Gracefully handle integer overflows.
Avoid recording negative data by doing integer-based
math as much as possible, but switch to double-based
math if we detect that we'd end up causing an overflow.
Test :
- Builds, Boots
- High data throughput scenarios
- NetworkStatsHistoryTest, NetworkStatsCollectionTest,
NetworkStatsTest
Bug: 119527458
Change-Id: I55d4aa649bea3ae201ad513074ff2b71cb918dad
diff --git a/core/java/android/net/NetworkUtils.java b/core/java/android/net/NetworkUtils.java
index 0b92b95..1e004e4 100644
--- a/core/java/android/net/NetworkUtils.java
+++ b/core/java/android/net/NetworkUtils.java
@@ -476,4 +476,35 @@
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;
+ }
}
diff --git a/tests/net/java/com/android/server/net/NetworkStatsCollectionTest.java b/tests/net/java/com/android/server/net/NetworkStatsCollectionTest.java
index 551498f..e83d2a9 100644
--- a/tests/net/java/com/android/server/net/NetworkStatsCollectionTest.java
+++ b/tests/net/java/com/android/server/net/NetworkStatsCollectionTest.java
@@ -23,11 +23,12 @@
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 @@
}
@Test
- public void testMultiplySafe() {
- assertEquals(25, multiplySafe(50, 1, 2));
- assertEquals(100, multiplySafe(50, 2, 1));
+ public void testMultiplySafeRational() {
+ assertEquals(25, multiplySafeByRational(50, 1, 2));
+ assertEquals(100, multiplySafeByRational(50, 2, 1));
- assertEquals(-10, multiplySafe(30, -1, 3));
- assertEquals(0, multiplySafe(30, 0, 3));
- assertEquals(10, multiplySafe(30, 1, 3));
- assertEquals(20, multiplySafe(30, 2, 3));
- assertEquals(30, multiplySafe(30, 3, 3));
- assertEquals(40, multiplySafe(30, 4, 3));
+ assertEquals(-10, multiplySafeByRational(30, -1, 3));
+ assertEquals(0, multiplySafeByRational(30, 0, 3));
+ assertEquals(10, multiplySafeByRational(30, 1, 3));
+ assertEquals(20, multiplySafeByRational(30, 2, 3));
+ assertEquals(30, multiplySafeByRational(30, 3, 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));
}
/**
