linux-kernel - Re: [PATCH v7 04/17] X.509: Parse Basic Constraints for CA

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Date:   Thu, 18 Nov 2021 23:29:40 +0000
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
CC:     "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
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        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jarkko Sakkinen <jarkko@...nel.org>,
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        Konrad Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v7 04/17] X.509: Parse Basic Constraints for CA



> On Nov 18, 2021, at 3:59 PM, Mimi Zohar <zohar@...ux.ibm.com> wrote:
> 
> Hi Eric,
> 
> On Mon, 2021-11-15 at 19:15 -0500, Eric Snowberg wrote:
>> Parse the X.509 Basic Constraints.  The basic constraints extension
>> identifies whether the subject of the certificate is a CA.
>> 
>> BasicConstraints ::= SEQUENCE {
>>        cA                      BOOLEAN DEFAULT FALSE,
>>        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }
>> 
>> If the CA is true, store it in a new public_key field call key_is_ca.
>> This will be used in a follow on patch that requires knowing if the
>> public key is a CA.
>> 
>> Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
>> ---
>> v7: Initial version
>> ---
>> crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
>> include/crypto/public_key.h               | 1 +
>> 2 files changed, 10 insertions(+)
>> 
>> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
>> index 6d003096b5bc..f4299b8a4926 100644
>> --- a/crypto/asymmetric_keys/x509_cert_parser.c
>> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
>> @@ -571,6 +571,15 @@ int x509_process_extension(void *context, size_t hdrlen,
>> 		return 0;
>> 	}
>> 
>> +	if (ctx->last_oid == OID_basicConstraints) {
>> +		if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
>> +			return -EBADMSG;
>> +		if (v[1] != vlen - 2)
>> +			return -EBADMSG;
>> +		if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
>> +			ctx->cert->pub->key_is_ca = true;
>> +	}
>> +
>> 	return 0;
>> }
>> 
>> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
>> index a9b2e600b7cc..61c66be80995 100644
>> --- a/include/crypto/public_key.h
>> +++ b/include/crypto/public_key.h
>> @@ -28,6 +28,7 @@ struct public_key {
>> 	bool key_is_private;
>> 	const char *id_type;
>> 	const char *pkey_algo;
>> +	bool key_is_ca;
> 
> David added "key_is_private" intentionally where he did.  Adding the
> "key_is_ca" immediately afterwards doesn't change the struct size.

Ok, I’ll change that in the next round.  Thanks.