linux-kernel - Re: [PATCH 4/5] evm: Use the real inode's metadata to calculate metadata hash

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Date: Fri, 2 Feb 2024 09:59:17 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Amir Goldstein <amir73il@...il.com>
Cc: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        zohar@...ux.ibm.com, roberto.sassu@...wei.com, miklos@...redi.hu
Subject: Re: [PATCH 4/5] evm: Use the real inode's metadata to calculate
 metadata hash



On 2/2/24 04:24, Amir Goldstein wrote:
> On Thu, Feb 1, 2024 at 10:35 PM Stefan Berger <stefanb@...ux.ibm.com> wrote:

> 
>>
>> and your suggested change to this patch :
>>
>> -       struct inode *inode = d_real_inode(dentry);
>> +       struct inode *inode = d_inode(d_real(dentry, false));;
>>
> 
> In the new version I change the API to use an enum instead of bool, e.g.:
> 
>         struct inode *inode = d_inode(d_real(dentry, D_REAL_METADATA));

Thanks. I will use it.

> 
> This catches in build time and in run time, callers that were not converted
> to the new API.
> 
>> The test cases are now passing with and without metacopy enabled. Yay!
> 
> Too soon to be happy.
> I guess you are missing a test for the following case:
> 1. file was meta copied up (change is detected)
> 2. the lower file that contains the data is being changed (change is
> not detected)

Right. Though it seems there's something wrong with overlayfs as well 
after appending a byte to the file on the lower.

-rwxr-xr-x    1 0        0               25 Feb  2 14:55 
/ext4.mount/lower/test_rsa_portable2
-rwxr-xr-x    1 0        0               24 Feb  2 14:55 
/ext4.mount/overlay/test_rsa_portable2
bb16aa5350bcc8863da1a873c846fec9281842d9 
/ext4.mount/lower/test_rsa_portable2
bb16aa5350bcc8863da1a873c846fec9281842d9 
/ext4.mount/overlay/test_rsa_portable2

We have a hash collision on a file with 24 bytes and the underlying one 
with 25 byte. (-;  :-)

   Stefan