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

joeyli
2021-01-21T15:25:58Z

On Thu, Jan 21, 2021 at 04:32:26PM +0200, Jarkko Sakkinen wrote:
> On Thu, Jan 21, 2021 at 12:23:53PM +0800, joeyli wrote:
> > 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.
>
> Why?

There have some certificates may loaded when system boot. In booting stage,
using dynamic debug log for checking EKU is easier than eBPF.

I am not good on eBPF. Correct me if I missed anything, please!

Thanks a lot!
Joey Lee