Re: [Qemu-devel] [PATCH 02/11] qemu.py: Avoid dangerous arguments

[Philippe Mathieu-Daudé]

On 07/20/2017 01:28 PM, 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.
>
> Signed-off-by: Lukáš Doktor <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
>   scripts/qemu.py | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> 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: