On Tue, 2024-02-13 at 11:31 -0500, Stefan Berger wrote: > > On 2/13/24 03:57, Roberto Sassu wrote: > > 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. > > When ecdsa is used for signing files it could get stuck as well and > would need this patch: > > diff --git a/security/integrity/ima/ima_main.c > b/security/integrity/ima/ima_main.c > index 45f1a102c599..2e71dc977d43 100644 > --- a/security/integrity/ima/ima_main.c > +++ b/security/integrity/ima/ima_main.c > @@ -1110,7 +1110,9 @@ EXPORT_SYMBOL_GPL(ima_measure_critical_data); > */ > static int ima_kernel_module_request(char *kmod_name) > { > - if (strncmp(kmod_name, "crypto-pkcs1pad(rsa,", 20) == 0) > + if (strncmp(kmod_name, "crypto-pkcs1pad(rsa,", 20) == 0 || > + strncmp(kmod_name, "crypto-ecdsa-nist-p", 19) == 0 || > + strcmp(kmod_name, "cryptomgr") == 0) > return -EINVAL; > > return 0; > > Rejecting cryptomgr seems necessary in the ecdsa case though I am not > sure what the side effects of rejecting it all the time could be. Thanks. Ok, let's find a proper way once IMA/EVM are moved to the LSM infrastructure. Roberto > Stefan > > > > > 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 > > > >