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//
// Gendarme.Rules.Concurrency.ProtectCallsToEventDelegatesRule
//
// Authors:
// Sebastien Pouliot <sebastien@ximian.com>
//
// Copyright (C) 2008 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Globalization;
using Mono.Cecil;
using Mono.Cecil.Cil;
using Gendarme.Framework;
using Gendarme.Framework.Engines;
using Gendarme.Framework.Helpers;
using Gendarme.Framework.Rocks;
namespace Gendarme.Rules.Concurrency {
/// <summary>
/// This rule checks that event invocations are safely implemented. In particular,
/// the event must be copied into a local to avoid race conditions and it must be
/// checked for null before it is used (events will normally be null until a delegate is added
/// to them).
/// </summary>
/// <example>
/// Bad example (no check):
/// <code>
/// public event EventHandler Loading;
///
/// protected void OnLoading (EventArgs e)
/// {
/// // Loading field could be null, throwing a NullReferenceException
/// Loading (this, e);
/// }
/// </code>
/// </example>
/// <example>
/// Bad example (race condition):
/// <code>
/// public event EventHandler Loading;
///
/// protected void OnLoading (EventArgs e)
/// {
/// // Loading could be non-null here
/// if (Loading != null) {
/// // but be null once we get here :(
/// Loading (this, e);
/// }
/// }
/// </code>
/// </example>
/// <example>
/// Good example:
/// <code>
/// public event EventHandler Loading;
/// protected void OnLoading (EventArgs e)
/// {
/// EventHandler handler = Loading;
/// // handler is either null or non-null
/// if (handler != null) {
/// // and won't change (i.e. safe from a NullReferenceException)
/// handler (this, e);
/// // however it is still possible, like the original code, that
/// // the Loading method will be removed before, or during its
/// // execution. Your code should be safe against such occurance.
/// }
/// }
/// </code>
/// </example>
[Problem ("The use of the event does not seems protected properly against NullReferenceException and/or race conditions.")]
[Solution ("Fix the event use to make sure it won't be null or susceptible to a race condition.")]
[EngineDependency (typeof (OpCodeEngine))]
public class ProtectCallToEventDelegatesRule : Rule, IMethodRule {
static private bool CheckNull (Instruction ins)
{
switch (ins.OpCode.Code) {
// csc does a ldloc.x + ldnull + ceq for: if (variable == null)
case Code.Ldnull:
return (ins.Next.OpCode.Code == Code.Ceq);
// [g]mcs will do a Br[true|false][.s]
case Code.Brfalse:
case Code.Brfalse_S:
case Code.Brtrue:
case Code.Brtrue_S:
return true;
case Code.Ceq:
// csc does a ldnull + ldloc.x + ceq for: if (null == variable)
return (ins.Previous.Previous.OpCode.Code == Code.Ldnull);
default:
return false;
}
}
static private bool CheckVariable (MethodDefinition method, Instruction ins, VariableReference load)
{
// walkback to find the previous use of the variable
Instruction previous = ins.Previous;
while (previous != null) {
VariableDefinition variable = previous.GetVariable (method);
// are we talking about the same variable ?
if ((variable != null) && (load.Index == variable.Index)) {
if (previous.IsStoreLocal ()) {
return false;
} else {
// load, check for null check
if (CheckNull (previous.Next))
return true;
}
}
previous = previous.Previous;
}
return true;
}
public RuleResult CheckMethod (MethodDefinition method)
{
// rule does not apply to method without IL (e.g. p/invoke) or generated code (e.g. compiler or tools)
if (!method.HasBody || method.IsGeneratedCode ())
return RuleResult.DoesNotApply;
// avoid looping if we're sure there's no call in the method
if (!OpCodeBitmask.Calls.Intersect (OpCodeEngine.GetBitmask (method)))
return RuleResult.DoesNotApply;
foreach (Instruction ins in method.Body.Instructions) {
if ((ins.OpCode.Code != Code.Callvirt) && (ins.OpCode.Code != Code.Call))
continue;
// look for calls to .Invoke
MethodReference mr = (ins.Operand as MethodReference);
if (!MethodSignatures.Invoke.Matches (mr))
continue;
// limit ourself to events
if (!mr.IsEventCallback ())
continue;
// first check if we're looking from a variable or directly from
// the field (bad, it could be null)
Instruction caller = ins.TraceBack (method);
FieldDefinition field = caller.GetField ();
if (field != null) {
string msg = String.Format (CultureInfo.InvariantCulture, "Possible race condition since field '{0}' is accessed directly.", field.Name);
Runner.Report (method, ins, Severity.High, Confidence.High, msg);
} else {
// look for the variable, if it's not then stop analysis
VariableDefinition load = caller.GetVariable (method);
if ((load != null) && !CheckVariable (method, caller, load)) {
string msg = String.Format (CultureInfo.InvariantCulture, "Variable '{0}' does not seems to be checked against null.", load.Name);
Runner.Report (method, ins, Severity.High, Confidence.Normal, msg);
}
}
}
return Runner.CurrentRuleResult;
}
}
}
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