[Mono-bugs] [Bug 668506] New: Type.IsAssignableFrom can segfault with contravariant delegates

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https://bugzilla.novell.com/show_bug.cgi?id=668506

https://bugzilla.novell.com/show_bug.cgi?id=668506#c0


           Summary: Type.IsAssignableFrom can segfault with contravariant
                    delegates
    Classification: Mono
           Product: Mono: Runtime
           Version: SVN
          Platform: x86-64
        OS/Version: Linux
            Status: NEW
          Severity: Major
          Priority: P5 - None
         Component: generics
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: knielsen at ariasolutions.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: Community User
           Blocker: ---


Description of Problem:

The mono runtime will segfault when calling Type.IsAssignableFrom with "this"
equal to a constructed contravariant generic delegate, and with "c" equal
to the generic type definition of the same delegate.

Steps to reproduce the problem:

1. run the following program:

using System;
using System.Reflection;

namespace MonoGenericsCrash
{
  static class IsAssignableFromTest
  {
    delegate void MyAction<in T>(T ag);

    public static void Main()
    {
      typeof(MyAction<string>).IsAssignableFrom(typeof(MyAction<>));
    }
  }
}

Actual Results: Program segfaults:

#6  mono_class_is_variant_compatible (klass="MyAction`1", oklass="MyAction`1")
at class.c:7206
#7  0x0000000000509633 in mono_class_is_assignable_from (klass="MyAction`1",
oklass="MyAction`1") at class.c:7293
#8  0x0000000041182410 in ?? ()
#9  0x00000000024c7780 in ?? ()
#10 0x00007f881a1b1d48 in ?? ()
#11 0x0000000000000000 in ?? ()

Expected Results: Program should not segfault
How often does this happen? always

Additional Information:

The problem appears to be in the mono_class_is_assignable_from method. Before
calling mono_class_is_variant_compatible with the two delegate types, it should
probably check to make sure both types have variant generic params, instead of
just the first type.

I will attach a patch that fixes this issue.

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