linux-kernel - Re: [PATCH 2/7] KEYS: X.509: Parse Basic Constraints for CA

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Date:   Fri, 8 Apr 2022 15:31:24 +0000
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
CC:     David Howells <dhowells@...hat.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "roberto.sassu@...wei.com" <roberto.sassu@...wei.com>,
        "nramas@...ux.microsoft.com" <nramas@...ux.microsoft.com>,
        "pvorel@...e.cz" <pvorel@...e.cz>, "tiwai@...e.de" <tiwai@...e.de>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 2/7] KEYS: X.509: Parse Basic Constraints for CA



> On Apr 8, 2022, at 8:39 AM, Mimi Zohar <zohar@...ux.ibm.com> wrote:
> 
> On Tue, 2022-04-05 at 21:53 -0400, 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 the x509_certificate.  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>
>> ---
>> crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
>> crypto/asymmetric_keys/x509_parser.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 2899ed80bb18..30f7374ea9c0 100644
>> --- a/crypto/asymmetric_keys/x509_cert_parser.c
>> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
>> @@ -583,6 +583,15 @@ int x509_process_extension(void *context, size_t hdrlen,
>> 		return 0;
>> 	}
>> 
>> +	if (ctx->last_oid == OID_basicConstraints) {
>> +		if (vlen < 2 || v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
>> +			return -EBADMSG;
>> +		if (v[1] != vlen - 2)
>> +			return -EBADMSG;
>> +		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
>> +			ctx->cert->is_root_ca = true;
>> +	}
>> +
>> 	return 0;
>> }
>> 
>> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
>> index 97a886cbe01c..dc45df9f6594 100644
>> --- a/crypto/asymmetric_keys/x509_parser.h
>> +++ b/crypto/asymmetric_keys/x509_parser.h
>> @@ -38,6 +38,7 @@ struct x509_certificate {
>> 	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
>> 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
>> 	bool		blacklisted;
>> +	bool		is_root_ca;		/* T if basic constraints CA is set */
> 
> There's no need to prefix variables with "is_".  Similar to the
> variable "self_signed" simply name this variable "root_ca".

I’ll change this name (and also the one you identified in the 3rd patch) in the next
round, thanks.