From 8672529b37fc73fbcc15cb2b2ba9b677f37dac5e Mon Sep 17 00:00:00 2001
From: Holger Weiss <holger@zedat.fu-berlin.de>
Date: Fri, 16 Sep 2016 09:43:04 +0200
Subject: check_dhcp: Make xid a bit more random

Don't just use the current time(2) to seed the PRNG that generates the
xid.  A DHCP server might be checked multiple times per second.

diff --git a/plugins-root/check_dhcp.c b/plugins-root/check_dhcp.c
index 445ddbc..88b7ca1 100644
--- a/plugins-root/check_dhcp.c
+++ b/plugins-root/check_dhcp.c
@@ -463,10 +463,9 @@ int send_dhcp_discover(int sock){
 	discover_packet.hlen=ETHERNET_HARDWARE_ADDRESS_LENGTH;
 
 	/*
-	 * transaction ID is supposed to be random.  We won't use the address so
-	 * we don't care about high entropy here.  time(2) is good enough.
+	 * transaction ID is supposed to be random.
 	 */
-	srand(time(NULL));
+	srand(time(NULL)^getpid());
 	packet_xid=random();
 	discover_packet.xid=htonl(packet_xid);
 
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