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SubjectRe: [PATCH 07/11] keys: Move the user and user-session keyrings to the user_namespace
Date
Jann Horn <jannh@google.com> wrote:

> > + struct key *user_keyring_register;
>
> Maybe a comment about locking semantics above user_keyring_register?
> "Only written once, may be read locklessly with READ_ONCE()", or
> something like that?

Ok.

> > -
> > +#define __KDEBUG
>
> Was that supposed to be in here, or did you commit that accidentally?

Accidental.

> > - struct key *uid_keyring, *session_keyring;
> > + struct key *reg_keyring = user_ns->user_keyring_register;
>
> This is a lockless read of a field that may be written concurrently;
> this should be READ_ONCE(). (Especially on alpha, I think the memory
> ordering will actually be incorrect without READ_ONCE().)

Yeah, you're right about both of these that you pointed out. It's not needed
when the user_ns->keyring_sem is taken for writing, however.

> > + if (!IS_ERR(reg_keyring))
> > + user_ns->user_keyring_register = reg_keyring;
>
> This is a write of a pointer that may be read concurrently; this
> should be smp_store_release().

Yep.

> > + else if ((user_session = get_user_session_keyring())) {
> > + key_ref = keyring_search_aux(make_key_ref(user_session, 1),
> > + ctx);
> > if (!IS_ERR(key_ref))
> > goto found;
>
> I'm not sure I understand this code. In the "goto found" case, the
> key_put() below is skipped, right? Is that intentional?

Actually, the key_put() should be directly after the keyring_search_aux()
call, before the error check.

> > error_alloc:
> > complete_request_key(authkey, ret);
> > +error_us:
> > + key_put(user_session);
> > kleave(" = %d", ret);
> > return ret;
> > }
>
> This looks weird. If the look_up_user_keyrings() fails, user_session
> might still be an uninitialized pointer, right? And then the "goto
> error_us" jumps down here and calls key_put() on that?

The call to complete_request_key() should be after error_us and the key_put()
should be before it.

> > @@ -289,16 +291,19 @@ static int construct_get_dest_keyring(struct key **_dest_keyring)
> >
> > if (dest_keyring)
> > break;
> > + /* Fall through */
> >
> > /* fall through */
> > case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
>
> Why two "fall through" comments?

Someone else added one and when I rebased, I don't think I got a conflict.

David

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