[NSS] Bug 1508776 - Remove unneeded refcounting from SFTKSession

SFTKSession objects are only ever actually destroyed at PK11 session
closure, as the session is always the final holder -- and asserting
refCount == 1 shows that to be true. Because of that, NSC_CloseSession
can just call `sftk_DestroySession` directly and leave
`sftk_FreeSession` as a no-op to be removed in the future.

security/nss/lib/softoken/pkcs11.c

@@ -2674,8 +2674,9 @@ sftk_CloseAllSessions(SFTKSlot *slot, PRBool logout)
             } else {
                 SKIP_AFTER_FORK(PZ_Unlock(lock));
             }
-            if (session)
+            if (session) {
-                sftk_FreeSession(session);
+                sftk_DestroySession(session);
+            }
         } while (session != NULL);
     }
     return CKR_OK;
@@ -3910,8 +3911,6 @@ NSC_CloseSession(CK_SESSION_HANDLE hSession)
     if (sftkqueue_is_queued(session, hSession, slot->head, slot->sessHashSize)) {
         sessionFound = PR_TRUE;
         sftkqueue_delete(session, hSession, slot->head, slot->sessHashSize);
-        session->refCount--; /* can't go to zero while we hold the reference */
-        PORT_Assert(session->refCount > 0);
     }
     PZ_Unlock(lock);
 
@@ -3932,6 +3931,8 @@ NSC_CloseSession(CK_SESSION_HANDLE hSession)
         if (session->info.flags & CKF_RW_SESSION) {
             (void)PR_ATOMIC_DECREMENT(&slot->rwSessionCount);
         }
+        sftk_DestroySession(session);
+        session = NULL;
     }
 
     sftk_FreeSession(session);

security/nss/lib/softoken/pkcs11i.h

@@ -281,7 +281,6 @@ struct SFTKSessionStr {
     SFTKSession *next;
     SFTKSession *prev;
     CK_SESSION_HANDLE handle;
-    int refCount;
     PZLock *objectLock;
     int objectIDCount;
     CK_SESSION_INFO info;
@@ -670,6 +669,7 @@ extern SFTKSlot *sftk_SlotFromSessionHandle(CK_SESSION_HANDLE handle);
 extern CK_SLOT_ID sftk_SlotIDFromSessionHandle(CK_SESSION_HANDLE handle);
 extern SFTKSession *sftk_SessionFromHandle(CK_SESSION_HANDLE handle);
 extern void sftk_FreeSession(SFTKSession *session);
+extern void sftk_DestroySession(SFTKSession *session);
 extern SFTKSession *sftk_NewSession(CK_SLOT_ID slotID, CK_NOTIFY notify,
                                     CK_VOID_PTR pApplication, CK_FLAGS flags);
 extern void sftk_update_state(SFTKSlot *slot, SFTKSession *session);

security/nss/lib/softoken/pkcs11u.c

@@ -1772,7 +1772,6 @@ sftk_NewSession(CK_SLOT_ID slotID, CK_NOTIFY notify, CK_VOID_PTR pApplication,
         return NULL;
 
     session->next = session->prev = NULL;
-    session->refCount = 1;
     session->enc_context = NULL;
     session->hash_context = NULL;
     session->sign_context = NULL;
@@ -1796,11 +1795,10 @@ sftk_NewSession(CK_SLOT_ID slotID, CK_NOTIFY notify, CK_VOID_PTR pApplication,
 }
 
 /* free all the data associated with a session. */
-static void
+void
 sftk_DestroySession(SFTKSession *session)
 {
     SFTKObjectList *op, *next;
-    PORT_Assert(session->refCount == 0);
 
     /* clean out the attributes */
     /* since no one is referencing us, it's safe to walk the chain
@@ -1844,31 +1842,20 @@ sftk_SessionFromHandle(CK_SESSION_HANDLE handle)
 
     PZ_Lock(lock);
     sftkqueue_find(session, handle, slot->head, slot->sessHashSize);
-    if (session)
-        session->refCount++;
     PZ_Unlock(lock);
 
     return (session);
 }
 
 /*
- * release a reference to a session handle
+ * release a reference to a session handle. This method of using SFTKSessions
+ * is deprecated, but the pattern should be retained until a future effort
+ * to refactor all SFTKSession users at once is completed.
  */
 void
 sftk_FreeSession(SFTKSession *session)
 {
-    PRBool destroy = PR_FALSE;
+    return;
-    SFTKSlot *slot = sftk_SlotFromSession(session);
-    PZLock *lock = SFTK_SESSION_LOCK(slot, session->handle);
-
-    PZ_Lock(lock);
-    if (session->refCount == 1)
-        destroy = PR_TRUE;
-    session->refCount--;
-    PZ_Unlock(lock);
-
-    if (destroy)
-        sftk_DestroySession(session);
 }
 
 void