linux-kernel - Re: [RFC PATCH 0/2] ima: uncompressed module appraisal support

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Date:   Fri, 07 Feb 2020 13:28:45 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>
Cc:     Nayna <nayna@...ux.vnet.ibm.com>, dmitry.kasatkin@...il.com,
        jmorris@...ei.org, serge@...lyn.com, dhowells@...hat.com,
        geert@...ux-m68k.org, gregkh@...uxfoundation.org,
        nayna@...ux.ibm.com, tglx@...utronix.de, bauerman@...ux.ibm.com,
        mpe@...erman.id.au, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] ima: uncompressed module appraisal support

On Fri, 2020-02-07 at 10:49 -0700, Eric Snowberg wrote:
> 
> > On Feb 7, 2020, at 10:40 AM, Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > 
> >> $ insmod ./foo.ko
> >> insmod: ERROR: could not insert module ./foo.ko: Permission denied
> >> 
> >> last entry from audit log:
> >> type=INTEGRITY_DATA msg=audit(1581089373.076:83): pid=2874 uid=0
> >> auid=0 ses=1 subj=unconfined_u:unconfined_r:unconfined_t:s0-
> >> s0:c0.c1023 op=appraise_data cause=invalid-signature comm="insmod"
> >> name="/root/keys/modules/foo.ko" dev="dm-0" ino=10918365
> >> res=0^]UID="root" AUID=“root"
> >> 
> >> This is because modsig_verify() will be called from within
> >> ima_appraise_measurement(), 
> >> since try_modsig is true.  Then modsig_verify() will return
> >> INTEGRITY_FAIL.
> > 
> > Why is it an "invalid signature"?  For that you need to look at the
> > kernel messages.  Most likely it can't find the public key on the .ima
> > keyring to verify the signature.
> 
> It is invalid because the module has not been ima signed. 

With the IMA policy rule "appraise func=MODULE_CHECK
appraise_type=imasig|modsig", IMA first tries to verify the IMA
signature stored as an xattr and on failure then attempts to verify
the appended signatures.

The audit message above indicates that there was a signature, but the
signature validation failed.

Mimi