linux-kernel - Re: [PATCH v5 15/16] ima: Move dentries into ima

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Message-ID: <66b377f6-40b4-77da-c02b-2650fa72d0b4@linux.ibm.com>
Date:   Fri, 10 Dec 2021 09:17:14 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        James Bottomley <jejb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, serge@...lyn.com,
        containers@...ts.linux.dev, dmitry.kasatkin@...il.com,
        ebiederm@...ssion.com, krzysztof.struczynski@...wei.com,
        roberto.sassu@...wei.com, mpeters@...hat.com, lhinds@...hat.com,
        lsturman@...hat.com, puiterwi@...hat.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org
Subject: Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace


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
>