Fix DHCP lease time parsing.

Currently we treat a lease time larger than 2**31-1 as a negative
value, which causes DhcpClient to attempt to renew its IP address
constantly. Fix this by properly handling large and infinite
lifetimes, and while we're at it, impose a minimum lease time of
60 seconds.

Bug: 21352084
Change-Id: If62c9efeffad6222e2fe0c110f77d0e4c70de96d

2 files changed, 38 insertions, 12 deletions

diff --git a/services/net/java/android/net/dhcp/DhcpClient.java b/services/net/java/android/net/dhcp/DhcpClient.java
index e1d1787..1ee34cc 100644
--- a/services/net/java/android/net/dhcp/DhcpClient.java
+++ b/services/net/java/android/net/dhcp/DhcpClient.java
@@ -390,11 +390,15 @@ public class DhcpClient extends BaseDhcpStateMachine {
     }
 
     private void scheduleRenew() {
-        long now = SystemClock.elapsedRealtime();
-        long alarmTime = (now + mDhcpLeaseExpiry) / 2;
         mAlarmManager.cancel(mRenewIntent);
-        mAlarmManager.setExact(AlarmManager.ELAPSED_REALTIME_WAKEUP, alarmTime, mRenewIntent);
-        Log.d(TAG, "Scheduling renewal in " + ((alarmTime - now) / 1000) + "s");
+        if (mDhcpLeaseExpiry != 0) {
+            long now = SystemClock.elapsedRealtime();
+            long alarmTime = (now + mDhcpLeaseExpiry) / 2;
+            mAlarmManager.setExact(AlarmManager.ELAPSED_REALTIME_WAKEUP, alarmTime, mRenewIntent);
+            Log.d(TAG, "Scheduling renewal in " + ((alarmTime - now) / 1000) + "s");
+        } else {
+            Log.d(TAG, "Infinite lease, no renewal needed");
+        }
     }
 
     private void notifyLease() {
@@ -586,6 +590,12 @@ public class DhcpClient extends BaseDhcpStateMachine {
         return true;
     }
 
+    public void setDhcpLeaseExpiry(DhcpPacket packet) {
+        long leaseTimeMillis = packet.getLeaseTimeMillis();
+        mDhcpLeaseExpiry =
+                (leaseTimeMillis > 0) ? SystemClock.elapsedRealtime() + leaseTimeMillis : 0;
+    }
+
     /**
      * Retransmits packets using jittered exponential backoff with an optional timeout. Packet
      * transmission is triggered by CMD_KICK, which is sent by an AlarmManager alarm.
@@ -723,10 +733,9 @@ public class DhcpClient extends BaseDhcpStateMachine {
                 DhcpResults results = packet.toDhcpResults();
                 if (results != null) {
                     mDhcpLease = results;
-                    Log.d(TAG, "Confirmed lease: " + mDhcpLease);
-                    mDhcpLeaseExpiry = SystemClock.elapsedRealtime() +
-                            mDhcpLease.leaseDuration * 1000;
                     mOffer = null;
+                    Log.d(TAG, "Confirmed lease: " + mDhcpLease);
+                    setDhcpLeaseExpiry(packet);
                     transitionTo(mDhcpBoundState);
                 }
             } else if (packet instanceof DhcpNakPacket) {
@@ -797,10 +806,7 @@ public class DhcpClient extends BaseDhcpStateMachine {
         protected void receivePacket(DhcpPacket packet) {
             if (!isValidPacket(packet)) return;
             if ((packet instanceof DhcpAckPacket)) {
-                DhcpResults results = packet.toDhcpResults();
-                mDhcpLease.leaseDuration = results.leaseDuration;
-                mDhcpLeaseExpiry = SystemClock.elapsedRealtime() +
-                        mDhcpLease.leaseDuration * 1000;
+                setDhcpLeaseExpiry(packet);
                 transitionTo(mDhcpBoundState);
             } else if (packet instanceof DhcpNakPacket) {
                 transitionTo(mDhcpInitState);
diff --git a/services/net/java/android/net/dhcp/DhcpPacket.java b/services/net/java/android/net/dhcp/DhcpPacket.java
index b923b1b..2a25d30 100644
--- a/services/net/java/android/net/dhcp/DhcpPacket.java
+++ b/services/net/java/android/net/dhcp/DhcpPacket.java
@@ -28,6 +28,12 @@ import java.util.List;
 abstract class DhcpPacket {
     protected static final String TAG = "DhcpPacket";
 
+    // dhcpcd has a minimum lease of 20 seconds, but DhcpStateMachine would refuse to wake up the
+    // CPU for anything shorter than 5 minutes. For sanity's sake, this must be higher than the
+    // DHCP client timeout.
+    public static final int MINIMUM_LEASE = 60;
+    public static final int INFINITE_LEASE = (int) 0xffffffff;
+
     public static final Inet4Address INADDR_ANY = (Inet4Address) Inet4Address.ANY;
     public static final Inet4Address INADDR_BROADCAST = (Inet4Address) Inet4Address.ALL;
     public static final byte[] ETHER_BROADCAST = new byte[] {
@@ -1006,11 +1012,25 @@ abstract class DhcpPacket {
         results.domains = mDomainName;
         results.serverAddress = mServerIdentifier;
         results.vendorInfo = mVendorId;
-        results.leaseDuration = mLeaseTime;
+        results.leaseDuration = (mLeaseTime != null) ? mLeaseTime : INFINITE_LEASE;
         return results;
     }
 
     /**
+     * Returns the parsed lease time, in milliseconds, or 0 for infinite.
+     */
+    public long getLeaseTimeMillis() {
+        // dhcpcd treats the lack of a lease time option as an infinite lease.
+        if (mLeaseTime == null || mLeaseTime == INFINITE_LEASE) {
+            return 0;
+        } else if (0 <= mLeaseTime && mLeaseTime < MINIMUM_LEASE) {
+            return MINIMUM_LEASE * 1000;
+        } else {
+            return (mLeaseTime & 0xffffffffL) * 1000;
+        }
+    }
+
+    /**
      * Builds a DHCP-DISCOVER packet from the required specified
      * parameters.
      */