Re: [PATCH 3/4] KEYS: CA link restriction

[Stefan Berger]

On 3/7/22 18:38, Eric Snowberg wrote:
> > On Mar 7, 2022, at 4:01 PM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote:
> >
> > On Mon, 2022-03-07 at 18:06 +0000, Eric Snowberg wrote:
> > > > > diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> > > > > index 6b1ac5f5896a..49bb2ea7f609 100644
> > > > > --- a/crypto/asymmetric_keys/restrict.c
> > > > > +++ b/crypto/asymmetric_keys/restrict.c
> > > > > @@ -108,6 +108,49 @@ int restrict_link_by_signature(struct key *dest_keyring,
> > > > > 	return ret;
> > > > > }
> > > > > +/**
> > > > > + * restrict_link_by_ca - Restrict additions to a ring of CA keys
> > > > > + * @dest_keyring: Keyring being linked to.
> > > > > + * @type: The type of key being added.
> > > > > + * @payload: The payload of the new key.
> > > > > + * @trust_keyring: Unused.
> > > > > + *
> > > > > + * Check if the new certificate is a CA. If it is a CA, then mark the new
> > > > > + * certificate as being ok to link.
> > > >
> > > > CA = root CA here, right?
> > >
> > > Yes, I’ll update the comment
> >
> > Updating the comment is not enough.  There's an existing function named
> > "x509_check_for_self_signed()" which determines whether the certificate
> > is self-signed.
>
> Originally I tried using that function.  However when the restrict link code is called,
> all the necessary x509 information is no longer available.   The code in
> restrict_link_by_ca is basically doing the equivalent to x509_check_for_self_signed.
> After verifying the cert has the CA flag set, the call to public_key_verify_signature
> validates the cert is self signed.
Isn't x509_cert_parse() being called as part of parsing the certificate? 
If so, it seems to check for a self-signed certificate every time. You 
could add something like the following to x509_check_for_self_signed(cert):
pub->x509_self_signed = cert->self_signed = true;

This could then reduce the function in 3/4 to something like:

return payload->data[asym_crypto]->x509_self_signed;


   Stefan