linux-kernel - Re: [PATCH v3 12/25] security: Introduce inode_post

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Date:   Thu, 12 Oct 2023 07:43:36 -0400
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,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v3 12/25] security: Introduce inode_post_setattr hook

On Thu, 2023-10-12 at 09:42 +0200, Roberto Sassu wrote:
> On Wed, 2023-10-11 at 20:08 -0400, Mimi Zohar wrote:
> > gOn Mon, 2023-09-04 at 15:34 +0200, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@...wei.com>
> > > 
> > > In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> > > the inode_post_setattr hook.
> > > 
> > > It is useful for EVM to recalculate the HMAC on modified file attributes
> > > and other file metadata, after it verified the HMAC of current file
> > > metadata with the inode_setattr hook.
> > 
> > "useful"?  
> > 
> > At inode_setattr hook, EVM verifies the file's existing HMAC value.  At
> > inode_post_setattr, EVM re-calculates the file's HMAC based on the
> > modified file attributes and other file metadata.
> > 
> > > 
> > > LSMs should use the new hook instead of inode_setattr, when they need to
> > > know that the operation was done successfully (not known in inode_setattr).
> > > The new hook cannot return an error and cannot cause the operation to be
> > > reverted.
> > 
> > Other LSMs could similarly update security xattrs or ...
> 
> I added your sentence. The one above is to satisfy Casey's request to
> justify the addition of the new hook, and to explain why inode_setattr
> is not sufficient.

I was suggesting simplifying the wording.  Perhaps something like:

Other LSMs could similarly take some action after successful file attri
bute change.

-- 
thanks,

Mimi