s4:auth/kerberos: add S4U2Proxy support to kerberos_kinit_password_cc()

For S4U2Proxy we need to use the ticket from the S4U2Self stage
and ask the kdc for the delegated ticket for the target service.

metze

3 files changed, 134 insertions, 5 deletions

diff --git a/source4/auth/kerberos/kerberos.c b/source4/auth/kerberos/kerberos.c
index fa8c64b93e..d32559ed81 100644
--- a/source4/auth/kerberos/kerberos.c
+++ b/source4/auth/kerberos/kerberos.c
@@ -81,13 +81,16 @@
 
   The impersonate_principal is the principal if NULL, or the principal to impersonate
 
-  The target_service defaults to the krbtgt if NULL, but could be kpasswd/realm or the local service (if we are doing s4u2self)
+  The self_service, should be the local service (for S4U2Self if impersonate_principal is given).
+
+  The target_service defaults to the krbtgt if NULL, but could be kpasswd/realm or a remote service (for S4U2Proxy)
 
 */
  krb5_error_code kerberos_kinit_password_cc(krb5_context ctx, krb5_ccache store_cc,
 					    krb5_principal init_principal,
 					    const char *init_password,
 					    krb5_principal impersonate_principal,
+					    const char *self_service,
 					    const char *target_service,
 					    krb5_get_init_creds_opt *krb_options,
 					    time_t *expire_time, time_t *kdc_time)
@@ -96,13 +99,21 @@
 	krb5_get_creds_opt options;
 	krb5_principal store_principal;
 	krb5_creds store_creds;
-	const char *self_service = target_service;
 	krb5_creds *s4u2self_creds;
+	Ticket s4u2self_ticket;
+	size_t s4u2self_ticketlen;
+	krb5_creds *s4u2proxy_creds;
 	krb5_principal self_princ;
+	bool s4u2proxy;
+	krb5_principal target_princ;
 	krb5_ccache tmp_cc;
 	const char *self_realm;
 	krb5_principal blacklist_principal = NULL;
 
+	if (impersonate_principal && self_service == NULL) {
+		return EINVAL;
+	}
+
 	/*
 	 * If we are not impersonating, then get this ticket for the
 	 * target service, otherwise a krbtgt, and get the next ticket
@@ -168,6 +179,18 @@
 	krb5_free_cred_contents(ctx, &store_creds);
 
 	/*
+	 * Check if we also need S4U2Proxy or if S4U2Self is
+	 * enough in order to get a ticket for the target.
+	 */
+	if (target_service == NULL) {
+		s4u2proxy = false;
+	} else if (strcmp(target_service, self_service) == 0) {
+		s4u2proxy = false;
+	} else {
+		s4u2proxy = true;
+	}
+
+	/*
 	 * For S4U2Self we need our own service principal,
 	 * which belongs to our own realm (available on
 	 * our client principal).
@@ -197,6 +220,14 @@
 		return code;
 	}
 
+	if (s4u2proxy) {
+		/*
+		 * If we want S4U2Proxy, we need the forwardable flag
+		 * on the S4U2Self ticket.
+		 */
+		krb5_get_creds_opt_set_options(ctx, options, KRB5_GC_FORWARDABLE);
+	}
+
 	code = krb5_get_creds_opt_set_impersonate(ctx, options,
 						  impersonate_principal);
 	if (code != 0) {
@@ -211,6 +242,101 @@
 			      self_princ, &s4u2self_creds);
 	krb5_get_creds_opt_free(ctx, options);
 	krb5_free_principal(ctx, self_princ);
+	if (code != 0) {
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	if (!s4u2proxy) {
+		krb5_cc_destroy(ctx, tmp_cc);
+
+		/*
+		 * Now make sure we store the impersonated principal
+		 * and creds instead of the TGT related stuff
+		 * in the krb5_ccache of the caller.
+		 */
+		code = krb5_copy_creds_contents(ctx, s4u2self_creds,
+						&store_creds);
+		krb5_free_creds(ctx, s4u2self_creds);
+		if (code != 0) {
+			return code;
+		}
+
+		/*
+		 * It's important to store the principal the KDC
+		 * returned, as otherwise the caller would not find
+		 * the S4U2Self ticket in the krb5_ccache lookup.
+		 */
+		store_principal = store_creds.client;
+		goto store;
+	}
+
+	/*
+	 * We are trying S4U2Proxy:
+	 *
+	 * We need the ticket from the S4U2Self step
+	 * and our TGT in order to get the delegated ticket.
+	 */
+	code = decode_Ticket((const uint8_t *)s4u2self_creds->ticket.data,
+			     s4u2self_creds->ticket.length,
+			     &s4u2self_ticket,
+			     &s4u2self_ticketlen);
+	krb5_free_creds(ctx, s4u2self_creds);
+	if (code != 0) {
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	/*
+	 * For S4U2Proxy we also got a target service principal,
+	 * which also belongs to our own realm (available on
+	 * our client principal).
+	 */
+	code = krb5_parse_name(ctx, target_service, &target_princ);
+	if (code != 0) {
+		free_Ticket(&s4u2self_ticket);
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	code = krb5_principal_set_realm(ctx, target_princ, self_realm);
+	if (code != 0) {
+		free_Ticket(&s4u2self_ticket);
+		krb5_free_principal(ctx, target_princ);
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	code = krb5_get_creds_opt_alloc(ctx, &options);
+	if (code != 0) {
+		free_Ticket(&s4u2self_ticket);
+		krb5_free_principal(ctx, target_princ);
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	krb5_get_creds_opt_set_options(ctx, options, KRB5_GC_FORWARDABLE);
+	krb5_get_creds_opt_set_options(ctx, options, KRB5_GC_CONSTRAINED_DELEGATION);
+
+	code = krb5_get_creds_opt_set_ticket(ctx, options, &s4u2self_ticket);
+	free_Ticket(&s4u2self_ticket);
+	if (code != 0) {
+		krb5_get_creds_opt_free(ctx, options);
+		krb5_free_principal(ctx, target_princ);
+		krb5_free_principal(ctx, blacklist_principal);
+		krb5_cc_destroy(ctx, tmp_cc);
+		return code;
+	}
+
+	code = krb5_get_creds(ctx, options, tmp_cc,
+			      target_princ, &s4u2proxy_creds);
+	krb5_get_creds_opt_free(ctx, options);
+	krb5_free_principal(ctx, target_princ);
 	krb5_cc_destroy(ctx, tmp_cc);
 	if (code != 0) {
 		krb5_free_principal(ctx, blacklist_principal);
@@ -222,9 +348,9 @@
 	 * and creds instead of the TGT related stuff
 	 * in the krb5_ccache of the caller.
 	 */
-	code = krb5_copy_creds_contents(ctx, s4u2self_creds,
+	code = krb5_copy_creds_contents(ctx, s4u2proxy_creds,
 					&store_creds);
-	krb5_free_creds(ctx, s4u2self_creds);
+	krb5_free_creds(ctx, s4u2proxy_creds);
 	if (code != 0) {
 		krb5_free_principal(ctx, blacklist_principal);
 		return code;
diff --git a/source4/auth/kerberos/kerberos.h b/source4/auth/kerberos/kerberos.h
index c712569e5d..31794b8e03 100644
--- a/source4/auth/kerberos/kerberos.h
+++ b/source4/auth/kerberos/kerberos.h
@@ -97,7 +97,9 @@ krb5_error_code ads_krb5_mk_req(krb5_context context,
 bool get_auth_data_from_tkt(TALLOC_CTX *mem_ctx, DATA_BLOB *auth_data, krb5_ticket *tkt);
 krb5_error_code kerberos_kinit_password_cc(krb5_context ctx, krb5_ccache cc,
 					   krb5_principal principal, const char *password,
-					   krb5_principal impersonate_principal, const char *target_service,
+					   krb5_principal impersonate_principal,
+					   const char *self_service,
+					   const char *target_service,
 					   krb5_get_init_creds_opt *krb_options,
 					   time_t *expire_time, time_t *kdc_time);
 krb5_error_code kerberos_kinit_keyblock_cc(krb5_context ctx, krb5_ccache cc,
diff --git a/source4/auth/kerberos/kerberos_util.c b/source4/auth/kerberos/kerberos_util.c
index 9cef977306..9a48e95c6d 100644
--- a/source4/auth/kerberos/kerberos_util.c
+++ b/source4/auth/kerberos/kerberos_util.c
@@ -408,6 +408,7 @@ krb5_error_code principal_from_credentials(TALLOC_CTX *parent_ctx,
 							 princ, password,
 							 impersonate_principal,
 							 self_service,
+							 target_service,
 							 krb_options,
 							 NULL, &kdc_time);
 		} else if (impersonate_principal) {