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Message-ID: <7940b9d0-3133-4b08-b397-ad9ee34e3b34@linux.ibm.com>
Date: Mon, 12 Feb 2024 15:28:33 -0500
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Subject: Re: [PATCH v9 19/25] integrity: Move
 integrity_kernel_module_request() to IMA
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To: Paul Moore <paul@paul-moore.com>
Cc: 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,
        jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com,
        dmitry.kasatkin@gmail.com, eric.snowberg@oracle.com,
        dhowells@redhat.com, jarkko@kernel.org, stephen.smalley.work@gmail.com,
        eparis@parisplace.org, casey@schaufler-ca.com, shuah@kernel.org,
        mic@digikod.net, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org,
        keyrings@vger.kernel.org, selinux@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Roberto Sassu <roberto.sassu@huawei.com>
References: <20240115181809.885385-1-roberto.sassu@huaweicloud.com>
 <20240115181809.885385-20-roberto.sassu@huaweicloud.com>
 <fd6ddc3d-e5d3-4b9c-b00b-ac2b1f22d653@linux.ibm.com>
 <CAHC9VhTY=X7z5SRQZzFe25FGB2E3FBBkuZ_YYA1+ETyr7pv=tA@mail.gmail.com>
From: Stefan Berger <stefanb@linux.ibm.com>
In-Reply-To: <CAHC9VhTY=X7z5SRQZzFe25FGB2E3FBBkuZ_YYA1+ETyr7pv=tA@mail.gmail.com>
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On 2/12/24 12:56, Paul Moore wrote:
> On Mon, Feb 12, 2024 at 12:48 PM Stefan Berger <stefanb@linux.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.