Ticket #47808 - If be_txn plugin fails in ldbm_back_add, adding entry is double freed.

Bug description: Backend add ldbm_back_add frees the entry to be added,
if the add fails in the be_txn plugins.  But the frontend releases the
entry when an error is returned from the backend.

Fix desxription: When the entry is freed in the backend, set NULL to
the pblock SLAPI_ADD_ENTRY to tell the frontend not to free the entry.

https://fedorahosted.org/389/ticket/47808

Reviewed by [email protected] (Thank you, Mark!!)

ldap/servers/slapd/add.c

@@ -767,10 +767,8 @@ static void op_shared_add (Slapi_PBlock *pb)
 			}
 			else
 			{
-				/* restore e so we can free it below */
-				if (save_e) {
-					e = save_e;
-				}
+				/* PR_ASSERT(!save_e); save_e is supposed to be freed in the backend.  */
+				e = save_e;
 				if (rc == SLAPI_FAIL_DISKFULL)
 				{
 					operation_out_of_disk_space();

ldap/servers/slapd/back-ldbm/ldbm_add.c

@@ -853,7 +853,7 @@ ldbm_back_add( Slapi_PBlock *pb )
 				slapi_pblock_set(pb, SLAPI_PLUGIN_OPRETURN, ldap_result_code ? &ldap_result_code : &retval);
 			}
 			slapi_pblock_get(pb, SLAPI_PB_RESULT_TEXT, &ldap_result_message);
-			LDAPDebug1Arg(LDAP_DEBUG_ANY, "SLAPI_PLUGIN_BE_TXN_PRE_ADD_FN plugin failed: %d",
+			LDAPDebug1Arg(LDAP_DEBUG_ANY, "SLAPI_PLUGIN_BE_TXN_PRE_ADD_FN plugin failed: %d\n",
 			              ldap_result_code ? ldap_result_code : retval);
 			goto error_return;
 		}
@@ -1162,6 +1162,8 @@ error_return:
 		{
 			if (inst) {
 				CACHE_REMOVE(&inst->inst_cache, addingentry);
+				/* tell frontend not to free this entry */
+				slapi_pblock_set(pb, SLAPI_ADD_ENTRY, NULL);
 			}
 		}
 		else