'),
+                         utils.safe_abs_path(self.base, "b"))
+        self.assertEqual(os.path.join(self.base, 'b', 'c'),
+                         utils.safe_abs_path(self.base, "b", 'c'))
+        self.assertEqual(self.base,
+                         utils.safe_abs_path(self.base, "b", 'c', '../..'))
+
+    def test_unsafe_join(self):
+        self.assertRaises(ValueError, utils.safe_abs_path,
+                          self.base, "../b")
+        self.assertRaises(ValueError, utils.safe_abs_path,
+                          self.base, "b", 'c', '../../../')
+
+
 class TestUtilsCollapse(testcase.TestCase):
 
     def test_bad_type(self):

tooz/utils.py

@@ -14,6 +14,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import os
+
 import msgpack
 from oslo_serialization import msgpackutils
 import six
@@ -21,6 +23,22 @@ import six
 from tooz import coordination
 
 
+def safe_abs_path(rooted_at, *pieces):
+    # Avoids the following junk...
+    #
+    # >>> import os
+    # >>> os.path.join("/b", "..")
+    # '/b/..'
+    # >>> os.path.abspath(os.path.join("/b", ".."))
+    # '/'
+    path = os.path.abspath(os.path.join(rooted_at, *pieces))
+    if not path.startswith(rooted_at):
+        raise ValueError("Unable to create path that is outside of"
+                         " parent directory '%s' using segments %s"
+                         % (rooted_at, list(pieces)))
+    return path
+
+
 def collapse(config, exclude=None, item_selector=None):
     """Collapses config with keys and **list/tuple** values.