[PATCH 3/4] KEYS: CA link restriction

[Eric Snowberg]

> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <zohar at linux.ibm.com> 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.