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Message-ID: <80e4a1ea172edb2d4d441b70dcd93bfa1654a5b7.camel@huaweicloud.com>
Subject: Re: [PATCH v3 12/25] security: Introduce inode_post_setattr hook
From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
To:     Mimi Zohar <zohar@linux.ibm.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:   Thu, 12 Oct 2023 09:42:58 +0200
In-Reply-To: <22761c3d88c2c4dbac747cc7ddca3d743c6d88d9.camel@linux.ibm.com>
References: <20230904133415.1799503-1-roberto.sassu@huaweicloud.com>
         <20230904133415.1799503-13-roberto.sassu@huaweicloud.com>
         <22761c3d88c2c4dbac747cc7ddca3d743c6d88d9.camel@linux.ibm.com>
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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@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 ...

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