linux-kernel - Re: [PATCH v8 19/24] ima: Move to LSM infrastructure

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Date: Wed, 27 Dec 2023 14:52:40 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Casey Schaufler <casey@...aufler-ca.com>,
        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, 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 19/24] ima: Move to LSM infrastructure

On Tue, 2023-12-26 at 12:14 -0800, Casey Schaufler wrote:
> On 12/26/2023 10:14 AM, Mimi Zohar wrote:
> > On Thu, 2023-12-14 at 18:08 +0100, Roberto Sassu wrote:
> >> From: Roberto Sassu <roberto.sassu@...wei.com>
> >>
> >> Move hardcoded IMA function calls (not appraisal-specific functions) from
> >> various places in the kernel to the LSM infrastructure, by introducing a
> >> new LSM named 'ima' (at the end of the LSM list and always enabled like
> >> 'integrity').
> >>
> >> Having IMA before EVM in the Makefile is sufficient to preserve the
> >> relative order of the new 'ima' LSM in respect to the upcoming 'evm' LSM,
> >> and thus the order of IMA and EVM function calls as when they were
> >> hardcoded.
> >>
> >> Make moved functions as static (except ima_post_key_create_or_update(),
> >> which is not in ima_main.c), and register them as implementation of the
> >> respective hooks in the new function init_ima_lsm().
> >>
> >> A slight difference is that IMA and EVM functions registered for the
> >> inode_post_setattr, inode_post_removexattr, path_post_mknod,
> >> inode_post_create_tmpfile, inode_post_set_acl and inode_post_remove_acl
> >> won't be executed for private inodes. Since those inodes are supposed to be
> >> fs-internal, they should not be of interest of IMA or EVM. The S_PRIVATE
> >> flag is used for anonymous inodes, hugetlbfs, reiserfs xattrs, XFS scrub
> >> and kernel-internal tmpfs files.
> >>
> >> Conditionally register ima_post_path_mknod() if CONFIG_SECURITY_PATH is
> >> enabled, otherwise the path_post_mknod hook won't be available.
> > Up to this point, enabling CONFIG_SECURITY_PATH was not required.  By
> > making it conditional on CONFIG_SECURITY_PATH, anyone enabling IMA will
> > also need to enable CONFIG_SECURITY_PATH.  Without it, new files will
> > not be tagged as a "new" file.
> >
> > Casey, Paul, how common is it today not to enable CONFIG_SECURITY_PATH?
> > Will enabling it just for IMA be a problem?
> 
> Landlock, AppArmor and TOMOYO require it. Fedora enables Landlock and Ubuntu
> enables AppArmor. I expect that, except for "minimal" distributions, you
> won't get any push back. If a distribution is striving for minimal, it's not
> going to use IMA.
> 
> It makes me wonder if eliminating CONFIG_SECURITY_PATH might not be a
> rational alternative.

Embedded systems were the first to use IMA for file signature
verification, not distros.               Could they have enabled
SELinux, lockdown, and IMA?

Mimi