krb5 commit: Add client_aware_channel_bindings option
Greg Hudson
ghudson at mit.edu
Wed May 20 16:58:24 EDT 2020
https://github.com/krb5/krb5/commit/225e6ef7f021cd1a8ef2a054af0ca58b7288fd81
commit 225e6ef7f021cd1a8ef2a054af0ca58b7288fd81
Author: Isaac Boukris <iboukris at gmail.com>
Date: Tue Mar 10 13:13:17 2020 +0100
Add client_aware_channel_bindings option
Add client support for KERB_AP_OPTIONS_CBT in the form of a profile
option "client_aware_gss_bindings". Adjust the make_etype_list()
helper so that enctype negotiation and AP_OPTIONS can be included in
the same IF-RELEVANT wrapper.
[ghudson at mit.edu: refactored; edited documentation; wrote commit
message]
ticket: 8900
doc/admin/conf_files/krb5_conf.rst | 6 ++
src/include/k5-int.h | 1 +
src/lib/krb5/krb/mk_req_ext.c | 165 ++++++++++++++++++-----------------
3 files changed, 92 insertions(+), 80 deletions(-)
diff --git a/doc/admin/conf_files/krb5_conf.rst b/doc/admin/conf_files/krb5_conf.rst
index 1d2aa7f..1d8ffc1 100644
--- a/doc/admin/conf_files/krb5_conf.rst
+++ b/doc/admin/conf_files/krb5_conf.rst
@@ -383,6 +383,12 @@ The libdefaults section may contain any of the following relations:
credentials will fail if the client machine does not have a
keytab. The default value is false.
+**client_aware_channel_bindings**
+ If this flag is true, then all application protocol authentication
+ requests will be flagged to indicate that the application supports
+ channel bindings when operating over a secure channel. The
+ default value is false.
+
.. _realms:
[realms]
diff --git a/src/include/k5-int.h b/src/include/k5-int.h
index 99350a8..f50cee7 100644
--- a/src/include/k5-int.h
+++ b/src/include/k5-int.h
@@ -298,6 +298,7 @@ typedef unsigned char u_char;
#define KRB5_CONF_V4_INSTANCE_CONVERT "v4_instance_convert"
#define KRB5_CONF_V4_REALM "v4_realm"
#define KRB5_CONF_VERIFY_AP_REQ_NOFAIL "verify_ap_req_nofail"
+#define KRB5_CONF_CLIENT_AWARE_GSS_BINDINGS "client_aware_channel_bindings"
/* Cache configuration variables */
#define KRB5_CC_CONF_FAST_AVAIL "fast_avail"
diff --git a/src/lib/krb5/krb/mk_req_ext.c b/src/lib/krb5/krb/mk_req_ext.c
index 9fc6a0e..0850486 100644
--- a/src/lib/krb5/krb/mk_req_ext.c
+++ b/src/lib/krb5/krb/mk_req_ext.c
@@ -68,10 +68,9 @@
*/
static krb5_error_code
-make_etype_list(krb5_context context,
- krb5_enctype *desired_etypes,
- krb5_enctype tkt_enctype,
- krb5_authdata ***authdata);
+make_ap_authdata(krb5_context context, krb5_enctype *desired_enctypes,
+ krb5_enctype tkt_enctype, krb5_boolean client_aware_cb,
+ krb5_authdata ***authdata_out);
static krb5_error_code
generate_authenticator(krb5_context,
@@ -263,7 +262,8 @@ generate_authenticator(krb5_context context, krb5_authenticator *authent,
krb5_enctype tkt_enctype)
{
krb5_error_code retval;
- krb5_authdata **ext_authdata = NULL;
+ krb5_authdata **ext_authdata = NULL, **ap_authdata, **combined;
+ int client_aware_cb;
authent->client = client;
authent->checksum = cksum;
@@ -297,99 +297,104 @@ generate_authenticator(krb5_context context, krb5_authenticator *authent,
krb5_free_authdata(context, ext_authdata);
}
- /* Only send EtypeList if we prefer another enctype to tkt_enctype */
- if (desired_etypes != NULL && desired_etypes[0] != tkt_enctype) {
- TRACE_MK_REQ_ETYPES(context, desired_etypes);
- retval = make_etype_list(context, desired_etypes, tkt_enctype,
- &authent->authorization_data);
+ retval = profile_get_boolean(context->profile, KRB5_CONF_LIBDEFAULTS,
+ KRB5_CONF_CLIENT_AWARE_GSS_BINDINGS, NULL,
+ FALSE, &client_aware_cb);
+ if (retval)
+ return retval;
+
+ /* Add etype negotiation or channel-binding awareness authdata to the
+ * front, if appropriate. */
+ retval = make_ap_authdata(context, desired_etypes, tkt_enctype,
+ client_aware_cb, &ap_authdata);
+ if (retval)
+ return retval;
+ if (ap_authdata != NULL) {
+ retval = krb5_merge_authdata(context, ap_authdata,
+ authent->authorization_data, &combined);
+ krb5_free_authdata(context, ap_authdata);
if (retval)
return retval;
+ krb5_free_authdata(context, authent->authorization_data);
+ authent->authorization_data = combined;
}
return(krb5_us_timeofday(context, &authent->ctime, &authent->cusec));
}
-/* RFC 4537 */
+/* Set *out to a DER-encoded RFC 4537 etype list, or to NULL if no etype list
+ * should be sent. */
static krb5_error_code
-make_etype_list(krb5_context context,
- krb5_enctype *desired_etypes,
- krb5_enctype tkt_enctype,
- krb5_authdata ***authdata)
+make_etype_list(krb5_context context, krb5_enctype *desired_enctypes,
+ krb5_enctype tkt_enctype, krb5_data **out)
{
- krb5_error_code code;
- krb5_etype_list etypes;
- krb5_data *enc_etype_list;
- krb5_data *ad_if_relevant;
- krb5_authdata *etype_adata[2], etype_adatum, **adata;
- int i;
-
- etypes.etypes = desired_etypes;
-
- for (etypes.length = 0;
- etypes.etypes[etypes.length] != ENCTYPE_NULL;
- etypes.length++)
- {
- /*
- * RFC 4537:
- *
- * If the enctype of the ticket session key is included in the enctype
- * list sent by the client, it SHOULD be the last on the list;
- */
- if (etypes.length && etypes.etypes[etypes.length - 1] == tkt_enctype)
- break;
- }
-
- code = encode_krb5_etype_list(&etypes, &enc_etype_list);
- if (code) {
- return code;
- }
+ krb5_etype_list etlist;
+ int count;
- etype_adatum.magic = KV5M_AUTHDATA;
- etype_adatum.ad_type = KRB5_AUTHDATA_ETYPE_NEGOTIATION;
- etype_adatum.length = enc_etype_list->length;
- etype_adatum.contents = (krb5_octet *)enc_etype_list->data;
+ *out = NULL;
- etype_adata[0] = &etype_adatum;
- etype_adata[1] = NULL;
+ /* Only send a list if we prefer another enctype to tkt_enctype. */
+ if (desired_enctypes == NULL || desired_enctypes[0] == tkt_enctype)
+ return 0;
- /* Wrap in AD-IF-RELEVANT container */
- code = encode_krb5_authdata(etype_adata, &ad_if_relevant);
- if (code) {
- krb5_free_data(context, enc_etype_list);
- return code;
+ /* Count elements of desired_etypes, stopping at tkt_enctypes if present.
+ * (Per RFC 4537, it must be the last option if it is included.) */
+ for (count = 0; desired_enctypes[count] != ENCTYPE_NULL; count++) {
+ if (count > 0 && desired_enctypes[count - 1] == tkt_enctype)
+ break;
}
- krb5_free_data(context, enc_etype_list);
-
- adata = *authdata;
- if (adata == NULL) {
- adata = (krb5_authdata **)calloc(2, sizeof(krb5_authdata *));
- i = 0;
- } else {
- for (i = 0; adata[i] != NULL; i++)
- ;
+ etlist.etypes = desired_enctypes;
+ etlist.length = count;
+ return encode_krb5_etype_list(&etlist, out);
+}
- adata = (krb5_authdata **)realloc(*authdata,
- (i + 2) * sizeof(krb5_authdata *));
- }
- if (adata == NULL) {
- krb5_free_data(context, ad_if_relevant);
- return ENOMEM;
+/* Set *authdata_out to appropriate authenticator authdata for the request,
+ * encoded in a single AD_IF_RELEVANT element. */
+static krb5_error_code
+make_ap_authdata(krb5_context context, krb5_enctype *desired_enctypes,
+ krb5_enctype tkt_enctype, krb5_boolean client_aware_cb,
+ krb5_authdata ***authdata_out)
+{
+ krb5_error_code ret;
+ krb5_authdata etypes_ad, flags_ad, *list[3];
+ krb5_data *der_etypes = NULL;
+ size_t count = 0;
+ uint8_t flagbuf[4];
+ const uint32_t KERB_AP_OPTIONS_CBT = 0x4000;
+
+ *authdata_out = NULL;
+
+ /* Include an ETYPE_NEGOTIATION element if appropriate. */
+ ret = make_etype_list(context, desired_enctypes, tkt_enctype, &der_etypes);
+ if (ret)
+ goto cleanup;
+ if (der_etypes != NULL) {
+ etypes_ad.magic = KV5M_AUTHDATA;
+ etypes_ad.ad_type = KRB5_AUTHDATA_ETYPE_NEGOTIATION;
+ etypes_ad.length = der_etypes->length;
+ etypes_ad.contents = (uint8_t *)der_etypes->data;
+ list[count++] = &etypes_ad;
}
- *authdata = adata;
- adata[i] = (krb5_authdata *)malloc(sizeof(krb5_authdata));
- if (adata[i] == NULL) {
- krb5_free_data(context, ad_if_relevant);
- return ENOMEM;
+ /* Include an AP_OPTIONS element if the CBT flag is configured. */
+ if (client_aware_cb != 0) {
+ store_32_le(KERB_AP_OPTIONS_CBT, flagbuf);
+ flags_ad.magic = KV5M_AUTHDATA;
+ flags_ad.ad_type = KRB5_AUTHDATA_AP_OPTIONS;
+ flags_ad.length = 4;
+ flags_ad.contents = flagbuf;
+ list[count++] = &flags_ad;
}
- adata[i]->magic = KV5M_AUTHDATA;
- adata[i]->ad_type = KRB5_AUTHDATA_IF_RELEVANT;
- adata[i]->length = ad_if_relevant->length;
- adata[i]->contents = (krb5_octet *)ad_if_relevant->data;
- free(ad_if_relevant); /* contents owned by adata[i] */
- adata[i + 1] = NULL;
+ if (count > 0) {
+ list[count] = NULL;
+ ret = krb5_encode_authdata_container(context,
+ KRB5_AUTHDATA_IF_RELEVANT,
+ list, authdata_out);
+ }
- return 0;
+cleanup:
+ krb5_free_data(context, der_etypes);
+ return ret;
}
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