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Article : Code Access Security Part - 2 (.Net FrameWork Tools Series)

 
 
Namratha Shah \(Nasha\)
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      11-06-2004

Hey Guys,

Before we start with our sample app we need to view the security
configuration files on the machine. You will find them under

<drive>\WInNT\Microsoft.NET\FrameWork\<version>\Co nfig

Enterprise Level Security configuration file is :- enterprise.config

Machine Level Security configuration file is :- security.config



You will find the user security configuration file in

<drive>:\Documents and Settings\<userprofile>\Application

Data\Microsoft\CLR Security Config\v1.1.4322\security.config

Let us now create our sample app.In this we will create .Windows Forms
application which will try and read and write to the local disk.

1) Go to VS.NET create a new Win App.

2) On the Form Place one text box And one button Make the multiline property
of the text box true.

3) In the click event of the button write the followinf piece of code which
writes to a file wat ever is written in the text box.

StreamWriter sWriter = new StreamWriter("C://MyTextFile.txt");

sWriter.Write(textBox1.Text);

sWriter.Flush();

sWriter.Close();

4) If you run this from your machine you will be able to create the file and
write the textbox contents in it.

Well Currently this code is executing on the local machine cause in the
local mahinc policy MyComputer Zone has Full trust permission set.

Check it out by typing caspol -m -lg


Suppose if we were to run this same app from a local network share then the
Intranet code access group does not have the permission to write to the
local hard disk.

5) Place the exe on a network share and execut it. It should give you a
Security Permission Exception.

6) Modify your code to catch the exception and give a user friendly message.
Run the file again from the network share.

Suppose that we wanted this application to run from the network share. For
that we will need to change the Intranet Permission set.

caspol.exe -chggroup 1.2 FulTrust. // This command tells to fully trust all
the intranet applications

Note : Please be extremely careful to chagne the permission sets as this can
coz a lot viruses and other spy wares to come in. Change the permission sets
only if you have not made any custom changes to your PC. After changing the
permission set use

caspol.exe -reset command this resets the .NET default permission sets for
all code groups

Thus in this way we can prevent malicious code to access our resources.

Lets now explore the other options of caspol.exe

Turning the Security On/Off

It is possible to turn the .Net Security Off if so for any reason. By

default it is On.

caspol.exe -security off // to turn of the .Net security

To reset the security to .Net default security use

caspol.exe -reset

To create a new code group

caspol.exe -addgroup 1.3 -site www. <name of the site> /// this will add
full trust for any content from this site.

To create a code group under intranet with fulltrust to a particular share
on the network

caspol.exe -addgroup 1.2 -url file:///\\<machinename>/<foldername>/*
FullTrust

To remove a code group give the codegroup number (as shown in the list
groups) with -remgroup option

caspol.exe -remgroup 1.3.2

To change the code group's permission( we just sw above when we changed the
permission for our intranet code group)

caspol.exe -chggroup 1.2 FullTrust

You can add code group for a particular strong name E.g. If you have an
application MyApp.exe and you want any version of this application have
FullTrust you can achieve that by using the a similar command

caspol.exe -addgroup l -strong -file \bin\debug\MyApp.exe -
noname -noversion FullTrust

This command will a new strong Name code group. You can view it by giving
caspol -lg command.

You will see that are already 2 strong name code groups installed by
default. They belong to Microsoft and ECMA.



-- Please post your queries and comments for my articles in the usergroup
for the benefit of all. I hope this step from my end is helpful to all of
us.

Regards,

Namratha (Nasha)





 
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