SecurityPermission problem

29 Mar 2006 2:26 PM

Itay Sandbank

Hi.

I'm trying to understand how to use CAS, and found something strange. I'm
trying to deny my program of a few permissions to see what happens. I created
a small program that creates the file c:\hello.txt and exits:

[assembly: FileIOPermission(SecurityAction.RequestRefuse,
ViewAndModify="c:\\")]
namespace CodeAccessSecurity
{
    class Program
    {
        static void Main(string[] args)
        {
            FileIOPermission fip = new
FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
            fip.Demand();
            FileStream fw = new FileStream("c:\\hello.txt", FileMode.Create);
        }
    }
}

When I run it, I see a SecurityException thrown, as can be expected.
However, it is thrown when I create the FileStream and not when I Demand the
FileIOPermission.

When running from the local intranet zone (I changed the debugger's
security settings), the exception is thrown on the Demand - as I expected in
the first place.

What's going on here?

Thanks,
Itay.

30 Mar 2006 3:03 PM

Nicole Calinoiu

The Demand method skips the call stack frame for the method from which it is
called. In order to have your assembly included in the stack walk initiated
by Demand, you'll need to move it into a separate method since the Main
method has no within-assembly callers. e.g.:

static void Main(string[] args)
{
    DemandFileIOPermission();
    FileStream fw = new FileStream("c:\\hello.txt", FileMode.Create);
}

private static void DemandFileIOPermission()
{
    FileIOPermission fip = new
FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
    fip.Demand();
}

Show quoteHide quote

"Itay Sandbank" <ItaySandb***@discussions.microsoft.com> wrote in message
news:B50075F7-3042-45F6-901E-3B295B5D191A@microsoft.com...
> Hi.
>
> I'm trying to understand how to use CAS, and found something strange. I'm
> trying to deny my program of a few permissions to see what happens. I
> created
> a small program that creates the file c:\hello.txt and exits:
>
> [assembly: FileIOPermission(SecurityAction.RequestRefuse,
> ViewAndModify="c:\\")]
> namespace CodeAccessSecurity
> {
>    class Program
>    {
>        static void Main(string[] args)
>        {
>            FileIOPermission fip = new
> FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
>            fip.Demand();
>            FileStream fw = new FileStream("c:\\hello.txt",
> FileMode.Create);
>        }
>    }
> }
>
> When I run it, I see a SecurityException thrown, as can be expected.
> However, it is thrown when I create the FileStream and not when I Demand
> the
> FileIOPermission.
>
> When running from the local intranet zone (I changed the debugger's
> security settings), the exception is thrown on the Demand - as I expected
> in
> the first place.
>
> What's going on here?
>
> Thanks,
> Itay.

30 Mar 2006 4:11 PM

Itay Sandbank

I get it, thanks.

This is confusing behavior - having Demand check ALMOST everything. Is
there a reason for it or is it a bug?

Itay.

Show quoteHide quote

"Nicole Calinoiu" wrote:

> The Demand method skips the call stack frame for the method from which it is
> called. In order to have your assembly included in the stack walk initiated
> by Demand, you'll need to move it into a separate method since the Main
> method has no within-assembly callers. e.g.:
>
> static void Main(string[] args)
> {
>     DemandFileIOPermission();
>     FileStream fw = new FileStream("c:\\hello.txt", FileMode.Create);
> }
>
> private static void DemandFileIOPermission()
> {
>     FileIOPermission fip = new
> FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
>     fip.Demand();
> }
>
>
> "Itay Sandbank" <ItaySandb***@discussions.microsoft.com> wrote in message
> news:B50075F7-3042-45F6-901E-3B295B5D191A@microsoft.com...
> > Hi.
> >
> > I'm trying to understand how to use CAS, and found something strange. I'm
> > trying to deny my program of a few permissions to see what happens. I
> > created
> > a small program that creates the file c:\hello.txt and exits:
> >
> > [assembly: FileIOPermission(SecurityAction.RequestRefuse,
> > ViewAndModify="c:\\")]
> > namespace CodeAccessSecurity
> > {
> >    class Program
> >    {
> >        static void Main(string[] args)
> >        {
> >            FileIOPermission fip = new
> > FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
> >            fip.Demand();
> >            FileStream fw = new FileStream("c:\\hello.txt",
> > FileMode.Create);
> >        }
> >    }
> > }
> >
> > When I run it, I see a SecurityException thrown, as can be expected.
> > However, it is thrown when I create the FileStream and not when I Demand
> > the
> > FileIOPermission.
> >
> > When running from the local intranet zone (I changed the debugger's
> > security settings), the exception is thrown on the Demand - as I expected
> > in
> > the first place.
> >
> > What's going on here?
> >
> > Thanks,
> > Itay.
>
>

30 Mar 2006 5:29 PM

Nicole Calinoiu

This is by design (see the remarks section at
http://msdn.microsoft.com/library/en-us/cpref/html/frlrfsystemsecuritycodeaccesspermissionclassdemandtopic.asp
for details).

Demands are intended to be made by code defining resources that require
protection. Their purpose is to determine whether code attempting to use a
resource possess the necessary permission(s), not whether the code defining
the resource has those same permissions. For example, the FileStream code
that actually accesses a file on disk makes a FileIOPermission demand. It
defines the resource, so it makes the demand. Since it's calling into
unmanaged code, it gets subjected to a different demand. However, there's
no point in asking it to fulfill the FileIOPermission demand that it invokes
since it can obviously bypass that same demand simply by not making it in
the first place.

Show quoteHide quote

"Itay Sandbank" <ItaySandb***@discussions.microsoft.com> wrote in message
news:2D68C4F7-E524-46A8-B62D-4BB2FCB0C0C0@microsoft.com...
> I get it, thanks.
>
> This is confusing behavior - having Demand check ALMOST everything. Is
> there a reason for it or is it a bug?
>
> Itay.
>
> "Nicole Calinoiu" wrote:
>
>> The Demand method skips the call stack frame for the method from which it
>> is
>> called. In order to have your assembly included in the stack walk
>> initiated
>> by Demand, you'll need to move it into a separate method since the Main
>> method has no within-assembly callers. e.g.:
>>
>> static void Main(string[] args)
>> {
>>     DemandFileIOPermission();
>>     FileStream fw = new FileStream("c:\\hello.txt", FileMode.Create);
>> }
>>
>> private static void DemandFileIOPermission()
>> {
>>     FileIOPermission fip = new
>> FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
>>     fip.Demand();
>> }
>>
>>
>> "Itay Sandbank" <ItaySandb***@discussions.microsoft.com> wrote in message
>> news:B50075F7-3042-45F6-901E-3B295B5D191A@microsoft.com...
>> > Hi.
>> >
>> > I'm trying to understand how to use CAS, and found something strange.
>> > I'm
>> > trying to deny my program of a few permissions to see what happens. I
>> > created
>> > a small program that creates the file c:\hello.txt and exits:
>> >
>> > [assembly: FileIOPermission(SecurityAction.RequestRefuse,
>> > ViewAndModify="c:\\")]
>> > namespace CodeAccessSecurity
>> > {
>> >    class Program
>> >    {
>> >        static void Main(string[] args)
>> >        {
>> >            FileIOPermission fip = new
>> > FileIOPermission(FileIOPermissionAccess.AllAccess, "c:\\hello.txt");
>> >            fip.Demand();
>> >            FileStream fw = new FileStream("c:\\hello.txt",
>> > FileMode.Create);
>> >        }
>> >    }
>> > }
>> >
>> > When I run it, I see a SecurityException thrown, as can be expected.
>> > However, it is thrown when I create the FileStream and not when I
>> > Demand
>> > the
>> > FileIOPermission.
>> >
>> > When running from the local intranet zone (I changed the debugger's
>> > security settings), the exception is thrown on the Demand - as I
>> > expected
>> > in
>> > the first place.
>> >
>> > What's going on here?
>> >
>> > Thanks,
>> > Itay.
>>
>>