Description: setting "backoff-cutoff 0;" in dhclient.conf will cause
 dhclient to divide by zero and crash. It should be handled more
 gracefully.
Author: Kees Cook <kees@ubuntu.com>

--- a/client/dhclient.c
+++ b/client/dhclient.c
@@ -1928,9 +1928,12 @@ void send_discover (cpp)
 			client->interval += random() % (2 * client->interval);
 
 		/* Don't backoff past cutoff. */
-		if (client->interval > client->config->backoff_cutoff)
-			client->interval = (client->config->backoff_cutoff / 2)
-				 + (random() % client->config->backoff_cutoff);
+		if (client->interval > client->config->backoff_cutoff) {
+			client->interval = (client->config->backoff_cutoff / 2);
+			if (client->config->backoff_cutoff)
+				client->interval += (random() %
+					client->config->backoff_cutoff);
+		}
 	} else if (!client->interval)
 		client->interval = client->config->initial_interval;
 
@@ -2177,11 +2180,13 @@ void send_request (cpp)
 
 	/* Don't backoff past cutoff. */
 	if (client -> interval >
-	    client -> config -> backoff_cutoff)
+	    client -> config -> backoff_cutoff) {
 		client -> interval =
-			((client -> config -> backoff_cutoff / 2)
-			 + ((random () >> 2) %
-					client -> config -> backoff_cutoff));
+			(client -> config -> backoff_cutoff / 2);
+		if (client -> config -> backoff_cutoff)
+			client -> interval += ((random () >> 2) %
+				client -> config -> backoff_cutoff);
+	}
 
 	/* If the backoff would take us to the expiry time, just set the
 	   timeout to the expiry time. */