linux-kernel - Re: [PATCH v8 23/24] ima: Make it independent from 'integrity' LSM

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Date: Wed, 27 Dec 2023 17:39:06 +0100
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Mimi Zohar <zohar@...ux.ibm.com>, viro@...iv.linux.org.uk,
 brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
 neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
 paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
 dmitry.kasatkin@...il.com, dhowells@...hat.com, jarkko@...nel.org,
 stephen.smalley.work@...il.com, eparis@...isplace.org,
 casey@...aufler-ca.com, shuah@...nel.org, mic@...ikod.net
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
 linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
 selinux@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v8 23/24] ima: Make it independent from 'integrity' LSM

On 12/27/2023 2:22 PM, Mimi Zohar wrote:
> On Thu, 2023-12-14 at 18:08 +0100, Roberto Sassu wrote:
>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>
>> Make the 'ima' LSM independent from the 'integrity' LSM by introducing IMA
>> own integrity metadata (ima_iint_cache structure, with IMA-specific fields
>> from the integrity_iint_cache structure), and by managing it directly from
>> the 'ima' LSM.
>>
>> Move the remaining IMA-specific flags to security/integrity/ima/ima.h,
>> since they are now unnecessary in the common integrity layer.
>>
>> Replace integrity_iint_cache with ima_iint_cache in various places
>> of the IMA code.
>>
>> Then, reserve space in the security blob for the entire ima_iint_cache
>> structure, so that it is available for all inodes having the security blob
>> allocated (those for which security_inode_alloc() was called).  Adjust the
>> IMA code accordingly, call ima_iint_inode() to retrieve the ima_iint_cache
>> structure. Keep the non-NULL checks since there can be inodes without
>> security blob.
> 
> Previously the 'iint' memory was only allocated for regular files in
> policy and were tagged S_IMA.  This patch totally changes when and how
> memory is being allocated.  Does it make sense to allocate memory at
> security_inode_alloc()?  Is this change really necessary for making IMA
> a full fledged LSM?

Good question. I think it wouldn't be necessary, we can reuse the same 
approach as in the patch 'integrity: Switch from rbtree to LSM-managed 
blob for integrity_iint_cache'.

Roberto

> Mimi
> 
>>
>> Don't include the inode pointer as field in the ima_iint_cache structure,
>> since the association with the inode is clear. Since the inode field is
>> missing in ima_iint_cache, pass the extra inode parameter to
>> ima_get_verity_digest().
>>
>> Finally, register ima_inode_alloc_security/ima_inode_free_security() to
>> initialize/deinitialize the new ima_iint_cache structure (before this task
>> was done by iint_init_always() and iint_free()). Also, duplicate
>> iint_lockdep_annotate() for the ima_iint_cache structure, and name it
>> ima_iint_lockdep_annotate().
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>