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Subject: Re: [PATCH v3 12/25] security: Introduce inode_post_setattr hook
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Roberto Sassu <roberto.sassu@huaweicloud.com>,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        chuck.lever@oracle.com, jlayton@kernel.org, neilb@suse.de,
        kolga@netapp.com, Dai.Ngo@oracle.com, tom@talpey.com,
        dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org,
        serge@hallyn.com, dhowells@redhat.com, jarkko@kernel.org,
        stephen.smalley.work@gmail.com, eparis@parisplace.org,
        casey@schaufler-ca.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
        selinux@vger.kernel.org, Roberto Sassu <roberto.sassu@huawei.com>
Date:   Wed, 11 Oct 2023 20:08:53 -0400
In-Reply-To: <20230904133415.1799503-13-roberto.sassu@huaweicloud.com>
References: <20230904133415.1799503-1-roberto.sassu@huaweicloud.com>
         <20230904133415.1799503-13-roberto.sassu@huaweicloud.com>
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gOn Mon, 2023-09-04 at 15:34 +0200, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.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 ...

> 
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>