CVE-2022-2031 gensec_krb5: Add helper function to check if client sent an initial ticket

This will be used in the kpasswd service to ensure that the client has
an initial ticket to kadmin/changepw, and not a service ticket.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15047
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15049

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>

5 files changed, 157 insertions, 18 deletions

diff --git a/source4/auth/gensec/gensec_krb5.c b/source4/auth/gensec/gensec_krb5.c
index 7d87b3ac6b9..104e4639c44 100644
--- a/source4/auth/gensec/gensec_krb5.c
+++ b/source4/auth/gensec/gensec_krb5.c
@@ -44,27 +44,11 @@
 #include "../lib/util/asn1.h"
 #include "auth/kerberos/pac_utils.h"
 #include "gensec_krb5.h"
+#include "gensec_krb5_internal.h"
+#include "gensec_krb5_helpers.h"
 
 _PUBLIC_ NTSTATUS gensec_krb5_init(TALLOC_CTX *);
 
-enum GENSEC_KRB5_STATE {
-	GENSEC_KRB5_SERVER_START,
-	GENSEC_KRB5_CLIENT_START,
-	GENSEC_KRB5_CLIENT_MUTUAL_AUTH,
-	GENSEC_KRB5_DONE
-};
-
-struct gensec_krb5_state {
-	enum GENSEC_KRB5_STATE state_position;
-	struct smb_krb5_context *smb_krb5_context;
-	krb5_auth_context auth_context;
-	krb5_data enc_ticket;
-	krb5_keyblock *keyblock;
-	krb5_ticket *ticket;
-	bool gssapi;
-	krb5_flags ap_req_options;
-};
-
 static int gensec_krb5_destroy(struct gensec_krb5_state *gensec_krb5_state)
 {
 	if (!gensec_krb5_state->smb_krb5_context) {
diff --git a/source4/auth/gensec/gensec_krb5_helpers.c b/source4/auth/gensec/gensec_krb5_helpers.c
new file mode 100644
index 00000000000..21f2f1e884e
--- /dev/null
+++ b/source4/auth/gensec/gensec_krb5_helpers.c
@@ -0,0 +1,72 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   Kerberos backend for GENSEC
+
+   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2004
+   Copyright (C) Andrew Tridgell 2001
+   Copyright (C) Luke Howard 2002-2003
+   Copyright (C) Stefan Metzmacher 2004-2005
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+#include "auth/auth.h"
+#include "auth/gensec/gensec.h"
+#include "auth/gensec/gensec_internal.h"
+#include "gensec_krb5_internal.h"
+#include "gensec_krb5_helpers.h"
+#include "system/kerberos.h"
+#include "auth/kerberos/kerberos.h"
+
+static struct gensec_krb5_state *get_private_state(const struct gensec_security *gensec_security)
+{
+	struct gensec_krb5_state *gensec_krb5_state = NULL;
+
+	if (strcmp(gensec_security->ops->name, "krb5") != 0) {
+		/* We require that the krb5 mechanism is being used. */
+		return NULL;
+	}
+
+	gensec_krb5_state = talloc_get_type(gensec_security->private_data,
+					    struct gensec_krb5_state);
+	return gensec_krb5_state;
+}
+
+/*
+ * Returns 1 if our ticket has the initial flag set, 0 if not, and -1 in case of
+ * error.
+ */
+int gensec_krb5_initial_ticket(const struct gensec_security *gensec_security)
+{
+	struct gensec_krb5_state *gensec_krb5_state = NULL;
+
+	gensec_krb5_state = get_private_state(gensec_security);
+	if (gensec_krb5_state == NULL) {
+		return -1;
+	}
+
+	if (gensec_krb5_state->ticket == NULL) {
+		/* We don't have a ticket */
+		return -1;
+	}
+
+#ifdef SAMBA4_USES_HEIMDAL
+	return gensec_krb5_state->ticket->ticket.flags.initial;
+#else /* MIT KERBEROS */
+	return (gensec_krb5_state->ticket->enc_part2->flags & TKT_FLG_INITIAL) ? 1 : 0;
+#endif /* SAMBA4_USES_HEIMDAL */
+}
diff --git a/source4/auth/gensec/gensec_krb5_helpers.h b/source4/auth/gensec/gensec_krb5_helpers.h
new file mode 100644
index 00000000000..d7b694dad0c
--- /dev/null
+++ b/source4/auth/gensec/gensec_krb5_helpers.h
@@ -0,0 +1,32 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   Kerberos backend for GENSEC
+
+   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2004
+   Copyright (C) Andrew Tridgell 2001
+   Copyright (C) Luke Howard 2002-2003
+   Copyright (C) Stefan Metzmacher 2004-2005
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+struct gensec_security;
+
+/*
+ * Returns 1 if our ticket has the initial flag set, 0 if not, and -1 in case of
+ * error.
+ */
+int gensec_krb5_initial_ticket(const struct gensec_security *gensec_security);
diff --git a/source4/auth/gensec/gensec_krb5_internal.h b/source4/auth/gensec/gensec_krb5_internal.h
new file mode 100644
index 00000000000..0bb796f1b2a
--- /dev/null
+++ b/source4/auth/gensec/gensec_krb5_internal.h
@@ -0,0 +1,47 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   Kerberos backend for GENSEC
+
+   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2004
+   Copyright (C) Andrew Tridgell 2001
+   Copyright (C) Luke Howard 2002-2003
+   Copyright (C) Stefan Metzmacher 2004-2005
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+#include "auth/gensec/gensec.h"
+#include "system/kerberos.h"
+#include "auth/kerberos/kerberos.h"
+
+enum GENSEC_KRB5_STATE {
+	GENSEC_KRB5_SERVER_START,
+	GENSEC_KRB5_CLIENT_START,
+	GENSEC_KRB5_CLIENT_MUTUAL_AUTH,
+	GENSEC_KRB5_DONE
+};
+
+struct gensec_krb5_state {
+	enum GENSEC_KRB5_STATE state_position;
+	struct smb_krb5_context *smb_krb5_context;
+	krb5_auth_context auth_context;
+	krb5_data enc_ticket;
+	krb5_keyblock *keyblock;
+	krb5_ticket *ticket;
+	bool gssapi;
+	krb5_flags ap_req_options;
+};
diff --git a/source4/auth/gensec/wscript_build b/source4/auth/gensec/wscript_build
index d14a50ff273..20271f1665b 100644
--- a/source4/auth/gensec/wscript_build
+++ b/source4/auth/gensec/wscript_build
@@ -18,6 +18,10 @@ bld.SAMBA_MODULE('gensec_krb5',
         enabled=bld.AD_DC_BUILD_IS_ENABLED()
 	)
 
+bld.SAMBA_SUBSYSTEM('gensec_krb5_helpers',
+    source='gensec_krb5_helpers.c',
+    deps='gensec_krb5',
+    enabled=bld.AD_DC_BUILD_IS_ENABLED())
 
 bld.SAMBA_MODULE('gensec_gssapi',
 	source='gensec_gssapi.c',