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Message-ID: <ea42a31d-f62e-83e0-f66c-215d8b27b5ad@linux.ibm.com>
Date:   Tue, 8 Mar 2022 08:56:57 -0500
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Subject: Re: [PATCH 3/4] KEYS: CA link restriction
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To:     Mimi Zohar <zohar@linux.ibm.com>,
        Eric Snowberg <eric.snowberg@oracle.com>
Cc:     Jarkko Sakkinen <jarkko@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "dwmw2@infradead.org" <dwmw2@infradead.org>,
        "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "jmorris@namei.org" <jmorris@namei.org>,
        "serge@hallyn.com" <serge@hallyn.com>,
        "nayna@linux.ibm.com" <nayna@linux.ibm.com>,
        "mic@linux.microsoft.com" <mic@linux.microsoft.com>,
        Konrad Wilk <konrad.wilk@oracle.com>,
        "keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>
References: <20220301173651.3435350-1-eric.snowberg@oracle.com>
 <20220301173651.3435350-4-eric.snowberg@oracle.com>
 <47f3654e-892d-a35a-e77c-70ada1ebcf43@linux.ibm.com>
 <2415444C-AD8F-4F03-8B1C-C0770F83ADAE@oracle.com>
 <e2dd58cd6074ae692256333b43b5ecde70bcdbdd.camel@linux.ibm.com>
 <67456A73-8B72-4DB6-8E23-7C603661A0A4@oracle.com>
 <22860730-d615-5683-6af0-05b6f4f3e71d@linux.ibm.com>
 <e10f2161aaa69a9d301b3a16a37cbab266318aee.camel@linux.ibm.com>
From:   Stefan Berger <stefanb@linux.ibm.com>
In-Reply-To: <e10f2161aaa69a9d301b3a16a37cbab266318aee.camel@linux.ibm.com>
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On 3/8/22 07:45, Mimi Zohar wrote:
> On Mon, 2022-03-07 at 21:31 -0500, Stefan Berger wrote:
>>
>> On 3/7/22 18:38, Eric Snowberg wrote:
>>>
>>>
>>>> On Mar 7, 2022, at 4:01 PM, Mimi Zohar <zohar@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.
>>>
>> 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;
> 
> Agreed, as long as the other two criteria are also met: CA and keyUsage
> should be required and limited to keyCertSign.

right, it's not as easy as the return statement above...

> 
> thanks,
> 
> Mimi
>