RE: Activator.CreateInstance & LinkDemand for custom permission

From: Shawn Farkas (shawnfa_at_online.microsoft.com)
Date: 01/22/04 

Date: Thu, 22 Jan 2004 20:20:55 GMT

You are correct, the reason you're seeing that problem is that using a late-bound invocation of a method will turn any LinkDemands into full stack
walks. For your second question, there is no way for you to determine the grants of each assembly on the stack. However, I see no reason that
this should be necessary in your case. What you need to do is immediately before you use reflection to call your method, assert whatever
permissions are link demanded by that method. Then, when the method is done, immediately revoke the assertion using the RevertAssert
method of the permission set you Asserted in the first place.

Remember, asserting permissions is a dangerous activity, and you need to be very careful when doing it. Make sure that malicious code has no
way of tricking your method into doing a privileged operation for it. Revoking the assert immediately after you're done calling the method will help
to limit the time window that you are vouching for all of your callers, and limit the attack surface of this method.

-Shawn
http://blogs.msdn.com/shawnfa 

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>Thread-Topic: Activator.CreateInstance & LinkDemand for custom permission
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>Subject: RE: Activator.CreateInstance & LinkDemand for custom permission
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>Ok. I've found that Framework actually expands LinkDemant into full stack walk and therefore fails during Demand() upon some distant client 
code. In order to make it work I need to Assert appropriate permission to direct caller, so here is a question: How can I get the permission set of 
the caller from stack? Is there some way to walk through stack in order to get callers permissions?
Thanks!
>

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