xsm/flask: clean interdomain event channel hook

Don't attempt to relabel the already-bound half of the event channel
pair created by an interdomain event channel. This relabeling also
performed an incorrect check that the destination domain is permitted
to create the reverse event channel, which may not be true if the
unbound channel was created by the domain builder (like the xenstore
channel).

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Committed-by: Keir Fraser <keir@xen.org>

xen/xsm/flask/hooks.c

@@ -182,12 +182,12 @@ static int flask_evtchn_unbound(struct domain *d1, struct evtchn *chn,
 static int flask_evtchn_interdomain(struct domain *d1, struct evtchn *chn1, 
                                     struct domain *d2, struct evtchn *chn2)
 {
-    u32 newsid1;
-    u32 newsid2;
+    u32 newsid;
     int rc;
-    struct domain_security_struct *dsec1, *dsec2;
+    struct domain_security_struct *dsec, *dsec1, *dsec2;
     struct evtchn_security_struct *esec1, *esec2;
 
+    dsec = current->domain->ssid;
     dsec1 = d1->ssid;
     dsec2 = d2->ssid;
 
@@ -195,7 +195,7 @@ static int flask_evtchn_interdomain(struct domain *d1, struct evtchn *chn1,
     esec2 = chn2->ssid;
 
     rc = security_transition_sid(dsec1->sid, dsec2->sid, 
-                                 SECCLASS_EVENT, &newsid1);
+                                 SECCLASS_EVENT, &newsid);
     if ( rc )
     {
         printk("%s: security_transition_sid failed, rc=%d (domain=%d)\n",
@@ -203,33 +203,19 @@ static int flask_evtchn_interdomain(struct domain *d1, struct evtchn *chn1,
         return rc;
     }
 
-    rc = avc_has_perm(dsec1->sid, newsid1, SECCLASS_EVENT, EVENT__CREATE, NULL);
+    rc = avc_has_perm(dsec->sid, newsid, SECCLASS_EVENT, EVENT__CREATE, NULL);
     if ( rc )
         return rc;
 
-    rc = security_transition_sid(dsec2->sid, dsec1->sid, 
-                                 SECCLASS_EVENT, &newsid2);
-    if ( rc )
-    {
-        printk("%s: security_transition_sid failed, rc=%d (domain=%d)\n",
-               __FUNCTION__, -rc, d1->domain_id);
-        return rc;
-    }
-
-    rc = avc_has_perm(dsec2->sid, newsid2, SECCLASS_EVENT, EVENT__CREATE, NULL);
+    rc = avc_has_perm(newsid, dsec2->sid, SECCLASS_EVENT, EVENT__BIND, NULL);
     if ( rc )
         return rc;
 
-    rc = avc_has_perm(newsid1, dsec2->sid, SECCLASS_EVENT, EVENT__BIND, NULL);
+    rc = avc_has_perm(esec2->sid, dsec1->sid, SECCLASS_EVENT, EVENT__BIND, NULL);
     if ( rc )
         return rc;
 
-    rc = avc_has_perm(newsid2, dsec1->sid, SECCLASS_EVENT, EVENT__BIND, NULL);
-    if ( rc )
-        return rc;    
-
-    esec1->sid = newsid1;
-    esec2->sid = newsid2;
+    esec1->sid = newsid;
 
     return rc;
 }