Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] SELinux: Measure state and hash of policy using IMA
To:     Stephen Smalley <stephen.smalley.work@gmail.com>
Cc:     Mimi Zohar <zohar@linux.ibm.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Tyler Hicks <tyhicks@linux.microsoft.com>,
        tusharsu@linux.microsoft.com, sashal@kernel.org,
        James Morris <jmorris@namei.org>,
        linux-integrity@vger.kernel.org,
        SElinux list <selinux@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <20200822010018.19453-1-nramas@linux.microsoft.com>
 <CAEjxPJ5Kok-TBfS=XQ+NUC5tuaZRkyLBOawG4UDky51_bsMnGw@mail.gmail.com>
From:   Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Message-ID: <4eec93aa-2c32-8422-f62b-b101a0d0028a@linux.microsoft.com>
Date:   Mon, 24 Aug 2020 07:35:55 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <CAEjxPJ5Kok-TBfS=XQ+NUC5tuaZRkyLBOawG4UDky51_bsMnGw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 8/24/20 7:00 AM, Stephen Smalley wrote:
> On Fri, Aug 21, 2020 at 9:00 PM Lakshmi Ramasubramanian

> 
>> +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.
> 

Thanks. I'll make this change.

  -lakshmi