linux-kernel - Re: [PATCH v9 19/25] integrity: Move integrity_kernel_module

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Date: Mon, 12 Feb 2024 15:28:33 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Paul Moore <paul@...l-moore.com>
Cc: Roberto Sassu <roberto.sassu@...weicloud.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,
        jmorris@...ei.org, serge@...lyn.com, zohar@...ux.ibm.com,
        dmitry.kasatkin@...il.com, eric.snowberg@...cle.com,
        dhowells@...hat.com, jarkko@...nel.org, stephen.smalley.work@...il.com,
        eparis@...isplace.org, casey@...aufler-ca.com, shuah@...nel.org,
        mic@...ikod.net, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-integrity@...r.kernel.org,
        keyrings@...r.kernel.org, selinux@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v9 19/25] integrity: Move
 integrity_kernel_module_request() to IMA



On 2/12/24 12:56, Paul Moore wrote:
> On Mon, Feb 12, 2024 at 12:48 PM Stefan Berger <stefanb@...ux.ibm.com> wrote:
>> On 1/15/24 13:18, Roberto Sassu wrote:
> 
> ...
> 
>>> +/**
>>> + * ima_kernel_module_request - Prevent crypto-pkcs1pad(rsa,*) requests
>>> + * @kmod_name: kernel module name
>>> + *
>>> + * We have situation, when public_key_verify_signature() in case of RSA > + * algorithm use alg_name to store internal information in order to
>>> + * construct an algorithm on the fly, but crypto_larval_lookup() will try
>>> + * to use alg_name in order to load kernel module with same name.
>>> + * Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules,
>>> + * we are safe to fail such module request from crypto_larval_lookup().
>>> + *
>>> + * In this way we prevent modprobe execution during digsig verification
>>> + * and avoid possible deadlock if modprobe and/or it's dependencies
>>> + * also signed with digsig.
>>
>> This text needs to some reformulation at some point..
> 
> There is no time like the present.  If you have a suggestion I would
> love to hear it and I'm sure Roberto would too.
> 

My interpretation of the issue after possibly lossy decoding of the 
above sentences:

Avoid a deadlock by rejecting a virtual kernel module with the name 
"crypto-pkcs1pad(rsa,*)". This module may be requested by 
crypto_larval_lookup() while trying to verify an RSA signature in 
public_key_verify_signature(). Since the loading of the RSA module may 
itself cause the request for an RSA signature verification it will 
otherwise lead to a deadlock.