> On Feb 10, 2020, at 1:33 PM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > On Mon, 2020-02-10 at 12:24 -0700, Eric Snowberg wrote: >>> On Feb 10, 2020, at 10:09 AM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > >>>> >>>> Ok, understood, “modsig” refers to strictly kernel module appended signatures >>>> without regard to the keyring that verifies it. Since there are inconsistencies >>>> here, would you consider something like my first patch? It will verify an >>>> uncompressed kernel module containing an appended signature when the public key >>>> is contained within the kernel keyring instead of the ima keyring. Why force a >>>> person to add the same keys into the ima keyring for validation? Especially when >>>> the kernel keyring is now used to verify appended signatures in the compressed >>>> modules. >>> >>> Different use case scenarios have different requirements. Suppose for >>> example that the group creating the kernel image is not the same as >>> using it. The group using the kernel image could sign all files, >>> including kernel modules (imasig), with their own private key. Only >>> files that they signed would be permitted. Your proposal would break >>> the current expectations, allowing kernel modules signed by someone >>> else to be loaded. >>> >> >> All the end user needs to do is compress any module created by the group that built >> the original kernel image to work around the scenario above. Then the appended >> signature in the compressed module will be verified by the kernel keyring. Does >> this mean there is a security problem that should be fixed, if this is a concern? > > Again, the issue isn't compressed/uncompressed kernel modules, but the > syscall used to load the kernel module. IMA can prevent using the the > init_module syscall. Refer to the ima_load_data() LOADING_MODULE > case. Within the ima_load_data() LOADING_MODULE case, to prevent IMA from using the init_module syscall, is_module_sig_enforced() must return false. Currently when is_module_sig_enforced() returns true, the kernel keyring is always used for verification. What if I change this part of my patch from + if (rc && func == MODULE_CHECK) to + sig_enforce = is_module_sig_enforced(); + if (sig_enforce && rc && func == MODULE_CHECK) Now when the init_module syscall is available, finit_module syscall will use both the ima keyring and kernel keyring for verification. When the init_module syscall is blocked from use, the finit_module syscall will only use the ima keyring for validation. I believe this would satisfy both your use case and mine.
