RE: CAS prevents call to ConvertTo used by custom TypeConverter
- From: stcheng@xxxxxxxxxxxxxxxxxxxx (Steven Cheng[MSFT])
- Date: Tue, 25 Oct 2005 08:42:27 GMT
Thanks for your response Jim,
If the runtime code also reference the InstanceDescriptor, I'm afraid we're
limited to granting our assembly FullTrust permission(if can not avoid
involving calling such classes). In fact, such component really need this
trust level since it can do powerful operations (creating object instance
dynamically) and it is mostly used in many fundamental classes such as the
serizalier.... I think you may consider strong-named your webcontrol
library and inform the user/admin to grant the sufficient permission (we
can apply such attribute so as to let the end user use permview tool to
check the required permissions) , just as the .NET's buildin assemblies
do(grant fulltrust through strong-name...)
Thanks,
Steven Cheng
Microsoft Online Support
Get Secure! www.microsoft.com/security
(This posting is provided "AS IS", with no warranties, and confers no
rights.)
--------------------
| Thread-Topic: CAS prevents call to ConvertTo used by custom TypeConverter
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| Subject: RE: CAS prevents call to ConvertTo used by custom TypeConverter
| Date: Mon, 24 Oct 2005 10:51:05 -0700
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| Hi Steven, thanks for your detailed reply, however it doesn't really
resolve
| the issue;
|
| 1. Good idea, and this is something I was trying, however, I've found
that
| the InstanceDescriptor code path is called even at runtime. In other
words
|
| In the .ConvertTo method, this block:
|
| } else if (targetType == typeof(InstanceDescriptor)) {
|
| InstanceDescriptor desc = null;
| ConstructorInfo ci = typeof(MyControlsCollection).GetConstructor(new
| Type[]{typeof(string)});
|
| MyControlsCollection t = (MyControlsCollection) value;
|
| --------------->>>//fails because of this call
| if (ci!=null) desc = CreateInstanceDescriptor(ci, t);
|
| return desc;
| }
|
| is being called, so separating the designer code from the runtime
assembly
| won't help. I'm not sure why the instance descriptor is being required
(if
| this isnt normal) at runtime? For the record I also changed the
CanConvertTo
| method to return false for InstanceDescriptor at runtime, I got an
exception
| saying that the convertor couldnt convert to InstanceDescriptor...
|
| 2. This is a commercial control, so we cannot always demand full trust.
|
| Any ideas;
| Is InstanceDescriptor usually a convert to target at runtime? - if not
| perhaps I've err'ed elsewhere?
|
| Thanks for your help.
| Jim
|
|
| "Steven Cheng[MSFT]" wrote:
|
| > Hi Jim,
| >
| > Welcome to ASPNET newsgroup.
| > As for the problem on calling
| > System.ComponentModel.Design.Serialization.InstanceDescriptor in custom
| > webcontrol code, it's caused by the .NET CAS model. Since the
| > System.ComponentModel.Design.Serialization.InstanceDescriptor class is
| > defined as requiring the direct caller to be grant "FullTrust"
permission,
| > we must make sure that any assembly use this class has been configured
as
| > FullTrust. So for our custom asp.net web control, the custom
control's
| > assembly is the direct caller of the
| > System.ComponentModel.Design.Serialization.InstanceDescriptor class,
and
| > since the webcontrol assembly will be loaded into ASP.NET application's
| > appdomain, so the security trust level of our custom assembly will be
| > determined by two things:
| >
| > 1. If we can explicitly configure our custom control's assembly as
| > "FullTrust" in CAS(by strong-name...), that'll be ok. Or alternatively
we
| > can also separate the code into another assembly which will be
configured
| > as "FullTrust" and [assembly:AllowPartiallyTrustedCallers]
| > e.g.
| >
| > //non fulltrust
| > MyControl.dll
| >
| > //using the InstanceDescriptor class and must have
| > [assembly:AllowPartiallyTrustedCallers] and be configured as
"FullTrust"
| > in CAS
| > MyControl.Design.dll
| >
| > attribute, then our main control assembly reference this assembly.
Thus,
| > the webcontrol can call the converter event being loaded in a
non-fulltrust
| > asp.net appdomain.
| >
| > 2. If we don't grant our custom control assembly "FullTrust", we need
to
| > make sure the web application which load our custom control assembly be
| > running under "Full" trust level, this is configured in machine.config
or
| > web.config's system.web/trust/@Level attribute, e.g:
| >
| > <trust level="Full" originUrl=""/>
| >
| > by default, asp.net application's trustLevel is configured as "Full",
| > however, some public web host may have certain constrains on this.
| >
| > If you have anything unclear, please feel free to post here.
| >
| > Thanks,
| >
| > Steven Cheng
| > Microsoft Online Support
| >
| > Get Secure! www.microsoft.com/security
| > (This posting is provided "AS IS", with no warranties, and confers no
| > rights.)
| >
| >
| >
| >
| >
| >
| >
| >
| > --------------------
| > | Thread-Topic: CAS prevents call to ConvertTo used by custom
TypeConverter
| > | thread-index: AcXWjJpZEaRQkx7oTzmBQ22uluJxdg==
| > | X-WBNR-Posting-Host: 70.68.236.247
| > | From: =?Utf-8?B?Smlt?= <jim2000@xxxxxxxxxxxxx>
| > | Subject: CAS prevents call to ConvertTo used by custom TypeConverter
| > | Date: Fri, 21 Oct 2005 15:13:02 -0700
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| > microsoft.public.dotnet.framework.aspnet.buildingcontrols:4369
| > | X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet.buildingcontrols
| > |
| > | Hi, I have a web control, that has a property (a collection of
strings)
| > with
| > | it's own editor and typeconverter.
| > |
| > | The problem is that the type converter has to ConvertTo an
| > | InstanceDescriptor at runtime, but calls InstanceDescriptor (seem to)
| > require
| > | Unrestricted permission;
| > |
| > |
| > | (permview /decl System.dll yields
| > |
| > | Class System.ComponentModel.Design.Serialization.InstanceDescriptor
| > | LinktimeDemand permission set:
| > | <PermissionSet class="System.Security.PermissionSet"
| > | version="1"
| > | Unrestricted="true"/>
| > | )
| > |
| > |
| > |
| > |
| > | Also this page
| >
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetsec/ht
| > ml/aptcatypes.asp says;
| > |
| > | The following is a list of types within these APTCA decorated
assemblies
| > | that are not callable by partially trusted code because they are
| > decorated
| > | with one of the following declarative security attributes:
| > |
| > | [PermissionSet(SecurityAction.LinkDemand, Name="FullTrust")]
| > | ...for...
| > | System.ComponentModel.Design.Serialization.InstanceDescriptor
| > |
| > |
| > |
| > |
| > | I'm perplexed - CAS sounds like a nice idea but are you seriously
telling
| > me
| > | that no-one but FullTrust users can use my code because I have a
custom
| > type
| > | converter!
| > |
| > | Is there anyway around this?
| > |
| > | Thanks in advance
| > | Jim
| > |
| > |
| > |
| > |
| > | Here's my type converter
| > |
| > | class MyControlsCollectionConverter : TypeConverter
| > | {
| > |
| > | public override bool CanConvertFrom(ITypeDescriptorContext context,
Type
| > | sourceType){
| > | if (sourceType == typeof(string)) return true;
| > | return false;
| > | }
| > |
| > |
| > | public override object ConvertFrom(ITypeDescriptorContext context,
| > | CultureInfo culture, object value) {
| > | if (value == null)
| > | return String.Empty;
| > | try{
| > | if (value.GetType() == typeof(string)){
| > | string[] IDs = ((string)value).Split(new char[]{','});
| > | MyControlsCollection r = new MyControlsCollection();
| > | for(int i=0; i<IDs.Length; i++)
| > | r.Add(IDs[i]);
| > | return r;
| > | }
| > | return null;
| > | } catch (Exception f){
| > | throw GetConvertFromException(value+f.Message);
| > | }
| > | }
| > |
| > | public override bool CanConvertTo(ITypeDescriptorContext context,
Type
| > | targetType){
| > | if (targetType == typeof(string) || targetType ==
| > | typeof(InstanceDescriptor)) return true;
| > | else return base.CanConvertTo(context, targetType);
| > | }
| > |
| > | ///<summary>Convert collection to string</summary>
| > | public override object ConvertTo(ITypeDescriptorContext context,
| > | CultureInfo culture, object value, Type targetType) {
| > |
| > |
| > | if(targetType == typeof(string)){
| > |
| > | string result = "";
| > |
| > | MyControlsCollection list = null;
| > | MyMainControl myMainControl = null;
| > | try{
| > | if(value!=null){
| > | list = (MyControlsCollection) value;
| > | if (context != null && context.Instance != null)
| > | myMainControl = ((MyMainControl)context.Instance);
| > | for(int i=0; i<list.Count; i++){
| > | result += list[i];
| > | if(i<list.Count-1) result+=",";
| > | }
| > |
| > | }
| > | } catch (Exception e){
| > | result="Internal error occured "+e.Message;
| > | throw new Exception("Error occured;"+e.Message);
| > | }
| > |
| > | return result;
| > | } else if (targetType == typeof(InstanceDescriptor)) {
| > | //sometimes it wants to convert collection to instance descriptor,
so
| > | create an instance descriptor
| > | //using string constructor
| > | InstanceDescriptor desc = null;
| > | ConstructorInfo ci =
typeof(MyControlsCollection).GetConstructor(new
| > | Type[]{typeof(string)});
| > |
| > | MyControlsCollection t = (MyControlsCollection) value;
| > |
| > | --------------->>>//fails because of this call
| > | if (ci!=null) desc = CreateInstanceDescriptor(ci, t);
| > |
| > | return desc;
| > | } else return base.ConvertTo(context,culture,value,targetType);
| > |
| > | }
| > |
| > | InstanceDescriptor CreateInstanceDescriptor(ConstructorInfo ci,
| > | MyControlsCollection t)
| > | {
| > | return new InstanceDescriptor(ci,new object[]{t.ToString()});
| > | }
| > |
| > |
| > | public override bool
GetStandardValuesExclusive(ITypeDescriptorContext
| > | context)
| > | {return false;}
| > |
| > | public override bool
GetStandardValuesSupported(ITypeDescriptorContext
| > | context)
| > | {return false;}
| > | }
| > |
| >
| >
|
.
- References:
- CAS prevents call to ConvertTo used by custom TypeConverter
- From: Jim
- RE: CAS prevents call to ConvertTo used by custom TypeConverter
- From: Steven Cheng[MSFT]
- RE: CAS prevents call to ConvertTo used by custom TypeConverter
- From: Jim
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