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Merge pull request #1345 from denislevin/denisl/cs/MishandlingJapaneseDatesAndLeapYear
C#: Japanese Era and Leap Year checks (Likely Bugs)
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‎csharp/ql/src/Likely Bugs/LeapYear/UnsafeYearConstruction.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>When creating a <code>System.DateTime</code> object by setting the year, month, and day in the constructor by performing an arithmetic operation on a different <code>DateTime</code> object, there is a risk that the date you are setting is invalid.</p>
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<p>On a leap year, such code may throw an <code>ArgumentOutOfRangeException</code> with a message of <code>"Year, Month, and Day parameters describe an unrepresentable DateTime."</code></p>
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</overview>
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<recommendation>
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<p>Creating a <code>System.DateTime</code> object based on a different <code>System.DateTime</code> object, use the appropriate methods to manipulate the date instead of arithmetic.</p>
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</recommendation>
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<example>
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<p>In this example, we are incrementing/decrementing the current date by one year when creating a new <code>System.DateTime</code> object. This may work most of the time, but on any given February 29th, the resulting value will be invalid.</p>
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<sample src="UnsafeYearConstructionBad.cs" />
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<p>To fix this bug, we add/substract years to the current date by calling <code>AddYears</code> method on it.</p>
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<sample src="UnsafeYearConstructionGood.cs" />
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</example>
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<references>
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<li>
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<a href="https://docs.microsoft.com/en-us/dotnet/api/system.datetime?view=netframework-4.8">System.DateTime Struct</a>.
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</li>
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</references>
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</qhelp>

‎csharp/ql/src/Likely Bugs/LeapYear/UnsafeYearConstruction.ql‎

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/**
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* @name Unsafe year argument for 'DateTime' constructor
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* @description Constructing a 'DateTime' struct by setting the year argument to an increment or decrement of the year of a different 'DateTime' struct
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* @kind path-problem
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* @problem.severity error
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* @id cs/unsafe-year-construction
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* @precision high
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* @tags security
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* date-time
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* reliability
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*/
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import csharp
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import DataFlow::PathGraph
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import semmle.code.csharp.dataflow.TaintTracking
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class UnsafeYearCreationFromArithmeticConfiguration extends TaintTracking::Configuration {
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UnsafeYearCreationFromArithmeticConfiguration() {
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this = "UnsafeYearCreationFromArithmeticConfiguration"
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}
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override predicate isSource(DataFlow::Node source) {
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exists(ArithmeticOperation ao, PropertyAccess pa | ao = source.asExpr() |
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pa = ao.getAChild*() and
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pa.getProperty().getQualifiedName().matches("System.DateTime.Year")
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)
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}
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override predicate isSink(DataFlow::Node sink) {
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exists(ObjectCreation oc |
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sink.asExpr() = oc.getArgumentForName("year") and
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oc.getObjectType().getABaseType*().hasQualifiedName("System.DateTime")
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)
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}
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}
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from UnsafeYearCreationFromArithmeticConfiguration config, DataFlow::PathNode source, DataFlow::PathNode sink
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where config.hasFlowPath(source, sink)
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select sink, source, sink, "This $@ based on a 'System.DateTime.Year' property is used in a construction of a new 'System.DateTime' object, flowing to the 'year' argument.", source, "arithmetic operation"

‎csharp/ql/src/Likely Bugs/LeapYear/UnsafeYearConstructionBad.cs‎

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using System;
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public class UnsafeYearConstructionBad
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{
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public UnsafeYearConstructionBad()
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{
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DateTime Start;
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DateTime End;
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var now = DateTime.UtcNow;
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// the base-date +/- n years may not be a valid date.
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Start = new DateTime(now.Year - 1, now.Month, now.Day, 0, 0, 0, DateTimeKind.Utc);
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End = new DateTime(now.Year + 1, now.Month, now.Day, 0, 0, 1, DateTimeKind.Utc);
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}
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}

‎csharp/ql/src/Likely Bugs/LeapYear/UnsafeYearConstructionGood.cs‎

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using System;
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public class UnsafeYearConstructionGood
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{
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public UnsafeYearConstructionGood()
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{
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DateTime Start;
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DateTime End;
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var now = DateTime.UtcNow;
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Start = now.AddYears(-1).Date;
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End = now.AddYears(-1).Date.AddSeconds(1);
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}
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}

‎csharp/ql/src/Likely Bugs/MishandlingJapaneseEra.cs‎

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using System;
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using System.Globalization;
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public class Example
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{
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public static void Main()
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{
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var cal = new JapaneseCalendar();
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// constructing date using current era
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var dat = cal.ToDateTime(2, 1, 2, 0, 0, 0, 0);
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Console.WriteLine($"{dat:s}");
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// constructing date using current era
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dat = new DateTime(2, 1, 2, cal);
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Console.WriteLine($"{dat:s}");
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}
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}
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// Output with the Heisei era current:
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// 1990-01-02T00:00:00
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// 1990-01-02T00:00:00
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// Output with the new era current:
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// 2020-01-02T00:00:00
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// 2020-01-02T00:00:00

‎csharp/ql/src/Likely Bugs/MishandlingJapaneseEra.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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When eras change, calling a date and time instantiation method that relies on the default era can produce an ambiguous date.
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In the example below, the call to the <code>JapaneseCalendar.ToDateTime</code> method that uses the default era returns different dates depending on whether or not the new era has been defined in the registry.
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</p>
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</overview>
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<recommendation>
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<p>Use speific era when creating DateTime and DateTimeOffset structs from previously stored date in Japanese calendar</p>
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<p>Don't store dates in Japanese format</p>
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<p>Don't use hard-coded era start date for date calculations converting dates from Japanese date format</p>
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<p>Use <code>JapaneseCalendar</code> class for date formatting only</p>
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</recommendation>
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<example>
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<p>This example demonstrates the dangers of using current year assumptions in Japanese date conversions</p>
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<sample src="MishandlingJapaneseEra.cs" />
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</example>
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<references>
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<li>
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<a href="https://devblogs.microsoft.com/dotnet/handling-a-new-era-in-the-japanese-calendar-in-net/">Handling a new era in the Japanese calendar in .NET</a>.
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</li>
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<li>
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<a href="https://blogs.msdn.microsoft.com/shawnste/2018/04/12/the-japanese-calendars-y2k-moment/">The Japanese Calendar's Y2K Moment</a>.
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</li>
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<li>
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<a href="https://docs.microsoft.com/en-us/windows/desktop/Intl/era-handling-for-the-japanese-calendar/">Era Handling for the Japanese Calendar</a>.
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</li>
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<li>
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<a href="https://simple.wikipedia.org/wiki/List_of_Japanese_eras">List of Japanese Eras (Wikipedia)</a>
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</li>
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</references>
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</qhelp>

‎csharp/ql/src/Likely Bugs/MishandlingJapaneseEra.ql‎

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/**
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* @name Mishandling the Japanese era start date
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* @description Japanese era should be handled with the built-in 'JapaneseCalendar' class. Avoid hard-coding Japanese era start dates and names.
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* @id cs/mishandling-japanese-era
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* @kind problem
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* @problem.severity warning
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* @precision medium
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* @tags reliability
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* date-time
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*/
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import csharp
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/**
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* Holds if `year`, `month`, and `day` specify the start of a new era
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* (see https://simple.wikipedia.org/wiki/List_of_Japanese_eras).
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*/
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predicate isEraStart(int year, int month, int day) {
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year = 1989 and month = 1 and day = 8
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or
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year = 2019 and month = 5 and day = 1
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}
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predicate isExactEraStartDateCreation(ObjectCreation cr) {
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(
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cr.getType().hasQualifiedName("System.DateTime") or
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cr.getType().hasQualifiedName("System.DateTimeOffset")
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) and
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isEraStart(cr.getArgument(0).getValue().toInt(), cr.getArgument(1).getValue().toInt(), cr.getArgument(2).getValue().toInt())
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}
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predicate isDateFromJapaneseCalendarToDateTime(MethodCall mc) {
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(
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mc.getQualifier().getType().hasQualifiedName("System.Globalization.JapaneseCalendar") or
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mc.getQualifier().getType().hasQualifiedName("System.Globalization.JapaneseLunisolarCalendar")
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) and
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mc.getTarget().hasName("ToDateTime") and
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mc.getArgument(0).hasValue() and
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(
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mc.getNumberOfArguments() = 7 // implicitly current era
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or
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mc.getNumberOfArguments() = 8 and
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mc.getArgument(7).getValue() = "0"
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) // explicitly current era
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}
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predicate isDateFromJapaneseCalendarCreation(ObjectCreation cr) {
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(
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cr.getType().hasQualifiedName("System.DateTime") or
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cr.getType().hasQualifiedName("System.DateTimeOffset")
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) and
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(
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cr
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.getArgumentForName("calendar")
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.getType()
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.hasQualifiedName("System.Globalization.JapaneseCalendar") or
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cr
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.getArgumentForName("calendar")
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.getType()
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.hasQualifiedName("System.Globalization.JapaneseLunisolarCalendar")
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) and
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cr.getArgumentForName("year").hasValue()
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}
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from Expr expr, string message
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where
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isDateFromJapaneseCalendarToDateTime(expr) and message = "'DateTime' created from Japanese calendar with explicit or current era and hard-coded year."
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or
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isDateFromJapaneseCalendarCreation(expr) and message = "'DateTime' constructed from Japanese calendar with explicit or current era and hard-coded year."
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or
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isExactEraStartDateCreation(expr) and message = "Hard-coded the beginning of the Japanese Heisei era."
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select expr, message

‎csharp/ql/test/query-tests/Likely Bugs/MishandlingJapaneseEra/MishandlingJapaneseEra.expected‎

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| Program.cs:12:31:12:54 | object creation of type DateTime | Hard-coded the beginning of the Japanese Heisei era. |
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| Program.cs:15:66:15:89 | object creation of type DateTime | Hard-coded the beginning of the Japanese Heisei era. |
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| Program.cs:22:42:22:98 | object creation of type DateTimeOffset | Hard-coded the beginning of the Japanese Heisei era. |
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| Program.cs:29:37:29:71 | call to method ToDateTime | 'DateTime' created from Japanese calendar with explicit or current era and hard-coded year. |
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| Program.cs:33:27:33:64 | call to method ToDateTime | 'DateTime' created from Japanese calendar with explicit or current era and hard-coded year. |
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| Program.cs:49:28:49:73 | object creation of type DateTime | 'DateTime' constructed from Japanese calendar with explicit or current era and hard-coded year. |

‎csharp/ql/test/query-tests/Likely Bugs/MishandlingJapaneseEra/MishandlingJapaneseEra.qlref‎

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Likely Bugs/MishandlingJapaneseEra.ql

‎csharp/ql/test/query-tests/Likely Bugs/MishandlingJapaneseEra/Program.cs‎

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using System;
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using System.Collections.Generic;
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using System.Globalization;
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namespace JapaneseDates
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{
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class Program
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{
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static void Main(string[] args)
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{
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// BAD: hard-coded era start date
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var henseiStart = new DateTime(1989, 1, 8);
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// BAD: hard-coded era start dates, list
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List<DateTime> listOfEraStart = new List<DateTime> { new DateTime(1989, 1, 8) };
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// BAD: hardcoded era name
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string currentEra = "Heisei";
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DateTimeOffset dateNow = DateTimeOffset.Now;
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DateTimeOffset dateThisEra = new DateTimeOffset(1989, 1, 8, 0, 0, 0, 0, TimeSpan.Zero);
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CultureInfo japaneseCulture = CultureInfo.GetCultureInfo("ja-JP");
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JapaneseCalendar jk = new JapaneseCalendar();
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// BAD: datetime is created from constant year in the current era, and the result will change with era change
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var datejkCurrentEra = jk.ToDateTime(32, 2, 1, 9, 9, 9, 9);
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Console.WriteLine("Date for datejkCurrentEra {0} and year {1}", datejkCurrentEra.ToString(japaneseCulture), jk.GetYear (datejkCurrentEra));
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// BAD: datetime is created from constant year in the current era, and the result will change with era change
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var datejk = jk.ToDateTime(32, 2, 1, 9, 9, 9, 9, 0);
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Console.WriteLine("Date for jk {0} and year {1}", datejk.ToString(japaneseCulture), jk.GetYear (datejk));
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// OK: datetime is created from constant year in the specific era, and the result will not change with era change
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var datejk1 = jk.ToDateTime(32, 2, 1, 9, 9, 9, 9, 4);
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Console.WriteLine("Date for jk {0} and year {1}", datejk1.ToString(japaneseCulture), jk.GetYear (datejk1));
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// OK: year is not hard-coded, i.e. it may be updated
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var datejk0 = jk.ToDateTime(jk.GetYear(datejk), 2, 1, 9, 9, 9, 9);
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Console.WriteLine("Date for jk0 {0} and year {1}", datejk0, jk.GetYear(datejk0));
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// BAD: hard-coded year conversion
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int realYear = 1988 + jk.GetYear(datejk);
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Console.WriteLine("Which converts to year {0}", realYear);
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// BAD: creating DateTime using specified Japanese era date. This may yield a different date when era changes
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DateTime val = new DateTime(32, 2, 1, new JapaneseCalendar());
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Console.WriteLine("DateTime from constructor {0}", val);
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// OK: variable data for Year, not necessarily hard-coded and can come from adjusted source
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DateTime val1 = new DateTime(jk.GetYear(datejk), 2, 1, new JapaneseCalendar());
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Console.WriteLine("DateTime from constructor {0}", val);
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}
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}
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}

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