Abort authentication if the client selected an invalid SASL mechanism.

Previously, the server would log an error, but then try to continue with
SCRAM-SHA-256 anyway.

Michael Paquier

Discussion: https://www.postgresql.org/message-id/CAB7nPqR0G5aF2_kc_LH29knVqwvmBc66TF5DicvpGVdke68nKw@mail.gmail.com

src/backend/libpq/auth.c

@@ -934,9 +934,13 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
 			 */
 			selected_mech = pq_getmsgrawstring(&buf);
 			if (strcmp(selected_mech, SCRAM_SHA256_NAME) != 0)
+			{
 				ereport(COMMERROR,
 						(errcode(ERRCODE_PROTOCOL_VIOLATION),
 						 errmsg("client selected an invalid SASL authentication mechanism")));
+				pfree(buf.data);
+				return STATUS_ERROR;
+			}
 
 			inputlen = pq_getmsgint(&buf, 4);
 			if (inputlen == -1)