Fix handling of escape sequences in postgres_fdw.application_name

michaelpq · michaelpq · commit 5bace41abc31 · 2023-02-21T20:02:09.000+09:00
postgres_fdw.application_name relies on MyProcPort to define the data that should be added to escape sequences %u (user name) or %d (database name). However this code could be run in processes that lack a MyProcPort, like an autovacuum process, causing crashes. The code generating the application name is made more flexible with this commit, so as it now generates no data for %u and %d if MyProcPort is missing, and a simple "unknown" if MyProcPort exists, but the expected fields are not set. Reported-by: Alexander Lakhin Author: Kyotaro Horiguchi, Michael Paquier Reviewed-by: Hayato Kuroda, Masahiko Sawada Discussion: https://postgr.es/m/17789-8b31c5a4672b74d9@postgresql.org Backpatch-through: 15
diff --git a/contrib/postgres_fdw/option.c b/contrib/postgres_fdw/option.c
@@ -461,8 +461,6 @@ process_pgfdw_appname(const char *appname)
 	const char *p;
 	StringInfoData buf;
 
-	Assert(MyProcPort != NULL);
-
 	initStringInfo(&buf);
 
 	for (p = appname; *p != '\0'; p++)
@@ -498,13 +496,29 @@ process_pgfdw_appname(const char *appname)
 				appendStringInfoString(&buf, cluster_name);
 				break;
 			case 'd':
-				appendStringInfoString(&buf, MyProcPort->database_name);
+				if (MyProcPort)
+				{
+					const char *dbname = MyProcPort->database_name;
+
+					if (dbname)
+						appendStringInfoString(&buf, dbname);
+					else
+						appendStringInfoString(&buf, "[unknown]");
+				}
 				break;
 			case 'p':
 				appendStringInfo(&buf, "%d", MyProcPid);
 				break;
 			case 'u':
-				appendStringInfoString(&buf, MyProcPort->user_name);
+				if (MyProcPort)
+				{
+					const char *username = MyProcPort->user_name;
+
+					if (username)
+						appendStringInfoString(&buf, username);
+					else
+						appendStringInfoString(&buf, "[unknown]");
+				}
 				break;
 			default:
 				/* format error - ignore it */
