Fix handling of escape sequences in postgres_fdw.application_name

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
index 984e4d168a03640bd2abec63e3bebc7c49493ae8..d530f7d0860aea641388dc8782e9cc4a12e0efcc 100644 (file)
--- a/contrib/postgres_fdw/option.c
+++ b/contrib/postgres_fdw/option.c
@@ -485,8 +485,6 @@ process_pgfdw_appname(const char *appname)
    const char *p;
    StringInfoData buf;
 
-   Assert(MyProcPort != NULL);
-
    initStringInfo(&buf);
 
    for (p = appname; *p != '\0'; p++)
@@ -522,13 +520,29 @@ 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 */