On 2/12/24 12:56, Paul Moore wrote:

On Mon, Feb 12, 2024 at 12:48 PM Stefan Berger [off-list ref] wrote:

quoted

On 1/15/24 13:18, Roberto Sassu wrote:

...

quoted

quoted

+/**
+ * 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.