On Mon, 2020-12-28 at 12:06 -0800, Casey Schaufler wrote:
> On 12/28/2020 11:24 AM, Mimi Zohar wrote:
> > Hi Casey,
> >
> > On Fri, 2020-11-20 at 12:14 -0800, Casey Schaufler wrote:
> >> diff --git a/security/security.c b/security/security.c
> >> index 5da8b3643680..d01363cb0082 100644
> >> --- a/security/security.c
> >> +++ b/security/security.c
> >>
> >> @@ -2510,7 +2526,24 @@ int security_key_getsecurity(struct key *key, char
> >> **_buffer)
> >>
> >> int security_audit_rule_init(u32 field, u32 op, char *rulestr, void
> >> **lsmrule)
> >> {
> >> - return call_int_hook(audit_rule_init, 0, field, op, rulestr,
> >> lsmrule);
> >> + struct security_hook_list *hp;
> >> + bool one_is_good = false;
> >> + int rc = 0;
> >> + int trc;
> >> +
> >> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_init,
> >> list) {
> >> + if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >=
> >> lsm_slot))
> >> + continue;
> >> + trc = hp->hook.audit_rule_init(field, op, rulestr,
> >> + &lsmrule[hp->lsmid->slot]);
> >> + if (trc == 0)
> >> + one_is_good = true;
> >> + else
> >> + rc = trc;
> >> + }
> >> + if (one_is_good)
> >> + return 0;
> >> + return rc;
> >> }
> > So the same string may be defined by multiple LSMs.
>
> Yes. Any legal AppArmor label would also be a legal Smack label.
>
> >> int security_audit_rule_known(struct audit_krule *krule)
> >> @@ -2518,14 +2551,31 @@ int security_audit_rule_known(struct audit_krule
> >> *krule)
> >> return call_int_hook(audit_rule_known, 0, krule);
> >> }
> >>
> >> -void security_audit_rule_free(void *lsmrule)
> >> +void security_audit_rule_free(void **lsmrule)
> >> {
> >> - call_void_hook(audit_rule_free, lsmrule);
> >> + struct security_hook_list *hp;
> >> +
> >> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_free,
> >> list) {
> >> + if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >=
> >> lsm_slot))
> >> + continue;
> >> + hp->hook.audit_rule_free(lsmrule[hp->lsmid->slot]);
> >> + }
> >> }
> >>
> > If one LSM frees the string, then the string is deleted from all LSMs.
> > I don't understand how this safe.
>
> The audit system doesn't have a way to specify which LSM
> a watched label is associated with. Even if we added one,
> we'd still have to address the current behavior. Assigning
> the watch to all modules means that seeing the string
> in any module is sufficient to generate the event.
I originally thought loading a new LSM policy could not delete existing
LSM labels, but that isn't true. If LSM labels can come and go based
on policy, with this code, could loading a new policy for one LSM
result in deleting labels of another LSM?
>
> >
> >> -int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule)
> >> +int security_audit_rule_match(u32 secid, u32 field, u32 op, void
> >> **lsmrule)
> >> {
> >> - return call_int_hook(audit_rule_match, 0, secid, field, op,
> >> lsmrule);
> >> + struct security_hook_list *hp;
> >> + int rc;
> >> +
> >> + hlist_for_each_entry(hp, &security_hook_heads.audit_rule_match,
> >> list) {
> >> + if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >=
> >> lsm_slot))
> >> + continue;
> >> + rc = hp->hook.audit_rule_match(secid, field, op,
> >> + &lsmrule[hp->lsmid->slot]);
> >> + if (rc)
> >> + return rc;
> > Suppose that there is an IMA dont_measure or dont_appraise rule, if one
> > LSM matches, then this returns true, causing any measurement or
> > integrity verification to be skipped.
>
> Yes, that is correct. Like the audit system, you're doing a string based
> lookup, which pretty well has to work this way. I have proposed compound
> label specifications in the past, but even if we accepted something like
> "apparmor=dates,selinux=figs" we'd still have to be compatible with the
> old style inputs.
>
> >
> > Sample policy rules:
> > dont_measure obj_type=foo_log
> > dont_appraise obj_type=foo_log
IMA could extend the existing policy rules like "lsm=[selinux] |
[smack] | [apparmor]", but that assumes that the underlying
infrastructure supports it.
> >
> > Are there any plans to prevent label collisions or at least notify of a
> > label collision?
>
> What would that look like? You can't say that Smack isn't allowed
> to use valid AppArmor labels. How would Smack know? If the label is
> valid to both, how would you decide which LSM gets to use it?
As this is a runtime issue, when loading a new policy at least flag the
collision. When removing the label, when it is defined by multiple
LSMs, at least flag the removal.
>
> >
> >> + }
> >> + return 0;
> >> }
> >> #endif /* CONFIG_AUDIT */
>
