[PATCH V3 2/2] IMA: Support using new creds in appraisal policy

[Matthew Garrett]

On Tue, Nov 28, 2017 at 12:48 PM, Mimi Zohar <zohar at linux.vnet.ibm.com> wrote:
> Hi Matthew,
>
> On Thu, 2017-10-26 at 01:40 -0700, 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.
>
> < snip >
>
> > @@ -305,7 +304,7 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
> >               case LSM_SUBJ_USER:
> >               case LSM_SUBJ_ROLE:
> >               case LSM_SUBJ_TYPE:
> > -                     security_task_getsecid(tsk, &sid);
> > +                     security_cred_getsecid(cred, &sid);
> >                       rc = security_filter_rule_match(sid,
> >                                                       rule->lsm[i].type,
> >                                                       Audit_equal,
>
> Based on the patch description, I wouldn't expect to see any changes
> here, unless this is wrong to begin with.  In which case, it should be
> a separate patch.

We need to check against the appropriate credentials structure, and
since we're doing this before commit_creds() has been called we can't
just do it against the one in the task structure. For BPRM_CHECK
that'll be current_cred(), which means there's no change in
functionality, whereas for CREDS_CHECK it'll be the new credentials
structure.
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