Re: [PATCH] implement menu_lock

[phcoder <phcoder@gmail.com>]

I agree that with this design grub2 lock are somewhat cumbersome to 
implement some schemes. I would prefer a user+C-list design. In this 
case a following file be used by group
<username1>:<capability1>,<capability2>,...
<username2>:<capability1>,<capability3>,...
...
E.g.
root:all
wheel:bootnonet
...
This file can also be reversed and list users per capability instead of 
capabilities per user
Then an authentication methods would be provided in form of modules each 
one using its one configuration to match users to authentication method 
(e.g. user-hash or user-fingerprint)
To check the user level a special function would be provided
int grub_user_is_allowed (const char *id)
If user is already authenticated and is allowed to do whatever is 
specified by id it returns true, otherwise it proposes the user the list 
of available authentication methods and then calls the corresponding 
method. A drawback is that user has also to choose the method. Perhaps 
we can define methods as being non-blocking? E.g. use checkkey and so 
on. The code would be something like:
static char *
auth_user (void)
{
   int do_sleep = 100;
   for (curauth=authmethods; curauth; curauth=curauth->next)
   {
      do_sleep = min (do_sleep, curauth->sleep_max);
      curauth->init ();
   }
   while (GRUB_TERM_ASCII_CHAR (grub_getkey ()) != GRUB_TERM_ESC)
   {
    for (curauth=authmethods; curauth; curauth=curauth->next)
      if (username = curauth->check ())
	return username;
     if (do_sleep)
       grub_millisleep (do_sleep)
   }
   return 0;
}

In this case password module may be waiting for console input and 
fingerprint module would scan pci for input from fingerprint scanner
When no clist file is loaded everyone is allowed to do everything
then your menu would look like

clist.txt:
root:cmdline,barboot
user2:bazboot

passwords:
root:grubrocks
user2:grubisawesome

grub.cfg:
clist /clist.txt
passwords /passwords.txt
fingerprints /fingerprints.dat

menuentry "Anyone can boot this" {
   multiboot /foo
}

menuentry "Only users who unlocked the menu can boot this" {
   if allowed bootbar ; then
     multiboot /bar
  fi
}

menuentry "Only a few selected ones can boot this" {
   if allowed bootbaz; then
     multiboot /baz
   fi
}



Yoshinori K. Okuji wrote:
> On Sunday 10 February 2008 21:59, Robert Millan wrote:
>> I didn't see this;  it was inspired in the "lock" command in GRUB Legacy. 
>> But since it only applies to menu, and doesn't lock anything else, I
>> thought "menu_lock" would be a good choice.
>>
>> Since our default state is not to lock the menu, and that would match with
>> non-existance of the variable, I think the meaning of the variable should
>> be to lock the menu when set.  If we make it mean the opposite, e.g.
>> auth=1, what do we do when the variable is not set?
>>
>> You can observe I've been instructed by your advice not to implement ad-hoc
>> features, so I tried to avoid some generic "lock" command that would handle
>> multiple things depending on the context.  With my proposed scheme, we
>> provide the primitives and user can do just about anything.
> 
> First of all, we need an authorization status at the global level anyway, 
> because if you can enter into the command line interface, you can bypass 
> everything.
> 
> Once you accept defining an authorization status, you can write this:
> 
> menuentry "Anyone can boot this" {
>   multiboot /foo
> }
> 
> menuentry "Only users who unlocked the menu can boot this" {
>   if test $auth != no ; then
>     multiboot /bar
>   else
>     echo You must enter a password before booting this entry.
>     # Probably better to have a way to exit with an error here!
>   fi
> }
> 
> menuentry "Only a few selected ones can boot this" {
>   echo -n "Password: "
>   read password
>   if test $password = grubisawesome ; then
>     multiboot /baz
>   else
>     echo The password you entered was wrong.
>     # error error
>   fi
> }
> 
> But my feeling is that it would be more powerful to implement a password 
> checker as a command. Scripting allows you to perform many things, if GRUB 
> provides many commands and control structures, but it looks very tiring to 
> implement various features (e.g. various encryption schemes, challenge 
> retries, the translation of prompts, and so on).
> 
> Okuji
> 
> 
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-- 

Regards
Vladimir 'phcoder' Serbinenko