linux-kernel - Re: [PATCH] SELinux: Measure state and hash of policy using IMA

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Message-ID: <418618c4-a0c6-6b28-6718-2726a29b83c5@linux.microsoft.com>
Date:   Mon, 24 Aug 2020 11:13:54 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Stephen Smalley <stephen.smalley.work@...il.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        tusharsu@...ux.microsoft.com, sashal@...nel.org,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        SElinux list <selinux@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] SELinux: Measure state and hash of policy using IMA

On 8/24/20 7:00 AM, Stephen Smalley wrote:

>> +int security_read_policy_kernel(struct selinux_state *state,
>> +                               void **data, size_t *len)
>> +{
>> +       int rc;
>> +
>> +       rc = security_read_policy_len(state, len);
>> +       if (rc)
>> +               return rc;
>> +
>> +       *data = vmalloc(*len);
>> +       if (!*data)
>> +               return -ENOMEM;
>>
>> +       return security_read_selinux_policy(state, data, len);
>>   }
> 
> See the discussion here:
> https://lore.kernel.org/selinux/20200824113015.1375857-1-omosnace@redhat.com/T/#t
> 
> In order for this to be safe, you need to ensure that all callers of
> security_read_policy_kernel() have taken fsi->mutex in selinuxfs and
> any use of security_read_policy_len() occurs while holding the mutex.
> Otherwise, the length can change between security_read_policy_len()
> and security_read_selinux_policy() if policy is reloaded.
> 

"struct selinux_fs_info" is available when calling 
security_read_policy_kernel() - currently in measure.c.
Only "struct selinux_state" is.

Is Ondrej's re-try approach I need to use to workaround policy reload issue?

thanks,
  -lakshmi