On 5/3/2018 8:51 AM, Eric W. Biederman wrote: > Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes: > >> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote: >>> Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes: >>> >>>> Allow LSMs and IMA to differentiate between the kexec_load and >>>> kexec_file_load syscalls by adding an "unnecessary" call to >>>> security_kernel_read_file() in kexec_load. This would be similar to the >>>> existing init_module syscall calling security_kernel_read_file(). >>> Given the reasonable desire to load a policy that ensures everything >>> has a signature I don't have fundamental objections. >>> >>> security_kernel_read_file as a hook seems an odd choice. At the very >>> least it has a bad name because there is no file reading going on here. >>> >>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested >>> anywhere. Which means I could have a kernel compiled without that and I >>> would be allowed to use kexec_file_load without signature checking. >>> While kexec_load would be denied. >>> >>> Am I missing something here? >> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn >> calls security_kernel_read_file(). So kexec_file_load and kexec_load >> syscall would be using the same method for enforcing signature >> verification. > Having looked at your patches and the kernel a little more I think > this should be a separate security hook that does not take a file > parameter. > > Right now every other security module assumes !file is init_module. > So I think this change has the potential to confuse other security > modules, with the result of unintended policy being applied. > > So just for good security module hygeine I think this needs a dedicated > kexec_load security hook. I would rather see the existing modules updated than a new hook added. Too many hooks spoil the broth. Two hooks with trivial differences just add to the clutter and make it harder for non-lsm developers to figure out what to use in their code.
