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

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Message-ID: <96f82924cd2fda95f0c89341215e128419bf77fd.camel@linux.ibm.com>
Date: Wed, 27 Dec 2023 14:21:18 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Roberto Sassu <roberto.sassu@...weicloud.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 Wed, 2023-12-27 at 17:39 +0100, Roberto Sassu wrote:
> 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'.

Going forward with the v8 proposed solution would require some real
memory usage analysis for different types of policies.

To me the "integrity: Switch from rbtree to LSM-managed blob for
integrity_iint_cache" makes a lot more sense.   Looking back at the
original thread, your reasons back then for not directly allocating the
integrity_iint_cache are still valid for the ima_iint_cache structure.

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>
>