[PATCH v9 19/25] integrity: Move integrity_kernel_module_request() to IMA

[Stefan Berger]

On 2/12/24 12:56, Paul Moore wrote:
> On Mon, Feb 12, 2024 at 12:48 PM Stefan Berger <stefanb at 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.