For completeness, the security bug was about untrusted remote data (from
facts) being used to add arguments to commands in playbooks if things were
formatted in ways that would allow it.
I can't say I entirely follow the omit proposal but I think I get the gist.
However, it's better if we can do something that covers both key=value
and longform arguments. I like the following idea a little better:
Basically what would need to be done here is to teach the code what to do
if the gid was None, and introduce the concept that None meant "no change"
as if the argument was not set.
This may require something on argument_spec (sorry, code internals) that
looks like
argument_spec = dict(
param = dict(name='foo', required=False, nullable=True)
)
And if the param is "None" or "", it would be /removed/ from the input
parameter list, if set nullable.
For completeness, you have the following workaround available now but
probably won't like it:
- module_name: foo=bar
when: baz is undefined
- module_name: foo=bar baz={{ baz }}
when: baz is defined
I understand that's not perfect, but we do need to protect against variable
additions.
In my proposal, you could still do
- module_name: foo=bar baz={{ baz }}
Because baz should insert None if set None. if undefined, needs to be
|default(None).
On Mon, Jul 28, 2014 at 8:34 PM, Michael DeHaan <[email protected]> wrote:
> Replying shortly.
>
> For clarity purposes what you have selected in the original pastebin which
> is no longer legal was:
>
> - name: generic-users | Make sure all groups are present
> group: name={{item.name}}{% if item.system is defined %} {{item.system}}{%
> endif %}{% if item.gid is defined %} gid={{item.gid}}{% endif %} state=present
> with_items: genericusers_groups
>
>
>
> On Mon, Jul 28, 2014 at 8:30 PM, Victor Lin <[email protected]> wrote:
>
>> I noticed that since the new ansible with security patched is released,
>> many our roles and playbooks are broken. For example, our role depends on
>> this, it is also broken
>>
>> https://github.com/Ansibles/generic-users/blob/master/tasks/main.yml#L3-L5
>>
>> since it uses if else statements to generate optional arguments like gid.
>> In the latest version of Ansible, it adds new arguments, so it fails to
>> pass security check, an error like
>>
>> A variable inserted a new parameter into the module args. Be sure to
>> quote variables if they contain equal signs (for example: "{{var}}").
>>
>> is raised.
>>
>> I tried to modify the way arguments are passed by leveraging default
>> filter
>>
>> - name: generic-users | Make sure all groups are present
>> group: >
>> name="{{ item.name }}"
>> system="{{ item.system|default('no') }}"
>> gid="{{ item.gid|default(None) }}"
>> state=present
>> with_items: genericusers_groups
>>
>>
>> For argument "system", there is a value "no" I can use as a default
>> value, no problem at all. But for "gid", I tried to feed it with
>> "default(None)", the value will be rendered as string first anyway, so that
>> would be gid=None, ValueError be raised. As a result, unavoidable, I need
>> to pass a valid value to gid.
>>
>> I saw some discuss in this issue report:
>> https://github.com/ansible/ansible/issues/8233
>>
>> I understand that for security reason, if-else statements in playbook are
>> not welcomed, but the problem is without if-else statements, I have no idea
>> how to omit arguments without "do not set anything for this" value. The
>> problem is a little bit like Python's not set default value, we usually
>> create an object stands for not_set value like this
>>
>> NOT_SET = object()
>>
>> def foobar(value=NOT_SET):
>> pass
>>
>> But in ansible, I didn't see anything like that. Or did I miss something?
>> I think it would be helpful if there is some kind of special filter like
>>
>> - name: generic-users | Make sure all groups are present
>> group: >
>> name="{{ item.name }}"
>> system="{{ item.system|default('no') }}"
>> gid="{{ item.gid|default_omit) }}"
>> state=present
>> with_items: genericusers_groups
>>
>> The default_omit filter here omits "gid" argument if it is not defined.
>> Just an idea. However, since modifying context in a jinja2 template would
>> be difficult to implement, I think maybe it's better to encourage YAML
>> style arguments like this:
>>
>> - name: generic-users | Make sure all groups are present
>> group:
>> name: "{{ item.name }}"
>> system: "{{ item.system|default('no') }}"
>> gid: "{{ item.gid|default_omit) }}"
>> state=present
>> with_items: genericusers_groups
>>
>> And for the default_omit, maybe it can return a random nonce generated by
>> system (so that attacker cannot inject this value to remove argument), like
>> this
>>
>> __omit_place_holder_8843d7f92416211de9ebb963ff4ce28125932878__
>>
>> And when ansible sees this value for a argument, it simply remove the key
>> from arguments instead of passing it down to module.
>>
>> But anyway, these are just some thinkings, the more important thing is, I
>> would like to know, at this moment, how can I solve that "gid" cannot be
>> omit issue? Is there any workaround? There are so many modules there, if
>> you give an argument there, it means you want to change that thing, and
>> there is no not_set value.
>>
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