Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace

Stefan Berger
2021-12-10T14:17:38Z

On 12/10/21 08:02, Mimi Zohar wrote:
> On Fri, 2021-12-10 at 07:40 -0500, Stefan Berger wrote:
>> On 12/10/21 07:09, Mimi Zohar wrote:
>>> On Fri, 2021-12-10 at 12:49 +0100, Christian Brauner wrote:
>>>>> There's still the problem that if you write the policy, making the file
>>>>> disappear then unmount and remount securityfs it will come back. My
>>>>> guess for fixing this is that we only stash the policy file reference,
>>>>> create it if NULL but then set the pointer to PTR_ERR(-EINVAL) or
>>>>> something and refuse to create it for that value.
>>>> Some sort of indicator that gets stashed in struct ima_ns that the file
>>>> does not get recreated on consecutive mounts. That shouldn't be hard to
>>>> fix.
>>> The policy file disappearing is for backwards compatibility, prior to
>>> being able to extend the custom policy. For embedded usecases,
>>> allowing the policy to be written exactly once might makes sense. Do
>>> we really want/need to continue to support removing the policy in
>>> namespaces?
>> I don't have an answer but should the behavior for the same #define in
>> this case be different for host and namespaces? Or should we just
>> 'select IMA_WRITE_POLICY and IMA_READ_POLICY' when IMA_NS is selected?
> The latter option sounds good. Being able to analyze the namespace
> policy is really important.

Ok, I will adjust the Kconfig for this then. This then warrants the
question whether to move the dentry into the ima_namespace. The current
code looks like this.

#if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)
securityfs_remove(ns->policy_dentry);
ns->policy_dentry = NULL;
ns->policy_dentry_removed = true;
#elif defined(CONFIG_IMA_WRITE_POLICY)

With IMA_NS selecting IMA_WRITE_POLICY and IMA_READ_POLICY the above
wouldn't be necessary anymore but I find it 'cleaner' to still have the
dentry isolated rather than it being a global static as it was before...

>
> thanks,
>
> Mimi
>