linux-kernel - Re: [PATCH v9,1/4] X.509: Add CodeSigning extended key usage parsing

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Date:   Fri, 26 Aug 2022 23:23:00 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:     David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Ben Boeckel <me@...boeckel.net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Malte Gell <malte.gell@....de>,
        Varad Gautam <varad.gautam@...e.com>,
        Mimi Zohar <zohar@...ux.ibm.com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH v9,1/4] X.509: Add CodeSigning extended key usage parsing

On Thu, Aug 25, 2022 at 10:23:11PM +0800, Lee, Chun-Yi wrote:
> This patch adds the logic for parsing the CodeSign extended key usage

It's *not* a patch once it is applied.

And isn't the identifier actually "codeSign", not "CodeSign"? Please,
format identifier correctly in order not to cause confusion.

So, how I would rewrite the first sentence, would be:

  Add the logic for parsing codeSign extended key usage field, as
  described in RFC2459, section "4.2.1.13  Extended key usage
  field.

E.g. it took me 15 minutes to review the commit message alone
because I could not remember the RFC number off top of my head.

> extension in X.509. The parsing result will be set to the
> ext_key_usage
> flag which is carried by public key. It can be used in the PKCS#7
> verification.
> 
> Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
> ---
>  crypto/asymmetric_keys/x509_cert_parser.c | 25 +++++++++++++++++++++++
>  include/crypto/public_key.h               |  1 +
>  include/linux/oid_registry.h              |  5 +++++
>  3 files changed, 31 insertions(+)
> 
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 2899ed80bb18..1f67e0adef65 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -554,6 +554,8 @@ int x509_process_extension(void *context, size_t hdrlen,
>  	struct x509_parse_context *ctx = context;
>  	struct asymmetric_key_id *kid;
>  	const unsigned char *v = value;
> +	int i = 0;
> +	enum OID oid;

I'd reorder the declarations (suggestion).

>  
>  	pr_debug("Extension: %u\n", ctx->last_oid);
>  
> @@ -583,6 +585,29 @@ int x509_process_extension(void *context, size_t hdrlen,
>  		return 0;
>  	}
>  
> +	if (ctx->last_oid == OID_extKeyUsage) {
> +		if (vlen < 2 ||
> +		    v[0] != ((ASN1_UNIV << 6) | ASN1_CONS_BIT | ASN1_SEQ) ||
> +		    v[1] != vlen - 2)
> +			return -EBADMSG;
> +		i += 2;
> +
> +		while (i < vlen) {
> +			/* A 10 bytes EKU OID Octet blob =
> +			 * ASN1_OID + size byte + 8 bytes OID */
> +			if ((i + 10) > vlen || v[i] != ASN1_OID || v[i + 1] != 8)
> +				return -EBADMSG;
> +
> +			oid = look_up_OID(v + i + 2, v[i + 1]);
> +			if (oid == OID_codeSigning) {
> +				ctx->cert->pub->ext_key_usage |= EKU_codeSigning;
> +			}
> +			i += 10;
> +		}
> +		pr_debug("extKeyUsage: %d\n", ctx->cert->pub->ext_key_usage);
> +		return 0;
> +	}
> +
>  	return 0;
>  }
>  
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 68f7aa2a7e55..72c0fcc39d0f 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;
> +	unsigned int ext_key_usage : 9;      /* Extended Key Usage (9-bit) */
>  };
>  
>  extern void public_key_free(struct public_key *key);
> diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h
> index 0f4a8903922a..460135c2d918 100644
> --- a/include/linux/oid_registry.h
> +++ b/include/linux/oid_registry.h
> @@ -140,9 +140,14 @@ enum OID {
>  	OID_TPMImportableKey,		/* 2.23.133.10.1.4 */
>  	OID_TPMSealedData,		/* 2.23.133.10.1.5 */
>  
> +	/* Extended key purpose OIDs [RFC 5280] */
> +	OID_codeSigning,		/* 1.3.6.1.5.5.7.3.3 */
> +
>  	OID__NR
>  };
>  
> +#define EKU_codeSigning	(1 << 2)
> +
>  extern enum OID look_up_OID(const void *data, size_t datasize);
>  extern int parse_OID(const void *data, size_t datasize, enum OID *oid);
>  extern int sprint_oid(const void *, size_t, char *, size_t);
> -- 
> 2.26.2
> 

BR, Jarkko