Re: [PATCH V5 2/2] IMA: Support using new creds in appraisal policy

Mimi Zohar
2018-01-08T19:56:03Z

On Mon, 2018-01-08 at 11:45 -0800, Matthew Garrett wrote:
> On Mon, Jan 8, 2018 at 4:18 AM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> > On Fri, 2018-01-05 at 13:15 -0800, Matthew Garrett wrote:
> >> The existing BPRM_CHECK functionality in IMA validates against the
> >> credentials of the existing process, not any new credentials that the
> >> child process may transition to. Add an additional CREDS_CHECK target
> >> and refactor IMA to pass the appropriate creds structure. In
> >> ima_bprm_check(), check with both the existing process credentials and
> >> the credentials that will be committed when the new process is started.
> >> This will not change behaviour unless the system policy is extended to
> >> include CREDS_CHECK targets - BPRM_CHECK will continue to check the same
> >> credentials that it did previously.
> >
> > Refactoring IMA to pass the creds structure all the way down is a
> > generic solution, but if the CREDS_CHECK rule is only being called
> > from ima_bprm_check(), "container_of" the bprm->file returns a pointer
> > to the bprm structure. Perhaps you could limit the amount of
> > refactoring needed based on the func.
>
> Hm. This would avoid adding an argument to process_measurement(), but
> we'd still need to pass additional information down through
> ima_get_action() in order to get the creds and secid right. It feels a
> little ugly to have process_measurement() recreate information rather
> than having the caller pass it in, but I'm not going to object.

Agreed. Initially, I was thinking that only ima_match_rules() would
use container_of, but the very first thing process_measurement() does
is get the inode from the file. Everything afterwards passes the
inode.

> > Could you include in the patch description a simple method for testing
> > this change?
>
> Certainly.

Thanks!

Mimi