On Mon, 2024-02-12 at 15:28 -0500, Stefan Berger wrote: > > On 2/12/24 12:56, Paul Moore wrote: > > On Mon, Feb 12, 2024 at 12:48 PM Stefan Berger <stefanb@xxxxxxxxxxxxx> 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. I can be even more precise I guess (I actually reproduced it). Avoid a verification loop where verifying the signature of the modprobe binary requires executing modprobe itself. Since the modprobe iint- >mutex is already held when the signature verification is performed, a deadlock occurs as soon as modprobe is executed within the critical region, since the same lock cannot be taken again. This happens 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 a 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(), and avoid the verification loop. Roberto
