--- a/src/lib/fdpass.c	Sun Apr 06 00:15:01 2003 +0300
+++ b/src/lib/fdpass.c	Tue Apr 08 16:12:47 2003 +0300
@@ -1,7 +1,15 @@
 /*
- fdpass.c - FD passing
+ fdpass.c - File descriptor passing between processes via UNIX sockets
+
+ This isn't fully portable, but pretty much all UNIXes nowadays should
+ support this. If you're having runtime problems, check the end of fd_read()
+ and play with the if condition.
 
-    Copyright (c) 2002 Timo Sirainen
+ If this file doesn't compile at all, you should check if this is supported
+ in your system at all. It may require some extra #define to enable it.
+ If not, you're pretty much out of luck. Cygwin didn't last I checked.
+
+    Copyright (c) 2002-2003 Timo Sirainen
 
     Permission is hereby granted, free of charge, to any person obtaining
     a copy of this software and associated documentation files (the
@@ -107,9 +115,18 @@
 		return ret;
 	}
 
-	/* at least one byte transferred - we should have the fd now */
+	/* at least one byte transferred - we should have the fd now.
+	   do extra checks to make sure it really is an fd that is being
+	   transferred to avoid potential DoS conditions. some systems don't
+	   set all these values correctly however:
+
+	   Linux 2.0.x - cmsg_len, cmsg_level, cmsg_type are not set
+	   Tru64 - msg_controllen isn't set */
 	cmsg = CMSG_FIRSTHDR(&msg);
-	if (msg.msg_controllen < CMSG_SPACE(sizeof(int)) ||
+	if (
+#ifndef __osf__
+	    msg.msg_controllen < CMSG_SPACE(sizeof(int)) ||
+#endif
 	    cmsg == NULL || cmsg->cmsg_len < CMSG_LEN(sizeof(int)) ||
 	    cmsg->cmsg_level != SOL_SOCKET || cmsg->cmsg_type != SCM_RIGHTS)
 		*fd = -1;

--- a/src/master/login-process.c	Sun Apr 06 00:15:01 2003 +0300
+++ b/src/master/login-process.c	Tue Apr 08 16:12:47 2003 +0300
@@ -138,7 +138,8 @@
 {
 	if (!p->listening) {
 		i_error("login: received another \"not listening\" "
-			"notification");
+			"notification (if you can't login at all, "
+			"see src/lib/fdpass.c)");
 		return;
 	}