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

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Date:   Thu, 12 Oct 2023 09:42:58 +0200
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, 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 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.

Thanks

Roberto

> > 
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> 
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>