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There are two fallacies in this noncompliant code example. First, the doPrivileged method is being called from inside the openPasswordFile method. The openPasswordFile method is privileged and returns a FileInputStream reference to its caller. This allows any caller to call openPasswordFile() directly and obtain a reference to the sensitive file due to the inherent privileges present within the corresponding code. Second, the name of the sensitive password file is user controllable which introduces other risks such as unaccounted misuse of miscellaneous sensitive files.
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import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.security.AccessController;
import java.security.PrivilegedAction;
public class Password {
public static void changePassword(String password_file) throws FileNotFoundException {
FileInputStream fin;
fin = openPasswordFile(password_file);
}
public static FileInputStream openPasswordFile(String password_file) throws FileNotFoundException {
//Declare as final and assign before the body of the anonymous inner class
//Array f[] is used to maintain language semantics while using final
final FileInputStream f[]={null};
final String file = password_file;
//Use own privilege to open the sensitive password file
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
try {
f[0] = new FileInputStream("c:\\" + file); //Perform privileged action
}catch(FileNotFoundException cnf) { System.err.println(cnf.getMessage()); }
return null; //Still mandatory to return from run()
}
});
return f[0]; //Returns a reference to privileged objects (inappropriate)
}
}
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The openPasswordFile method controls access to the sensitive password file and returns its reference. Since it cannot control being invoked by untrusted user methods, it should not assert its privileges within the body. Instead, changePassword() the caller method, can safely assert its own privilege whenever someone else calls it. This is because changePassword() does not return a reference to the sensitive file to any caller but processes the file internally. Also, since the name of the password file is hard-coded in the code, caller supplied (tainted) inputs are not used.
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import java.io.FileInputStream; import java.io.FileNotFoundException; import java.security.AccessController; import java.security.PrivilegedAction; public class Password { public static void changePassword() { //Use own privilege to open the sensitive password file final String password_file = "password"; final FileInputStream f[] = {null}; AccessController.doPrivileged(new PrivilegedAction() { public Object run() { try { f[0] = openPasswordFile(password_file); //call the privileged method here }catch(FileNotFoundException cnf) { System.err.println("Error: Operation could not be performed"); } return null; } }); //Perform other operations such as password verification } public static FileInputStream openPasswordFile(String password_file) throws FileNotFoundException { FileInputStream f = new FileInputStream("c:\\" + password_file); //Perform read/write operations on password file return f; } } |
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