Re: [PATCH 1/4] X.509: Add CodeSigning extended key usage parsing

[joeyli]

Hi Jarkko,

On Thu, Jan 21, 2021 at 01:40:48AM +0200, Jarkko Sakkinen wrote:
> On Wed, Jan 20, 2021 at 05:05:14PM +0800, Lee, Chun-Yi wrote:
> > This patch adds the logic for parsing the CodeSign extended key usage
> > extension in X.509. The parsing result will be set to the eku flag
> > which is carried by public key. It can be used in the PKCS#7
> > verification.
> > 
> > Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx>
> > ---
> >  crypto/asymmetric_keys/x509_cert_parser.c | 24 ++++++++++++++++++++++++
> >  include/crypto/public_key.h               |  1 +
> >  include/linux/oid_registry.h              |  5 +++++
> >  3 files changed, 30 insertions(+)
> > 
> > diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> > index 52c9b455fc7d..65721313b265 100644
> > --- a/crypto/asymmetric_keys/x509_cert_parser.c
> > +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> > @@ -497,6 +497,8 @@ 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;
> >  
> >  	pr_debug("Extension: %u\n", ctx->last_oid);
> >  
> > @@ -526,6 +528,28 @@ int x509_process_extension(void *context, size_t hdrlen,
> >  		return 0;
> >  	}
> >  
> > +	if (ctx->last_oid == OID_extKeyUsage) {
> > +		if (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 (v[i] != ASN1_OID || v[i + 1] != 8 || (i + 10) > vlen)
> > +				return -EBADMSG;
> > +
> > +			oid = look_up_OID(v + i + 2, v[i + 1]);
> > +			if (oid == OID_codeSigning) {
> > +				ctx->cert->pub->eku |= EKU_codeSigning;
> > +			}
> > +			i += 10;
> > +		}
> > +		pr_debug("extKeyUsage: %d\n", ctx->cert->pub->eku);
> 
> With eBPF around, does this make any sense?
>

I think that the dynamic debug log is still easier for checking the EKU
setting.

Thanks
Joey Lee