correct non-repetitive ID code, based on comments from niels provos.

- seed2 is necessary, but use it as "seed2 + x" not "seed2 ^ x".
- skipping number is not needed, so disable it for 16bit generator (makes
  the repetition period to 30000)

2 files changed, 9 insertions, 8 deletions

diff --git a/sys/netinet/ip_id.c b/sys/netinet/ip_id.c
index 0534d406e33..67208b89de9 100644
--- a/sys/netinet/ip_id.c
+++ b/sys/netinet/ip_id.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ip_id.c,v 1.7 2003/09/21 04:06:39 itojun Exp $ */
+/* $OpenBSD: ip_id.c,v 1.8 2003/12/10 07:21:00 itojun Exp $ */
 
 /*
  * Copyright 1998 Niels Provos <provos@citi.umich.edu>
@@ -174,10 +174,14 @@ ip_randomid(void)
 	if (!tmp)
 		tmp = arc4random();
 
+#if 0
 	/* Skip a random number of ids */
 	n = tmp & 0x3; tmp = tmp >> 2;
 	if (ru_counter + n >= RU_MAX)
 		ip_initid();
+#else
+	n = 0;
+#endif
 
 	for (i = 0; i <= n; i++)
 		/* Linear Congruential Generator */
@@ -185,5 +189,5 @@ ip_randomid(void)
 
 	ru_counter += i;
 
-	return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) | ru_msb;
+	return (ru_seed ^ pmod(ru_g,ru_seed2 + ru_x, RU_N)) | ru_msb;
 }
diff --git a/sys/netinet6/ip6_id.c b/sys/netinet6/ip6_id.c
index e509a6364a6..5b6151a246a 100644
--- a/sys/netinet6/ip6_id.c
+++ b/sys/netinet6/ip6_id.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip6_id.c,v 1.1 2003/10/01 21:41:05 itojun Exp $	*/
+/*	$OpenBSD: ip6_id.c,v 1.2 2003/12/10 07:21:01 itojun Exp $	*/
 /*	$NetBSD: ip6_id.c,v 1.7 2003/09/13 21:32:59 itojun Exp $	*/
 /*	$KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun Exp $	*/
 
@@ -223,15 +223,12 @@ static u_int32_t
 randomid(struct randomtab *p)
 {
 	int i, n;
-	u_int32_t tmp;
 
 	if (p->ru_counter >= p->ru_max || time.tv_sec > p->ru_reseed)
 		initid(p);
 
-	tmp = arc4random();
-
 	/* Skip a random number of ids */
-	n = tmp & 0x3; tmp = tmp >> 2;
+	n = arc4random() & 0x3;
 	if (p->ru_counter + n >= p->ru_max)
 		initid(p);
 
@@ -242,7 +239,7 @@ randomid(struct randomtab *p)
 
 	p->ru_counter += i;
 
-	return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) |
+	return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
 	    p->ru_msb;
 }