Casey Schaufler <casey@xxxxxxxxxxxxxxxx> writes: > 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. These are not non-trivial differences. There is absolutely nothing file related about kexec_load. Nor for init_module for that matter. If something is called security_kernel_read_file I think it is wholly appropriate for code that processes such a hook to assume file is non-NULL. When you have to dance a jig (which is what I see the security modules doing) to figure out who is calling a lsm hook for what purpose I think it is a maintenance problem waiting to happen and that the hook is badly designed. At this point I don't care what the lsm's do with the hooks but the hooks need to make sense for people outside of the lsm's and something about reading a file in a syscall that doesn't read files is complete and utter nonsense. Eric
