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Description: Fix file existence disclosures (CVE-2020-16128)
Move set_euid_egid into aptdaemon.utils and use it when setting
Terminal and DebConfSocket properties, to ensure our checks only
have access to the same objects the user has.
.
Rewrite the checks so that they avoid extra os.access lookups and
have correct error handling for os.open() in the terminal, and
os.stat() in the debconf case.
Author: Julian Andres Klode <juliank@ubuntu.com>
Bug-Ubuntu: https://bugs.launchpad.net/bugs/1899513
--- a/aptdaemon/core.py
+++ b/aptdaemon/core.py
@@ -60,7 +60,7 @@ from . import enums
from defer import inline_callbacks, return_value, Deferred
from defer.utils import dbus_deferred_method
from . import policykit1
-from .utils import split_package_id
+from .utils import split_package_id, set_euid_egid
from .worker import DummyWorker
from .worker.aptworker import (AptWorker,
trans_only_installs_pkgs_from_high_trust_repos)
@@ -1107,24 +1107,28 @@ class Transaction(DBusObject):
"""
if self.status != enums.STATUS_SETTING_UP:
raise errors.TransactionAlreadyRunning()
- if not os.access(ttyname, os.W_OK):
- raise errors.AptDaemonError("Pty device does not exist: "
- "%s" % ttyname)
- if not os.stat(ttyname)[4] == self.uid:
- raise errors.AptDaemonError("Pty device '%s' has to be owned by"
- "the owner of the transaction "
- "(uid %s) " % (ttyname, self.uid))
- if os.path.dirname(ttyname) != "/dev/pts":
- raise errors.AptDaemonError("%s isn't a tty" % ttyname)
- try:
- slave_fd = os.open(ttyname, os.O_RDWR | os.O_NOCTTY)
- if os.isatty(slave_fd):
- self.terminal = dbus.String(ttyname)
- self.PropertyChanged("Terminal", self.terminal)
- else:
+ with set_euid_egid(self.uid, self.gid):
+ if os.path.dirname(ttyname) != "/dev/pts":
raise errors.AptDaemonError("%s isn't a tty" % ttyname)
- finally:
- os.close(slave_fd)
+
+ slave_fd = None
+ try:
+ slave_fd = os.open(ttyname, os.O_RDWR | os.O_NOCTTY)
+ except Exception:
+ raise errors.AptDaemonError("Could not open %s" % ttyname)
+ else:
+ if os.fstat(slave_fd).st_uid != self.uid:
+ raise errors.AptDaemonError("Pty device '%s' has to be owned by"
+ "the owner of the transaction "
+ "(uid %s) " % (ttyname, self.uid))
+ if os.isatty(slave_fd):
+ self.terminal = dbus.String(ttyname)
+ self.PropertyChanged("Terminal", self.terminal)
+ else:
+ raise errors.AptDaemonError("%s isn't a tty" % ttyname)
+ finally:
+ if slave_fd is not None:
+ os.close(slave_fd)
def _set_debconf(self, debconf_socket):
"""Set the socket of the debconf proxy.
@@ -1140,13 +1144,17 @@ class Transaction(DBusObject):
"""
if self.status != enums.STATUS_SETTING_UP:
raise errors.TransactionAlreadyRunning()
- if not os.access(debconf_socket, os.W_OK):
- raise errors.AptDaemonError("socket does not exist: "
- "%s" % debconf_socket)
- if not os.stat(debconf_socket)[4] == self.uid:
- raise errors.AptDaemonError("socket '%s' has to be owned by the "
- "owner of the "
- "transaction" % debconf_socket)
+ with set_euid_egid(self.uid, self.gid):
+ try:
+ stat = os.stat(debconf_socket)
+ except Exception:
+ raise errors.AptDaemonError("socket status could not be read: "
+ "%s" % debconf_socket)
+ else:
+ if stat.st_uid != self.uid:
+ raise errors.AptDaemonError("socket '%s' has to be owned by the "
+ "owner of the "
+ "transaction" % debconf_socket)
self.debconf = dbus.String(debconf_socket)
self.PropertyChanged("DebconfSocket", self.debconf)
--- a/aptdaemon/worker/aptworker.py
+++ b/aptdaemon/worker/aptworker.py
@@ -58,6 +58,7 @@ from . import BaseWorker
from ..enums import *
from ..errors import *
from .. import lock
+from ..utils import set_euid_egid
from ..progress import (
DaemonOpenProgress,
DaemonInstallProgress,
@@ -90,25 +91,6 @@ USE_HTTP="yes"
"""
-@contextlib.contextmanager
-def set_euid_egid(uid, gid):
- # no need to drop privs
- if os.getuid() != 0 and os.getgid() != 0:
- yield
- return
- # temporary drop privs
- os.setegid(gid)
- old_groups = os.getgroups()
- os.setgroups([gid])
- os.seteuid(uid)
- try:
- yield
- finally:
- os.seteuid(os.getuid())
- os.setegid(os.getgid())
- os.setgroups(old_groups)
-
-
def trans_only_installs_pkgs_from_high_trust_repos(trans,
whitelist=set()):
"""Return True if this transaction only touches packages in the
--- a/aptdaemon/utils.py
+++ b/aptdaemon/utils.py
@@ -24,7 +24,9 @@ __author__ = "Sebastian Heinlein <devel@
__all__ = ("deprecated", "IsoCodes")
+import os
import sys
+import contextlib
import gettext
import functools
import warnings
@@ -58,6 +60,25 @@ def deprecated(func):
return new_func
+@contextlib.contextmanager
+def set_euid_egid(uid, gid):
+ # no need to drop privs
+ if os.getuid() != 0 and os.getgid() != 0:
+ yield
+ return
+ # temporary drop privs
+ os.setegid(gid)
+ old_groups = os.getgroups()
+ os.setgroups([gid])
+ os.seteuid(uid)
+ try:
+ yield
+ finally:
+ os.seteuid(os.getuid())
+ os.setegid(os.getgid())
+ os.setgroups(old_groups)
+
+
class IsoCodes(object):
"""Provides access to the iso-codes language, script and country
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