linux-kernel - Re: [PATCH v8 05/17] X.509: Parse Basic Constraints for CA

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Date:   Sat, 27 Nov 2021 02:43:14 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Eric Snowberg <eric.snowberg@...cle.com>, keyrings@...r.kernel.org,
        linux-integrity@...r.kernel.org, zohar@...ux.ibm.com,
        dhowells@...hat.com, dwmw2@...radead.org,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        jmorris@...ei.org, serge@...lyn.com
Cc:     keescook@...omium.org, torvalds@...ux-foundation.org,
        weiyongjun1@...wei.com, nayna@...ux.ibm.com, ebiggers@...gle.com,
        ardb@...nel.org, nramas@...ux.microsoft.com, lszubowi@...hat.com,
        jason@...c4.com, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James.Bottomley@...senPartnership.com, pjones@...hat.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH v8 05/17] X.509: Parse Basic Constraints for CA

On Tue, 2021-11-23 at 23:41 -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>

You could extend the description to state why kernel needs X.509 Basic
Constraints support.

/Jarkko

> ---
> v7: Initial version
> v8: Moved key_is_ca after key_is_private, recommended by Mimi
> ---
>  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..72dcbc06ef9c 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -26,6 +26,7 @@ struct public_key {
>         void *params;
>         u32 paramlen;
>         bool key_is_private;
> +       bool key_is_ca;
>         const char *id_type;
>         const char *pkey_algo;
>  };