diff mbox

[v2,02/10] qemu|qtest: Avoid dangerous arguments

Message ID 20170725150951.16038-3-ldoktor@redhat.com
State New
Headers show

Commit Message

Lukáš Doktor July 25, 2017, 3:09 p.m. UTC 
The list object is mutable in python and potentially might modify other
object's arguments when used as default argument. Reproducer:

    >>> vm1 = QEMUMachine("qemu")
    >>> vm2 = QEMUMachine("qemu")
    >>> vm1._wrapper.append("foo")
    >>> print vm2._wrapper
    ['foo']

In this case the `args` is actually copied so it would be safe to keep
it, but it's not a good practice to keep it. The same issue applies in
inherited qtest module.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
---
 scripts/qemu.py  | 6 +++++-
 scripts/qtest.py | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

Comments

John Snow July 25, 2017, 5:14 p.m. UTC | #1 
On 07/25/2017 11:09 AM, Lukáš Doktor wrote:
> The list object is mutable in python and potentially might modify other
> object's arguments when used as default argument. Reproducer:
> 
>      >>> vm1 = QEMUMachine("qemu")
>      >>> vm2 = QEMUMachine("qemu")
>      >>> vm1._wrapper.append("foo")
>      >>> print vm2._wrapper
>      ['foo']
> 
> In this case the `args` is actually copied so it would be safe to keep
> it, but it's not a good practice to keep it. The same issue applies in
> inherited qtest module.
> 

ohh, grr, this trips me up in Python all the time. Definitely best to 
remove such usages where possible.

> Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

Reviewed-by: John Snow <jsnow@redhat.com>
diff mbox

Patch

diff --git a/scripts/qemu.py b/scripts/qemu.py
index 191c916..66fd863 100644
--- a/scripts/qemu.py
+++ b/scripts/qemu.py
@@ -23,7 +23,7 @@  import qmp.qmp
 class QEMUMachine(object):
     '''A QEMU VM'''
 
-    def __init__(self, binary, args=[], wrapper=[], name=None,
+    def __init__(self, binary, args=None, wrapper=None, name=None,
                  test_dir="/var/tmp", monitor_address=None,
                  socket_scm_helper=None, debug=False):
         '''
@@ -39,6 +39,10 @@  class QEMUMachine(object):
         @param debug: enable debug mode (forwarded to QMP helper and such)
         @note: Qemu process is not started until launch() is used.
         '''
+        if args is None:
+            args = []
+        if wrapper is None:
+            wrapper = []
         if name is None:
             name = "qemu-%d" % os.getpid()
         if monitor_address is None:
diff --git a/scripts/qtest.py b/scripts/qtest.py
index d5aecb5..ab183c0 100644
--- a/scripts/qtest.py
+++ b/scripts/qtest.py
@@ -79,7 +79,7 @@  class QEMUQtestProtocol(object):
 class QEMUQtestMachine(qemu.QEMUMachine):
     '''A QEMU VM'''
 
-    def __init__(self, binary, args=[], name=None, test_dir="/var/tmp",
+    def __init__(self, binary, args=None, name=None, test_dir="/var/tmp",
                  socket_scm_helper=None):
         if name is None:
             name = "qemu-%d" % os.getpid()