[Question][Hw4]

[anisrashidov]

Can you describe what strings stand for in Open, Read_with_capability, Execute_with_capability commands?
type command =
.
.
.
| Open of string * Object.t * permission
| Execute_with_capability of string * Object.t * string
| Read_with_capability of string * Object.t

[sujin0529]

Hi,

Please refer to comment.
If you still have questions, please let me know here again! :)

Thanks.

[anisrashidov]

Thank you. I read that. However, I still don't know exactly what it means.
In Read_with_capability command, I don't understand what "it seems that the first string is the name of capability (like 'fd' for example)." means. Can you give me an example to understand what the first string stands for?
Same applies to Execute_with_capability

[ahnjonggun]

I tried to print out the parameters of Execute_with_capability, which is string * object.t * string, in scenario 2.
Scenario2:

const enum access_control_t access_control = Capability;

void init() {
  create_subject("attacker");
  create_subject("deputy");
  create_object("secret_file");
  create_object("deputy");
  enter(Read, "attacker", "secret_file");
  enter(Execute, "attacker", "deputy");
}

void attacker() {
  int fd = open("secret_file", Read);
  execute_with_capability(fd, "deputy");
}

void deputy(int fd) { read_with_capability(fd, "secret_file"); }

My code in capability.run:

      | Execute_with_capability (str1, obj, str2) -> print_endline "execute with cap";
        print_endline str1;
        print_endline (Object.to_string obj);
        print_endline str2;

The result was

fd
deputy
fd

Since the document said that

For example, Execute_with_capability (perm, object_file, proc) will execute the target process proc with the capability perm to access object object_file

I can understand that first string being "fd" for capability, but why does the second string print out "fd" also?
I thought that it should be like "fd", "secret file" "deputy"

Thank you

[tanapthetimid]

I think the documentation is extremely misleading, and makes this homework problem confusing for no reason. for Execute_with_capability (perm, object_file, proc), perm is the string name of the file descriptor argument, so in this case the fd in execute_with_capability(fd, "deputy");, and proc is the string name of the file descriptor parameter of the object, so the fd in void deputy(int fd) {.... And object_file is the thing being executed, so it becomes the subject as well.

[anisrashidov]

Why do we need the fd parameter string?

[sujin0529]

I think this issue will answer your question.

You can think about why the file descriptor is used in capability to find the reason why the fd parameter is needed.