Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <b7e3b342-9b88-7698-9e9d-f81a6f79c395@linux.ibm.com>
Date:   Thu, 6 Apr 2023 17:58:59 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM after
 writes
Content-Language: en-US
To:     Jeff Layton <jlayton@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Paul Moore <paul@paul-moore.com>
Cc:     zohar@linux.ibm.com, linux-integrity@vger.kernel.org,
        miklos@szeredi.hu, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org,
        amir73il@gmail.com
References: <20230405171449.4064321-1-stefanb@linux.ibm.com>
 <20230406-diffamieren-langhaarig-87511897e77d@brauner>
 <CAHC9VhQsnkLzT7eTwVr-3SvUs+mcEircwztfaRtA+4ZaAh+zow@mail.gmail.com>
 <a6c6e0e4-047f-444b-3343-28b71ddae7ae@linux.ibm.com>
 <CAHC9VhQyWa1OnsOvoOzD37EmDnESfo4Rxt2eCSUgu+9U8po-CA@mail.gmail.com>
 <20230406-wasser-zwanzig-791bc0bf416c@brauner>
 <546145ecbf514c4c1a997abade5f74e65e5b1726.camel@kernel.org>
 <45a9c575-0b7e-f66a-4765-884865d14b72@linux.ibm.com>
 <60339e3bd08a18358ac8c8a16dc67c74eb8ba756.camel@kernel.org>
 <d61ed13b-0fd2-0283-96d2-0ff9c5e0a2f9@linux.ibm.com>
 <4f739cc6847975991874d56ef9b9716c82cf62a3.camel@kernel.org>
From:   Stefan Berger <stefanb@linux.ibm.com>
In-Reply-To: <4f739cc6847975991874d56ef9b9716c82cf62a3.camel@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
Precedence: bulk


On 4/6/23 17:24, Jeff Layton wrote:
> On Thu, 2023-04-06 at 16:22 -0400, Stefan Berger wrote:
>>
>> On 4/6/23 15:37, Jeff Layton wrote:
>>> On Thu, 2023-04-06 at 15:11 -0400, Stefan Berger wrote:
>>>>
>>>> On 4/6/23 14:46, Jeff Layton wrote:
>>>>> On Thu, 2023-04-06 at 17:01 +0200, Christian Brauner wrote:
>>>>>> On Thu, Apr 06, 2023 at 10:36:41AM -0400, Paul Moore wrote:
>>>>
>>>>>
>>>>> Correct. As long as IMA is also measuring the upper inode then it seems
>>>>> like you shouldn't need to do anything special here.
>>>>
>>>> Unfortunately IMA does not notice the changes. With the patch provided in the other email IMA works as expected.
>>>>
>>>
>>>
>>> It looks like remeasurement is usually done in ima_check_last_writer.
>>> That gets called from __fput which is called when we're releasing the
>>> last reference to the struct file.
>>>
>>> You've hooked into the ->release op, which gets called whenever
>>> filp_close is called, which happens when we're disassociating the file
>>> from the file descriptor table.
>>>
>>> So...I don't get it. Is ima_file_free not getting called on your file
>>> for some reason when you go to close it? It seems like that should be
>>> handling this.
>>
>> I would ditch the original proposal in favor of this 2-line patch shown here:
>>
>> https://lore.kernel.org/linux-integrity/a95f62ed-8b8a-38e5-e468-ecbde3b221af@linux.ibm.com/T/#m3bd047c6e5c8200df1d273c0ad551c645dd43232
>>
>>
> 
> Ok, I think I get it. IMA is trying to use the i_version from the
> overlayfs inode.
> 
> I suspect that the real problem here is that IMA is just doing a bare
> inode_query_iversion. Really, we ought to make IMA call
> vfs_getattr_nosec (or something like it) to query the getattr routine in
> the upper layer. Then overlayfs could just propagate the results from
> the upper layer in its response.

You mean compare known stat against current ? It seems more expensive to stat the file
rather than using the simple i_version-has-changed indicator.

> 
> That sort of design may also eventually help IMA work properly with more
> exotic filesystems, like NFS or Ceph.

And these don't support i_version at all?

    Stefan