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

joeyli
2021-01-21T04:27:26Z

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@suse.com>
> > ---
> > 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