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" <j...@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 

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