Subject: Re: [GIT PULL] Keys: Set 4 - Key ACLs for 5.3

From: Mimi Zohar <[email-masked]>
Date: Wed, 21 Aug 2019 11:43:23 -0400

On Fri, 2019-08-16 at 14:36 +0100, David Howells wrote:
> Mimi Zohar <[email-masked]> wrote:
> 
> > Sorry for the delay.  An exception is needed for loading builtin keys
> > "KEY_ALLOC_BUILT_IN" onto a keyring that is not writable by userspace.
> >  The following works, but probably is not how David would handle the
> > exception.
> 
> I think the attached is the right way to fix it.
> 
> load_system_certificate_list(), for example, when it creates keys does this:
> 
> 	key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),
> 
> marking the keyring as "possessed" in make_key_ref().  This allows the
> possessor permits to be used - and that's the *only* way to use them for
> internal keyrings like this because you can't link to them and you can't join
> them.

In addition, as long as additional keys still can't be added or
existing keys updated by userspace on the .builtin_trusted_keys, then
this is fine.

> 
> David
> ---
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index 57be78b5fdfc..1f8f26f7bb05 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -99,7 +99,7 @@ static __init int system_trusted_keyring_init(void)
>  	builtin_trusted_keys =
>  		keyring_alloc(".builtin_trusted_keys",
>  			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
> -			      &internal_key_acl, KEY_ALLOC_NOT_IN_QUOTA,
> +			      &internal_keyring_acl, KEY_ALLOC_NOT_IN_QUOTA,
>  			      NULL, NULL);
>  	if (IS_ERR(builtin_trusted_keys))
>  		panic("Can't allocate builtin trusted keyring\n");
> diff --git a/security/keys/permission.c b/security/keys/permission.c
> index fc84d9ef6239..86efd3eaf083 100644
> --- a/security/keys/permission.c
> +++ b/security/keys/permission.c
> @@ -47,7 +47,7 @@ struct key_acl internal_keyring_acl = {
>  	.usage	= REFCOUNT_INIT(1),
>  	.nr_ace	= 2,
>  	.aces = {
> -		KEY_POSSESSOR_ACE(KEY_ACE_SEARCH),
> +		KEY_POSSESSOR_ACE(KEY_ACE_SEARCH | KEY_ACE_WRITE),
>  		KEY_OWNER_ACE(KEY_ACE_VIEW | KEY_ACE_READ | KEY_ACE_SEARCH),
>  	}
>  };

Thanks, David.  The builtin keys are now being loaded.

Mimi