LineageOS/android_packages_modules_Connectivity
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Gracefully handle integer overflows.

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Try sticking with integer-based math as much as possible for speed,
but switch to double-based math if we detect that we'd end up
causing an overflow.

New tests to verify.

Test: bit FrameworksNetTests:com.android.server.net.NetworkStatsCollectionTest
Bug: 65257769
Change-Id: I1ae35599be134f81850c0a3d86928b057fba1eff
This commit is contained in:
Jeff Sharkey
2017-09-01 12:51:51 -06:00
parent 2f0f8f418f
commit 121a1fcbb2
1 changed files with 32 additions and 4 deletions
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36
services/core/java/com/android/server/net/NetworkStatsCollection.java
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@@ -177,6 +177,34 @@ public class NetworkStatsCollection implements FileRotator.Reader {
}
}
/**
* 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.
*/
@VisibleForTesting
public static long multiplySafe(long value, long num, long den) {
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;
}
public int[] getRelevantUids(@NetworkStatsAccess.Level int accessLevel) {
return getRelevantUids(accessLevel, Binder.getCallingUid());
}
@@ -274,8 +302,8 @@ public class NetworkStatsCollection implements FileRotator.Reader {
final long rawRxBytes = entry.rxBytes;
final long rawTxBytes = entry.txBytes;
final long targetBytes = augmentPlan.getDataUsageBytes();
final long targetRxBytes = (rawRxBytes * targetBytes) / rawBytes;
final long targetTxBytes = (rawTxBytes * targetBytes) / rawBytes;
final long targetRxBytes = multiplySafe(targetBytes, rawRxBytes, rawBytes);
final long targetTxBytes = multiplySafe(targetBytes, rawTxBytes, rawBytes);
// Scale all matching buckets to reach anchor target
final long beforeTotal = combined.getTotalBytes();
@@ -283,8 +311,8 @@ public class NetworkStatsCollection implements FileRotator.Reader {
combined.getValues(i, entry);
if (entry.bucketStart >= augmentStart
&& entry.bucketStart + entry.bucketDuration <= augmentEnd) {
entry.rxBytes = (entry.rxBytes * targetRxBytes) / rawRxBytes;
entry.txBytes = (entry.txBytes * targetTxBytes) / rawTxBytes;
entry.rxBytes = multiplySafe(targetRxBytes, entry.rxBytes, rawRxBytes);
entry.txBytes = multiplySafe(targetTxBytes, entry.txBytes, rawTxBytes);
// We purposefully clear out packet counters to indicate
// that this data has been augmented.
entry.rxPackets = 0;