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Fix overflow traps in DispatchTime/DispatchWallTime/DispatchTimeInterval #11927

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Merged
merged 1 commit into from
Sep 20, 2017
Merged

Fix overflow traps in DispatchTime/DispatchWallTime/DispatchTimeInterval #11927

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57 changes: 42 additions & 15 deletions stdlib/public/SDK/Dispatch/Time.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,41 @@ extension DispatchWallTime {
}
}


// Returns m1 * m2, clamped to the range [Int64.min, Int64.max].
// Because of the way this function is used, we can always assume
// that m2 > 0.
private func clampedInt64Product(_ m1: Int64, _ m2: Int64) -> Int64 {
assert(m2 > 0, "multiplier must be positive")
let (result, overflow) = m1.multipliedReportingOverflow(by: m2)
if overflow {
return m1 > 0 ? Int64.max : Int64.min
}
return result
}

// Returns its argument clamped to the range [Int64.min, Int64.max].
private func toInt64Clamped(_ value: Double) -> Int64 {
if value.isNaN { return Int64.max }
if value >= Double(Int64.max) { return Int64.max }
if value <= Double(Int64.min) { return Int64.min }
return Int64(value)
}

/// Represents a time interval that can be used as an offset from a `DispatchTime`
/// or `DispatchWallTime`.
///
/// For example:
/// let inOneSecond = DispatchTime.now() + DispatchTimeInterval.seconds(1)
///
/// If the requested time interval is larger then the internal representation
/// permits, the result of adding it to a `DispatchTime` or `DispatchWallTime`
/// is `DispatchTime.distantFuture` and `DispatchWallTime.distantFuture`
/// respectively. Such time intervals compare as equal:
///
/// let t1 = DispatchTimeInterval.seconds(Int.max)
/// let t2 = DispatchTimeInterval.milliseconds(Int.max)
/// let result = t1 == t2 // true
public enum DispatchTimeInterval : Equatable {
case seconds(Int)
case milliseconds(Int)
Expand All @@ -124,9 +159,9 @@ public enum DispatchTimeInterval : Equatable {

internal var rawValue: Int64 {
switch self {
case .seconds(let s): return Int64(s) * Int64(NSEC_PER_SEC)
case .milliseconds(let ms): return Int64(ms) * Int64(NSEC_PER_MSEC)
case .microseconds(let us): return Int64(us) * Int64(NSEC_PER_USEC)
case .seconds(let s): return clampedInt64Product(Int64(s), Int64(NSEC_PER_SEC))
case .milliseconds(let ms): return clampedInt64Product(Int64(ms), Int64(NSEC_PER_MSEC))
case .microseconds(let us): return clampedInt64Product(Int64(us), Int64(NSEC_PER_USEC))
case .nanoseconds(let ns): return Int64(ns)
case .never: return Int64.max
}
Expand All @@ -153,16 +188,12 @@ public func -(time: DispatchTime, interval: DispatchTimeInterval) -> DispatchTim
}

public func +(time: DispatchTime, seconds: Double) -> DispatchTime {
let interval = seconds * Double(NSEC_PER_SEC)
let t = __dispatch_time(time.rawValue,
interval.isInfinite || interval.isNaN ? Int64.max : Int64(interval))
let t = __dispatch_time(time.rawValue, toInt64Clamped(seconds * Double(NSEC_PER_SEC)));
return DispatchTime(rawValue: t)
}

public func -(time: DispatchTime, seconds: Double) -> DispatchTime {
let interval = -seconds * Double(NSEC_PER_SEC)
let t = __dispatch_time(time.rawValue,
interval.isInfinite || interval.isNaN ? Int64.min : Int64(interval))
let t = __dispatch_time(time.rawValue, toInt64Clamped(-seconds * Double(NSEC_PER_SEC)));
return DispatchTime(rawValue: t)
}

Expand All @@ -177,15 +208,11 @@ public func -(time: DispatchWallTime, interval: DispatchTimeInterval) -> Dispatc
}

public func +(time: DispatchWallTime, seconds: Double) -> DispatchWallTime {
let interval = seconds * Double(NSEC_PER_SEC)
let t = __dispatch_time(time.rawValue,
interval.isInfinite || interval.isNaN ? Int64.max : Int64(interval))
let t = __dispatch_time(time.rawValue, toInt64Clamped(seconds * Double(NSEC_PER_SEC)));
return DispatchWallTime(rawValue: t)
}

public func -(time: DispatchWallTime, seconds: Double) -> DispatchWallTime {
let interval = -seconds * Double(NSEC_PER_SEC)
let t = __dispatch_time(time.rawValue,
interval.isInfinite || interval.isNaN ? Int64.min : Int64(interval))
let t = __dispatch_time(time.rawValue, toInt64Clamped(-seconds * Double(NSEC_PER_SEC)));
return DispatchWallTime(rawValue: t)
}
59 changes: 57 additions & 2 deletions test/stdlib/Dispatch.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -126,21 +126,47 @@ DispatchAPI.test("DispatchTime.addSubtract") {
expectEqual(DispatchTime(uptimeNanoseconds: 1), then)

then = DispatchTime.now() - Double.nan
expectEqual(DispatchTime.distantFuture, then)

then = DispatchTime.now() + Date.distantFuture.timeIntervalSinceNow
expectEqual(DispatchTime(uptimeNanoseconds: UInt64.max), then)

then = DispatchTime.now() + Date.distantPast.timeIntervalSinceNow
expectEqual(DispatchTime(uptimeNanoseconds: 1), then)

then = DispatchTime.now() - Date.distantFuture.timeIntervalSinceNow
expectEqual(DispatchTime(uptimeNanoseconds: 1), then)

then = DispatchTime.now() - Date.distantPast.timeIntervalSinceNow
expectEqual(DispatchTime(uptimeNanoseconds: UInt64.max), then)
}

DispatchAPI.test("DispatchWallTime.addSubtract") {
let distantPastRawValue = DispatchWallTime.distantFuture.rawValue - UInt64(1)

var then = DispatchWallTime.now() + Double.infinity
expectEqual(DispatchWallTime.distantFuture, then)

then = DispatchWallTime.now() + Double.nan
expectEqual(DispatchWallTime.distantFuture, then)

then = DispatchWallTime.now() - Double.infinity
expectEqual(DispatchWallTime.distantFuture.rawValue - UInt64(1), then.rawValue)
expectEqual(distantPastRawValue, then.rawValue)

then = DispatchWallTime.now() - Double.nan
expectEqual(DispatchWallTime.distantFuture.rawValue - UInt64(1), then.rawValue)
expectEqual(DispatchWallTime.distantFuture, then)

then = DispatchWallTime.now() + Date.distantFuture.timeIntervalSinceNow
expectEqual(DispatchWallTime.distantFuture, then)

then = DispatchWallTime.now() + Date.distantPast.timeIntervalSinceNow
expectEqual(distantPastRawValue, then.rawValue)

then = DispatchWallTime.now() - Date.distantFuture.timeIntervalSinceNow
expectEqual(distantPastRawValue, then.rawValue)

then = DispatchWallTime.now() - Date.distantPast.timeIntervalSinceNow
expectEqual(DispatchWallTime.distantFuture, then)
}

DispatchAPI.test("DispatchTime.uptimeNanos") {
Expand Down Expand Up @@ -516,6 +542,35 @@ if #available(OSX 10.13, iOS 11.0, watchOS 4.0, tvOS 11.0, *) {
}
}

DispatchAPI.test("DispatchTimeInterval") {
// Basic tests that the correct value is stored and the == method works
for i in stride(from:1, through: 100, by: 5) {
expectEqual(DispatchTimeInterval.seconds(i), DispatchTimeInterval.milliseconds(i * 1000))
expectEqual(DispatchTimeInterval.milliseconds(i), DispatchTimeInterval.microseconds(i * 1000))
expectEqual(DispatchTimeInterval.microseconds(i), DispatchTimeInterval.nanoseconds(i * 1000))
}


// Check some cases that used to cause arithmetic overflow when evaluating the rawValue for ==
var t = DispatchTimeInterval.seconds(Int.max)
expectTrue(t == t) // This would crash.

t = DispatchTimeInterval.seconds(-Int.max)
expectTrue(t == t) // This would crash.

t = DispatchTimeInterval.milliseconds(Int.max)
expectTrue(t == t) // This would crash.

t = DispatchTimeInterval.milliseconds(-Int.max)
expectTrue(t == t) // This would crash.

t = DispatchTimeInterval.microseconds(Int.max)
expectTrue(t == t) // This would crash.

t = DispatchTimeInterval.microseconds(-Int.max)
expectTrue(t == t) // This would crash.
}

#if swift(>=4.0)
DispatchAPI.test("DispatchTimeInterval.never.equals") {
expectTrue(DispatchTimeInterval.never == DispatchTimeInterval.never)
Expand Down