diff options
Diffstat (limited to 'sys')
| -rw-r--r-- | sys/netinet/ip_id.c | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/sys/netinet/ip_id.c b/sys/netinet/ip_id.c index 07834dfcd25..1a4b8a1b740 100644 --- a/sys/netinet/ip_id.c +++ b/sys/netinet/ip_id.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ip_id.c,v 1.18 2008/03/02 21:38:18 deraadt Exp $ */ +/* $OpenBSD: ip_id.c,v 1.19 2008/03/15 04:36:31 djm Exp $ */ /* * Copyright (c) 2008 Theo de Raadt, Ryan McBride @@ -51,17 +51,18 @@ ip_randomid(void) ipid_initialized = 1; /* - * Initialize using a Durstenfeld shuffle. Even if our PRNG - * is imperfect at boot time, we have deferred doing this until - * the first packet being sent and now must generate an ID. + * Initialize with a random permutation. Do so using Knuth + * which avoids the exchange in the Durstenfeld shuffle. + * (See "The Art of Computer Programming, Vol 2" 3rd ed, pg. 145). + * + * Even if our PRNG is imperfect at boot time, we have deferred + * doing this until the first packet being sent and now must + * generate an ID. */ - for (i = 0; i < sizeof(ip_shuffle)/sizeof(ip_shuffle[0]); ++i) - ip_shuffle[i] = i; - for (i = sizeof(ip_shuffle)/sizeof(ip_shuffle[0]); --i; ) { + for (i = 0; i < sizeof(ip_shuffle)/sizeof(ip_shuffle[0]); ++i) { i2 = arc4random_uniform(i + 1); - r = ip_shuffle[i]; ip_shuffle[i] = ip_shuffle[i2]; - ip_shuffle[i2] = r; + ip_shuffle[i2] = i; } } |