svn commit: r317915 - head/sbin/dhclient

[Nick Hibma]

Author: n_hibma
Date: Sun May  7 19:59:37 2017
New Revision: 317915
URL: https://svnweb.freebsd.org/changeset/base/317915

Log:
  Fix handling of large DHCP expiry values.
  
  They would overflow a signed 32-bit time_t on 32 bit architectures. This
  was taken care of, but a compiler optimisation makes this behave
  erratically. This could be resolved by adding a -fwrapv flag, but
  instead we can check the value before adding the current timestamp to
  it.
  
  In the lease file values are still wrong though:
  
    option dhcp-rebinding-time -644245096;
  
  PR:		218980
  Reported by:	Bob Eager
  MFC after:	2 weeks

Modified:
  head/sbin/dhclient/dhclient.c

Modified: head/sbin/dhclient/dhclient.c
==============================================================================
--- head/sbin/dhclient/dhclient.c	Sun May  7 19:57:45 2017	(r317914)
+++ head/sbin/dhclient/dhclient.c	Sun May  7 19:59:37 2017	(r317915)
@@ -108,7 +108,11 @@ struct pidfh *pidfile;
  */
 #define ASSERT_STATE(state_is, state_shouldbe) {}
 
-#define TIME_MAX 2147483647
+/*
+ * We need to check that the expiry, renewal and rebind times are not beyond
+ * the end of time (~2038 when a 32-bit time_t is being used).
+ */
+#define TIME_MAX        ((((time_t) 1 << (sizeof(time_t) * CHAR_BIT - 2)) - 1) * 2 + 1)
 
 int		log_priority;
 int		no_daemon;
@@ -766,15 +770,17 @@ dhcpack(struct packet *packet)
 	else
 		ip->client->new->expiry = default_lease_time;
 	/* A number that looks negative here is really just very large,
-	   because the lease expiry offset is unsigned. */
-	if (ip->client->new->expiry < 0)
-		ip->client->new->expiry = TIME_MAX;
+	   because the lease expiry offset is unsigned. Also make sure that
+           the addition of cur_time below does not overflow (a 32 bit) time_t. */
+	if (ip->client->new->expiry < 0 ||
+            ip->client->new->expiry > TIME_MAX - cur_time)
+		ip->client->new->expiry = TIME_MAX - cur_time;
 	/* XXX should be fixed by resetting the client state */
 	if (ip->client->new->expiry < 60)
 		ip->client->new->expiry = 60;
 
         /* Unless overridden in the config, take the server-provided renewal
-         * time if there is one; otherwise figure it out according to the spec.
+         * time if there is one. Otherwise figure it out according to the spec.
          * Also make sure the renewal time does not exceed the expiry time.
          */
         if (ip->client->config->default_actions[DHO_DHCP_RENEWAL_TIME] ==
@@ -786,7 +792,8 @@ dhcpack(struct packet *packet)
 		    ip->client->new->options[DHO_DHCP_RENEWAL_TIME].data);
 	else
 		ip->client->new->renewal = ip->client->new->expiry / 2;
-        if (ip->client->new->renewal > ip->client->new->expiry / 2)
+        if (ip->client->new->renewal < 0 ||
+            ip->client->new->renewal > ip->client->new->expiry / 2)
                 ip->client->new->renewal = ip->client->new->expiry / 2;
 
 	/* Same deal with the rebind time. */
@@ -798,20 +805,15 @@ dhcpack(struct packet *packet)
 		ip->client->new->rebind = getULong(
 		    ip->client->new->options[DHO_DHCP_REBINDING_TIME].data);
 	else
-		ip->client->new->rebind = ip->client->new->renewal * 7 / 4;
-        if (ip->client->new->rebind > ip->client->new->renewal * 7 / 4)
-                ip->client->new->rebind = ip->client->new->renewal * 7 / 4;
-
-	ip->client->new->expiry += cur_time;
-	/* Lease lengths can never be negative. */
-	if (ip->client->new->expiry < cur_time)
-		ip->client->new->expiry = TIME_MAX;
-	ip->client->new->renewal += cur_time;
-	if (ip->client->new->renewal < cur_time)
-		ip->client->new->renewal = TIME_MAX;
-	ip->client->new->rebind += cur_time;
-	if (ip->client->new->rebind < cur_time)
-		ip->client->new->rebind = TIME_MAX;
+		ip->client->new->rebind = ip->client->new->renewal / 4 * 7;
+	if (ip->client->new->rebind < 0 ||
+            ip->client->new->rebind > ip->client->new->renewal / 4 * 7)
+                ip->client->new->rebind = ip->client->new->renewal / 4 * 7;
+
+        /* Convert the time offsets into seconds-since-the-epoch */
+        ip->client->new->expiry += cur_time;
+        ip->client->new->renewal += cur_time;
+        ip->client->new->rebind += cur_time;
 
 	bind_lease(ip);
 }