Add check for malloc failure in libpq calls

The functions `PQconndefaults` and `PQmakeEmptyPGresult` calls
`malloc` and can return NULL if it fails to allocate memory for the
defaults and the empty result. It is checked with an `Assert`, but this
will be removed in production builds.

Replace the `Assert` with an checks to generate an error in production
builds rather than trying to de-reference the pointer and cause a
crash.

CHANGELOG.md

@@ -19,6 +19,7 @@ accidentally triggering the load of a previous DB version.**
 * #5233 Out of on_proc_exit slots on guc license change
 * #5427 Handle user-defined FDW options properly
 * #5442 Decompression may have lost DEFAULT values
+* #5446 Add checks for malloc failure in libpq calls
 
 **Thanks**
 * @nikolaps for reporting an issue with the COPY fetcher

src/utils.h

@@ -40,6 +40,14 @@
 /* find the length of a statically sized array */
 #define TS_ARRAY_LEN(array) (sizeof(array) / sizeof(*array))
 
+/* Use condition to check if out of memory */
+#define TS_OOM_CHECK(COND, FMT, ...)                                                               \
+	do                                                                                             \
+	{                                                                                              \
+		if (!(COND))                                                                               \
+			ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg(FMT, ##__VA_ARGS__)));          \
+	} while (0)
+
 extern TSDLLEXPORT bool ts_type_is_int8_binary_compatible(Oid sourcetype);
 
 typedef enum TimevalInfinity

tsl/src/remote/connection.c

@@ -546,7 +546,7 @@ unset_libpq_envvar(void)
 	PQconninfoOption *lopt;
 	PQconninfoOption *options = PQconndefaults();
 
-	Assert(options != NULL);
+	TS_OOM_CHECK(options, "out of memory");
 
 	/* Explicitly unset all libpq environment variables.
 	 *
@@ -1024,6 +1024,7 @@ remote_connection_get_result(const TSConnection *conn, TimestampTz endtime)
 				if (PQconsumeInput(conn->pg_conn) == 0)
 				{
 					pgres = PQmakeEmptyPGresult(conn->pg_conn, PGRES_FATAL_ERROR);
+					TS_OOM_CHECK(pgres, "out of memory");
 					PQfireResultCreateEvents(conn->pg_conn, pgres);
 					return pgres;
 				}
@@ -1102,6 +1103,7 @@ remote_connection_exec_timeout(TSConnection *conn, const char *cmd, TimestampTz
 			if (ret == 0)
 			{
 				res = PQmakeEmptyPGresult(conn->pg_conn, PGRES_FATAL_ERROR);
+				TS_OOM_CHECK(res, "out of memory");
 				PQfireResultCreateEvents(conn->pg_conn, res);
 				return res;
 			}
@@ -2522,7 +2524,6 @@ remote_connection_end_copy(TSConnection *conn, TSConnectionError *err)
 		}
 	}
 
-	Assert(res == NULL);
 	remote_connection_set_status(conn, CONN_IDLE);
 
 	return success;