From a92cb1c4c67cc46c1576afff5c917760f35f19a3 Mon Sep 17 00:00:00 2001
From: "Nicholas J. Kain" <nicholas@kain.us>
Date: Wed, 6 Jul 2011 08:46:05 -0400
Subject: [PATCH] Randomize the DHCP timeout by +[0,1000]ms to comply with RFC.

---
 ndhc/arp.c   | 8 ++++----
 ndhc/state.c | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/ndhc/arp.c b/ndhc/arp.c
index 881c837..e638469 100644
--- a/ndhc/arp.c
+++ b/ndhc/arp.c
@@ -1,5 +1,5 @@
 /* arp.c - arp ping checking
- * Time-stamp: <2011-07-05 16:00:42 njk>
+ * Time-stamp: <2011-07-06 08:41:06 njk>
  *
  * Copyright 2010-2011 Nicholas J. Kain <njkain@gmail.com>
  *
@@ -123,7 +123,7 @@ static void arp_set_bpf_basic(int fd)
         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (ETH_P_IP << 16) | 0x0604, 1, 0),
         BPF_STMT(BPF_RET + BPF_K, 0),
         // Sanity tests passed, so send all possible data.
-        BPF_STMT(BPF_RET + BPF_K, 0x0fffffff),
+        BPF_STMT(BPF_RET + BPF_K, 0x7fffffff),
     };
     static const struct sock_fprog sfp_arp = {
         .len = sizeof sf_arp / sizeof sf_arp[0],
@@ -164,13 +164,13 @@ static void arp_set_bpf_defense(struct client_state_t *cs, int fd)
         // be passed along.
         BPF_STMT(BPF_LD + BPF_W + BPF_ABS, 22),
         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, mac4b, 1, 0),
-        BPF_STMT(BPF_RET + BPF_K, 0x0fffffff),
+        BPF_STMT(BPF_RET + BPF_K, 0x7fffffff),
         // If the last two bytes of the ARP packet source hardware address
         // do not equal our hardware address, then it's a conflict and should
         // be passed along.
         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 26),
         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, mac2b, 1, 0),
-        BPF_STMT(BPF_RET + BPF_K, 0x0fffffff),
+        BPF_STMT(BPF_RET + BPF_K, 0x7fffffff),
         // Packet announces our IP address and hardware address, so it requires
         // no action.
         BPF_STMT(BPF_RET + BPF_K, 0),
diff --git a/ndhc/state.c b/ndhc/state.c
index 6caf83d..f074bd9 100644
--- a/ndhc/state.c
+++ b/ndhc/state.c
@@ -56,7 +56,7 @@ static int delay_timeout(int numpackets)
     char tot[] = { 4, 8, 16, 32, 64 };
     if (numpackets < sizeof tot)
         to = tot[numpackets];
-    return to * 1000;
+    return to * 1000 + rand() % 1000;
 }
 
 void reinit_selecting(struct client_state_t *cs, int timeout)
@@ -192,7 +192,7 @@ static void an_packet(struct client_state_t *cs, struct dhcpmsg *packet,
         } else {
             memcpy(&cs->lease, temp, 4);
             cs->lease = ntohl(cs->lease);
-            cs->lease &= 0x0fffffff;
+            cs->lease &= 0x7fffffff;
             if (cs->lease < 60) {
                 log_warning("Server sent lease of <1m.  Forcing lease to 1m.");
                 cs->lease = 60;