Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.

===================================================================
RCS file: /ftp/cvs/cvsroot/src/sys/sys/socket.h,v
retrieving revision 1.60.2.1
retrieving revision 1.60.2.2
diff -u -p -r1.60.2.1 -r1.60.2.2
--- src/sys/sys/socket.h	2001/08/03 04:14:05	1.60.2.1
+++ src/sys/sys/socket.h	2001/09/13 01:16:28	1.60.2.2
@@ -1,4 +1,4 @@
-/*	$NetBSD: socket.h,v 1.60.2.1 2001/08/03 04:14:05 lukem Exp $	*/
+/*	$NetBSD: socket.h,v 1.60.2.2 2001/09/13 01:16:28 thorpej Exp $	*/
 
 /*
  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
@@ -431,7 +431,14 @@ struct cmsghdr {
 	    (struct cmsghdr *)NULL : \
 	    (struct cmsghdr *)((caddr_t)(cmsg) + __CMSG_ALIGN((cmsg)->cmsg_len)))
 
-#define	CMSG_FIRSTHDR(mhdr)	((struct cmsghdr *)(mhdr)->msg_control)
+/*
+ * RFC 2292 requires to check msg_controllen, in case that the kernel returns
+ * an empty list for some reasons.
+ */
+#define	CMSG_FIRSTHDR(mhdr) \
+	((mhdr)->msg_controllen >= sizeof(struct cmsghdr) ? \
+	 (struct cmsghdr *)(mhdr)->msg_control : \
+	 (struct cmsghdr *)NULL)
 
 #define CMSG_SPACE(l)	(__CMSG_ALIGN(sizeof(struct cmsghdr)) + __CMSG_ALIGN(l))
 #define CMSG_LEN(l)	(__CMSG_ALIGN(sizeof(struct cmsghdr)) + (l))