X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/xvm-authz-locker.git/blobdiff_plain/7824b2db8f1795ea784d70def02c362d48ab91b5..5f5bda7c3b60eca33af5f9782a27832ca1c4eb37:/python/xvm/authz/locker.py

diff --git a/python/xvm/authz/locker.py b/python/xvm/authz/locker.py
new file mode 100644
index 0000000..59b480e
--- /dev/null
+++ b/python/xvm/authz/locker.py
@@ -0,0 +1,129 @@
+import errno
+
+from afs import acl
+from afs import fs
+from afs import pts
+
+from invirt import common
+from invirt.config import structs as config
+from invirt import remctl
+
+
+#
+# expandOwner and expandAdmin form the API that needs to be exported
+# for all authz modules.
+#
+
+
+def expandOwner(name):
+    """Expand an owner to a list of authorized users.
+
+    For the locker authz module, an owner is an Athena locker. Those
+    users who have been given the administrator ('a') bit on the root
+    of a locker are given access to any VM owned by that locker,
+    unless they also have been given a negative administrator bit.
+
+    If a locker doesn't exist, or we can't access the permissions, we
+    assume the ACL is empty.
+    """
+    try:
+        path = _lockerPath(name)
+        cell = fs.whichcell(path)
+        auth = _authenticate(cell)
+        a = acl.ACL.retrieve(path)
+
+        allowed = set()
+        for ent in a.pos:
+            if a.pos[ent] & acl.ADMINISTER:
+                allowed.update(_expandGroup(ent, cell=cell, auth=auth))
+        for ent in a.neg:
+            if a.neg[ent] & acl.ADMINISTER:
+                allowed.difference_update(_expandGroup(ent, cell=cell, auth=auth))
+
+        return allowed
+    except OSError, e:
+        if e.errno in (errno.ENOENT, errno.EACCES):
+            return []
+        else:
+            raise
+
+
+def expandAdmin(name):
+    """Expand an administrator to a list of authorized users.
+
+    For locker-based authorization, the administrator is always
+    interpreted as an AFS entry (either a user or a group) in the
+    machine's home cell (athena.mit.edu for XVM).
+    """
+    cell = config.authz.afs.cells[0].cell
+    auth = _authenticate(cell)
+    return _expandGroup(name, cell=cell, auth=auth)
+
+
+#
+# These are helper functions, and aren't part of the authz API
+#
+
+
+def _authenticate(cell):
+    """Acquire AFS tokens for a cell if encryption is required by config.
+
+    If the Invirt configuration requires connections to this cell to
+    be encrypted, acquires tokens and returns True. Otherwise, returns
+    False. Consumers of this function must still be sure to encrypt
+    their own connections if necessary.
+
+    Cells not listed in the Invirt configuration default to requiring
+    encryption in order to maintain security by default.
+
+    Due to AFS's cross-realm auto-PTS-creation mechanism, using
+    authenticated connections by default should only fail for cells
+    which authenticate directly against the machine's home realm and
+    cells distantly related to the machine's home realm.
+    """
+    for c in config.authz.afs.cells:
+        if c.cell == cell and not c.auth:
+            return False
+
+    remctl.checkKinit()
+    common.captureOutput(['aklog', '-c', cell])
+    return True
+
+
+def _expandGroup(name, cell=None, auth=False):
+    """Expand an AFS group into a list of its members.
+
+    Because groups are not global, but can vary from cell to cell,
+    this function accepts as an optional argument the cell in which
+    this group should be resolved.
+
+    If no cell is specified, it is assumed that the default cell (or
+    ThisCell) should be used.
+
+    If the name is a user, not a group, then a single-element set with
+    the same name is returned.
+
+    As with expandOwner, if a group doesn't exist or if we're unable
+    to retrieve its membership, we assume it's empty.
+    """
+    try:
+        ent = pts.PTS(cell, pts.PTS_ENCRYPT if auth else pts.PTS_UNAUTH).\
+            getEntry(name)
+        if ent.id > 0:
+            return set([ent.name])
+        else:
+            return set([x.name for x in ent.members])
+    except OSError, e:
+        if e.errno in (errno.ENOENT, errno.EACCESS):
+            return set()
+        else:
+            raise
+
+
+def _lockerPath(owner):
+    """Given the name of a locker, return a path to that locker.
+
+    This turns out to be pretty simple, thanks to the /mit
+    automounter.
+    """
+    return '/mit/%s' % owner