making permissions optional

Discussion in 'ASP .Net Security' started by David Thielen, Nov 20, 2006.

  1. Hi;

    I have the following method:
    public static InputStream loadResource(String filename, int location)
    throws IOException

    if ((filename == null) || (filename.length() == 0))
    return null;

    if ((location & (THREAD | APP_CLASS | SYSTEM_CLASS)) != 0)
    System.IO.Stream stream =
    if (stream != null)
    return new JavaInputStream(stream);

    // file
    if ((location & FILE) != 0) {
    File file = new File(filename);
    if (file.exists()) {
    if (log.isInfoEnabled())"Loading resource file: " + new
    return new FileInputStream(file);

    // url last
    if ((location & URL) != 0) {
    try {
    URL url = new URL(filename);
    if (log.isInfoEnabled())"Loading resource file: " + new
    return url.openStream();
    } catch (MalformedURLException mue) {
    // nothing

    return null;

    And it's permissions demanded are:
    <Method Sig="class InputStream loadResource(string , int )">
    <PermissionSet version="1"
    <IPermission version="1"
    class="System.Security.Permissions.EnvironmentPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Read="UserName" />
    <IPermission version="1"
    class="System.Security.Permissions.FileIOPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Unrestricted="true" />
    <IPermission version="1"
    class="System.Security.Permissions.ReflectionPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Flags="MemberAccess" />
    <IPermission version="1"
    class="System.Security.Permissions.RegistryPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Unrestricted="true" />
    <IPermission version="1"
    class="System.Security.Permissions.SecurityPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Flags="UnmanagedCode, ControlThread, ControlEvidence" />
    <IPermission version="1"
    class="System.Security.Permissions.KeyContainerPermission, mscorlib,
    Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Unrestricted="true" />
    <PermissionSet version="1"
    class="System.Security.PermissionSet" Unrestricted="true" />

    However, all of the above permissions are not required to run our program.
    In most cases the GetManifestResourceStream is the only part used. How do I
    set this to say that these requests are optional not required?

    I hope it's not having to go set permissions on each method throughout our
    code because that would take weeks.

    thanks - dave

    Cubicle Wars -
    David Thielen, Nov 20, 2006
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  2. Hi Dave,

    The Permission Calculator Tool calculates the minimum permission set
    required to run an application by examining all applicable code paths of
    all application assemblies and dependency assemblies:

    #Permission Calculator Tool (Permcalc.exe)
    Starting from the entry point of the application, the tool traces all code
    paths through all application assemblies and the shared and system
    libraries called from the application. The tool maintains a simulated call
    stack that contains all the assemblies involved in the code path trace. On
    every code path trace, the tool checks for the presence of declarative
    demands, link demands, and declarative stack walk modifiers.

    If you use Reflector to view J# Assembly.GetManifestResourceStream(), you
    will find one of its called function has unsafe signature:

    internal virtual unsafe Stream GetManifestResourceStream(string name, ref
    StackCrawlMark stackMark, bool skipSecurityCheck)

    The resulting permission set is calculated using the all code paths. That's
    why you're seeing some permission sets that are never used in your code

    If your Web application contains code that requires more permissions than
    are granted by a particular ASP.NET trust level, the easiest option is
    customizing a policy file to grant the additional code access security
    permission to your Web application. You can either modify an existing
    policy file and grant additional permissions or create a new one based on
    an existing policy file.

    Another approach that does not require an update to ASP.NET code access
    security policy is wrapping your resource access code in its own wrapper
    assembly and configuring machine-level code access security policy to grant
    the specific assembly the appropriate permission. Then you can sandbox the
    higher-privileged code using the CodeAccessPermission.Assert method so you
    do not have to change the overall permission grant of the Web application.
    The Assert method prevents the security demand issued by the resource
    access code from propagating back up the call stack beyond the boundaries
    of the wrapper assembly.

    For more information about above two different approaches, please refer to
    following article:

    #Using Code Access Security with ASP.NET

    Walter Wang (, remove 'online.')
    Microsoft Online Community Support

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    Walter Wang [MSFT], Nov 21, 2006
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