Merge "Gracefully handle integer overflows." am: cdb1f03144 am: fe6c5793ce

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1316217

Change-Id: I0bba17d0367ebf4e1c868a8cc7471366bc7a4408

core/java/android/net/NetworkUtils.java

@@ -477,4 +477,35 @@ public class NetworkUtils {
 
         return true;
     }
+
+    /**
+     * Safely multiple a value by a rational.
+     * <p>
+     * Internally it uses integer-based math whenever possible, but switches
+     * over to double-based math if values would overflow.
+     * @hide
+     */
+    public static long multiplySafeByRational(long value, long num, long den) {
+        if (den == 0) {
+            throw new ArithmeticException("Invalid Denominator");
+        }
+        long x = value;
+        long y = num;
+
+        // Logic shamelessly borrowed from Math.multiplyExact()
+        long r = x * y;
+        long ax = Math.abs(x);
+        long ay = Math.abs(y);
+        if (((ax | ay) >>> 31 != 0)) {
+            // Some bits greater than 2^31 that might cause overflow
+            // Check the result using the divide operator
+            // and check for the special case of Long.MIN_VALUE * -1
+            if (((y != 0) && (r / y != x)) ||
+                    (x == Long.MIN_VALUE && y == -1)) {
+                // Use double math to avoid overflowing
+                return (long) (((double) num / den) * value);
+            }
+        }
+        return r / den;
+    }
 }

tests/net/java/com/android/server/net/NetworkStatsCollectionTest.java

@@ -23,11 +23,12 @@ import static android.net.NetworkStats.TAG_NONE;
 import static android.net.NetworkStats.UID_ALL;
 import static android.net.NetworkStatsHistory.FIELD_ALL;
 import static android.net.NetworkTemplate.buildTemplateMobileAll;
+import static android.net.NetworkUtils.multiplySafeByRational;
 import static android.os.Process.myUid;
 import static android.text.format.DateUtils.HOUR_IN_MILLIS;
 import static android.text.format.DateUtils.MINUTE_IN_MILLIS;
 
-import static com.android.server.net.NetworkStatsCollection.multiplySafe;
+import static com.android.testutils.MiscAssertsKt.assertThrows;
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
@@ -505,23 +506,25 @@ public class NetworkStatsCollectionTest {
     }
 
     @Test
-    public void testMultiplySafe() {
+    public void testMultiplySafeRational() {
-        assertEquals(25, multiplySafe(50, 1, 2));
+        assertEquals(25, multiplySafeByRational(50, 1, 2));
-        assertEquals(100, multiplySafe(50, 2, 1));
+        assertEquals(100, multiplySafeByRational(50, 2, 1));
 
-        assertEquals(-10, multiplySafe(30, -1, 3));
+        assertEquals(-10, multiplySafeByRational(30, -1, 3));
-        assertEquals(0, multiplySafe(30, 0, 3));
+        assertEquals(0, multiplySafeByRational(30, 0, 3));
-        assertEquals(10, multiplySafe(30, 1, 3));
+        assertEquals(10, multiplySafeByRational(30, 1, 3));
-        assertEquals(20, multiplySafe(30, 2, 3));
+        assertEquals(20, multiplySafeByRational(30, 2, 3));
-        assertEquals(30, multiplySafe(30, 3, 3));
+        assertEquals(30, multiplySafeByRational(30, 3, 3));
-        assertEquals(40, multiplySafe(30, 4, 3));
+        assertEquals(40, multiplySafeByRational(30, 4, 3));
 
         assertEquals(100_000_000_000L,
-                multiplySafe(300_000_000_000L, 10_000_000_000L, 30_000_000_000L));
+                multiplySafeByRational(300_000_000_000L, 10_000_000_000L, 30_000_000_000L));
         assertEquals(100_000_000_010L,
-                multiplySafe(300_000_000_000L, 10_000_000_001L, 30_000_000_000L));
+                multiplySafeByRational(300_000_000_000L, 10_000_000_001L, 30_000_000_000L));
         assertEquals(823_202_048L,
-                multiplySafe(4_939_212_288L, 2_121_815_528L, 12_730_893_165L));
+                multiplySafeByRational(4_939_212_288L, 2_121_815_528L, 12_730_893_165L));
+
+        assertThrows(ArithmeticException.class, () -> multiplySafeByRational(30, 3, 0));
     }
 
     /**