linux-kernel - Re: [PATCH v10 5/9] x509: Detect sm2 keys by their parameters OID

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Message-ID: <YEJnYOvFnWr7YcJK@kernel.org>
Date:   Fri, 5 Mar 2021 19:16:16 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        davem@...emloft.net, herbert@...dor.apana.org.au,
        dhowells@...hat.com, zohar@...ux.ibm.com,
        linux-kernel@...r.kernel.org, patrick@...terwijk.org,
        linux-integrity@...r.kernel.org,
        Stefan Berger <stefanb@...ux.ibm.com>,
        Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Subject: Re: [PATCH v10 5/9] x509: Detect sm2 keys by their parameters OID

On Thu, Mar 04, 2021 at 07:51:59PM -0500, Stefan Berger wrote:
> From: Stefan Berger <stefanb@...ux.ibm.com>
> 
> Detect whether a key is an sm2 type of key by its OID in the parameters
> array rather than assuming that everything under OID_id_ecPublicKey
> is sm2, which is not the case.
> 
> Cc: David Howells <dhowells@...hat.com>
> Cc: keyrings@...r.kernel.org
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> Reviewed-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> ---
>  crypto/asymmetric_keys/x509_cert_parser.c | 12 +++++++++++-
>  include/linux/oid_registry.h              |  1 +
>  lib/oid_registry.c                        | 13 +++++++++++++
>  3 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 52c9b455fc7d..1621ceaf5c95 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -459,6 +459,7 @@ int x509_extract_key_data(void *context, size_t hdrlen,
>  			  const void *value, size_t vlen)
>  {
>  	struct x509_parse_context *ctx = context;
> +	enum OID oid;

enum is not a real type, and it is hard to recall how much it allocates
from stack. I would replace this with plain int.

>  
>  	ctx->key_algo = ctx->last_oid;
>  	switch (ctx->last_oid) {
> @@ -470,7 +471,16 @@ int x509_extract_key_data(void *context, size_t hdrlen,
>  		ctx->cert->pub->pkey_algo = "ecrdsa";
>  		break;
>  	case OID_id_ecPublicKey:
> -		ctx->cert->pub->pkey_algo = "sm2";
> +		if (parse_OID(ctx->params, ctx->params_size, &oid) != 0)
> +			return -EBADMSG;
> +
> +		switch (oid) {
> +		case OID_sm2:
> +			ctx->cert->pub->pkey_algo = "sm2";
> +			break;
> +		default:
> +			return -ENOPKG;
> +		}
>  		break;
>  	default:
>  		return -ENOPKG;
> diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h
> index b504e2f36b25..f32d91895e4d 100644
> --- a/include/linux/oid_registry.h
> +++ b/include/linux/oid_registry.h
> @@ -121,6 +121,7 @@ enum OID {
>  };
>  
>  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);
>  extern int sprint_OID(enum OID, char *, size_t);
>  
> diff --git a/lib/oid_registry.c b/lib/oid_registry.c
> index f7ad43f28579..508e0b34b5f0 100644
> --- a/lib/oid_registry.c
> +++ b/lib/oid_registry.c
> @@ -11,6 +11,7 @@
>  #include <linux/kernel.h>
>  #include <linux/errno.h>
>  #include <linux/bug.h>
> +#include <linux/asn1.h>
>  #include "oid_registry_data.c"
>  
>  MODULE_DESCRIPTION("OID Registry");
> @@ -92,6 +93,18 @@ enum OID look_up_OID(const void *data, size_t datasize)
>  }
>  EXPORT_SYMBOL_GPL(look_up_OID);
>  
> +int parse_OID(const void *data, size_t datasize, enum OID *oid)

An exported function without kdoc.

> +{
> +	const unsigned char *v = data;
> +
> +	if (datasize < 2 || v[0] != ASN1_OID || v[1] != datasize - 2)
> +		return -EBADMSG;

'1' and '2' are magic numbers unless you either have constants defining
them, or at least an inline comment with explanation.

> +
> +	*oid = look_up_OID(data + 2, datasize - 2);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(parse_OID);
> +
>  /*
>   * sprint_OID - Print an Object Identifier into a buffer
>   * @data: The encoded OID to print
> -- 
> 2.29.2
> 
> 

/Jarkko