linux-kernel - Re: [PATCH] KEYS: prevent KEYCTL

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Message-ID: <20170921233416.GC89627@gmail.com>
Date:   Thu, 21 Sep 2017 16:34:16 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     keyrings@...r.kernel.org, Michael Halcrow <mhalcrow@...gle.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] KEYS: prevent KEYCTL_READ on negative key

On Tue, Sep 19, 2017 at 05:09:02PM +0100, David Howells wrote:
> Eric Biggers <ebiggers3@...il.com> wrote:
> 
> > +	if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
> > +		ret = -ENOKEY;
> > +		goto error2;
> > +	}
> 
> It might be better to do this check in key_validate().  Also, it should
> perhaps take the error from key->reject_error.
> 
> David

Putting the check in key_validate() would make lookups with KEY_LOOKUP_PARTIAL
stop returning negative keys, which would break keyctl_describe(),
keyctl_chown(), keyctl_setperm(), keyctl_set_timeout(), keyctl_get_security() on
negative keys.  I presume those are supposed to work?

Another solution would be to remove the special case from lookup_user_key()
where it can return a negative/revoked/invalidated/expired key if
KEY_LOOKUP_PARTIAL is not specified and the 'perm' mask is 0.  The only callers
it would affect are the case in question here which is clearly a bug, and the
root-only exceptions for keyctl_invalidate() and keyctl_clear().  And I suspect
the latter two are unintentional as well.  (Is root *supposed* to be able to
invalidate a negative/revoked/invalidated/expired key, or clear a
revoked/invalidated/expired keyring?)

Eric