make udhcpc use /dev/urandom

ChangeLog

@@ -1,4 +1,5 @@
 0.9.8 (pending)
++ use /dev/urandom to seed xid's (instead of time(0)) 
 + fixed renew behavior (me)
 + udhcp now fits nicely into busybox
   (Glenn McGrath <bug1@optushome.com.au> as well as myself)

README

@@ -147,6 +147,17 @@ The paramaters for enviromental variables are as follows:
 
 additional options are easily added in options.c.
 	
+udhcpc will seed its random number generator (used for generating xid's)
+by reading /dev/urandom. If you have a lot of embedded systems on the same
+network, with no entropy, you can either seed /dev/urandom by a method of
+your own, or doing the following on startup:
+
+ifconfig eth0 > /dev/urandom
+
+in order to seed /dev/urandom with some data (mac address) unique to your
+system. If reading /dev/urandom fails, udhcpc will fall back to its old
+behavior of seeding with time(0).
+
 udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,
 and SIGUSR2 will force a release of the current lease, and cause udhcpc to
 go into an inactive state (until it is killed, or receives a SIGUSR1). You do

TODO

@@ -1,17 +1,13 @@
 TODO
 ----
++ using time(0) breaks if the system clock changes, find a portable solution
 + make failure of reading functions revert to previous value, not the default
 + sanity code for option[OPT_LEN]
 + fix aliasing (ie: eth0:0)
-+ DONE: Make sure get_raw_packet only accepts packets on the specified interface
 + better standard linux distro support
-+ DONE: make config file a command line option for server
-+ IMPLEMENTED: make forking a command line option
 + make sure packet generation works on a wide varitey of arches
 + Interoperability testing
 + Hooks within the DHCP server
 + Additional bootp support in client/server
 + Make serverid option in server configurable
-+ DONE: cause client to generate DHCP_VENDOR option
 + Possibly add failure message to DHCP NAK
-+ Possibly log DHCP NAK failure message in client

clientpacket.c

@@ -35,6 +35,10 @@
 #include <unistd.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 
 
 #include "dhcpd.h"
@@ -49,7 +53,17 @@ unsigned long random_xid(void)
 {
 	static int initialized;
 	if (!initialized) {
-		srand(time(0));
+		int fd;
+		unsigned long seed;
+
+		fd = open("/dev/urandom", 0);
+		if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
+			LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %s",
+				strerror(errno));
+			seed = time(0);
+		}
+		if (fd >= 0) close(fd);
+		srand(seed);
 		initialized++;
 	}
 	return rand();