linux-kernel - RE: [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY

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Date:   Tue, 4 May 2021 13:16:03 +0000
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        "mjg59@...gle.com" <mjg59@...gle.com>
CC:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS
 if conditions are safe

> From: Mimi Zohar [mailto:zohar@...ux.ibm.com]
> Sent: Monday, May 3, 2021 4:35 PM
> On Mon, 2021-05-03 at 14:15 +0000, Roberto Sassu wrote:
> 
> > > > >  	if (evm_status != INTEGRITY_PASS)
> > > > >  		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
> > > > d_backing_inode(dentry),
> > > > >  				    dentry->d_name.name,
> > > > "appraise_metadata",
> > > > > @@ -515,7 +535,8 @@ int evm_inode_setattr(struct dentry *dentry,
> > > struct
> > > > iattr *attr)
> > > > >  		return 0;
> > > > >  	evm_status = evm_verify_current_integrity(dentry);
> > > > >  	if ((evm_status == INTEGRITY_PASS) ||
> > > > > -	    (evm_status == INTEGRITY_NOXATTRS))
> > > > > +	    (evm_status == INTEGRITY_NOXATTRS) ||
> > > > > +	    (evm_ignore_error_safe(evm_status)))
> > > >
> > > > It would also remove the INTEGRITY_NOXATTRS test duplication here.
> > >
> > > Ok.
> >
> > Actually, it does not seem a duplication. Currently, INTEGRITY_NOXATTRS
> > is ignored also when the HMAC key is loaded.
> 
> The existing INTEGRITY_NOXATTRS exemption is more general and includes
> the new case of when EVM HMAC is disabled.  The additional exemption is
> only needed for INTEGRITY_NOLABEL, when EVM HMAC is disabled.

Unfortunately, evm_ignore_error_safe() is called by both evm_protect_xattr()
and evm_inode_setattr(). The former requires an exemption also for
INTEGRITY_NOXATTRS.

I would keep the function as it is. In the worst case, when the status is
INTEGRITY_NOXATTRS in evm_inode_setattr(), the function will not
be called.

Roberto

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