krb5/SOURCES/Implement-KERB_AP_OPTIONS_CBT-server-side.patch
2021-09-09 19:45:35 +00:00

104 lines
3.9 KiB
Diff

From b37714a1b9138c0258d357931215fbd5ca7fa72b Mon Sep 17 00:00:00 2001
From: Isaac Boukris <iboukris@gmail.com>
Date: Mon, 9 Mar 2020 16:04:21 +0100
Subject: [PATCH] Implement KERB_AP_OPTIONS_CBT (server side)
Add server support for Microsoft's KERB_AP_OPTIONS_CBT as described in
MS-KILE. If the client includes the AP option in the authenticator
authdata and the server passed channel bindings, require the bindings
to match.
[ghudson@mit.edu: refactored to put more logic in the helper function;
added a comment; clarified commit message]
ticket: 8900 (new)
(cherry picked from commit 4f7c77b64a048ca5e3199b26b31493698c777a9c)
(cherry picked from commit 6407bf087fe53088d91efd09df736e979cd4e8db)
---
src/include/krb5/krb5.hin | 1 +
src/lib/gssapi/krb5/accept_sec_context.c | 45 +++++++++++++++++++++++-
2 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/src/include/krb5/krb5.hin b/src/include/krb5/krb5.hin
index f8269fb17..9264bede1 100644
--- a/src/include/krb5/krb5.hin
+++ b/src/include/krb5/krb5.hin
@@ -1915,6 +1915,7 @@ krb5_verify_checksum(krb5_context context, krb5_cksumtype ctype,
#define KRB5_AUTHDATA_SIGNTICKET 512 /**< formerly 142 in krb5 1.8 */
#define KRB5_AUTHDATA_FX_ARMOR 71
#define KRB5_AUTHDATA_AUTH_INDICATOR 97
+#define KRB5_AUTHDATA_AP_OPTIONS 143
/** @} */ /* end of KRB5_AUTHDATA group */
/* password change constants */
diff --git a/src/lib/gssapi/krb5/accept_sec_context.c b/src/lib/gssapi/krb5/accept_sec_context.c
index 9d3e2f4fe..175a24c4e 100644
--- a/src/lib/gssapi/krb5/accept_sec_context.c
+++ b/src/lib/gssapi/krb5/accept_sec_context.c
@@ -430,6 +430,32 @@ kg_process_extension(krb5_context context,
/* A zero-value channel binding, for comparison */
static const uint8_t null_cb[CB_MD5_LEN];
+/* Look for AP_OPTIONS in authdata. If present and the options include
+ * KERB_AP_OPTIONS_CBT, set *cbt_out to true. */
+static krb5_error_code
+check_cbt(krb5_context context, krb5_authdata **authdata,
+ krb5_boolean *cbt_out)
+{
+ krb5_error_code code;
+ uint32_t ad_ap_options;
+ const uint32_t KERB_AP_OPTIONS_CBT = 0x4000;
+
+ *cbt_out = FALSE;
+
+ code = krb5_find_authdata(context, NULL, authdata,
+ KRB5_AUTHDATA_AP_OPTIONS, &authdata);
+ if (code || authdata == NULL)
+ return code;
+ if (authdata[1] != NULL || authdata[0]->length != 4)
+ return KRB5KRB_AP_ERR_MSG_TYPE;
+
+ ad_ap_options = load_32_le(authdata[0]->contents);
+ if (ad_ap_options & KERB_AP_OPTIONS_CBT)
+ *cbt_out = TRUE;
+
+ return 0;
+}
+
/*
* The krb5 GSS mech appropriates the authenticator checksum field from RFC
* 4120 to store structured data instead of a checksum, indicated with checksum
@@ -454,7 +480,7 @@ process_checksum(OM_uint32 *minor_status, krb5_context context,
krb5_error_code code = 0;
OM_uint32 status, option_id, token_flags;
size_t cb_len, option_len;
- krb5_boolean valid, token_cb_present = FALSE, cb_match = FALSE;
+ krb5_boolean valid, client_cbt, token_cb_present = FALSE, cb_match = FALSE;
krb5_key subkey;
krb5_data option, empty = empty_data();
krb5_checksum cb_cksum;
@@ -582,6 +608,23 @@ process_checksum(OM_uint32 *minor_status, krb5_context context,
}
}
+ /*
+ * If the client asserts the KERB_AP_OPTIONS_CBT flag (from MS-KILE) in the
+ * authenticator authdata, and the acceptor passed channel bindings,
+ * require matching channel bindings from the client. The intent is to
+ * prevent an authenticator generated for use outside of a TLS channel from
+ * being used inside of one.
+ */
+ code = check_cbt(context, authenticator->authorization_data, &client_cbt);
+ if (code) {
+ status = GSS_S_FAILURE;
+ goto fail;
+ }
+ if (client_cbt && acceptor_cb != GSS_C_NO_CHANNEL_BINDINGS && !cb_match) {
+ status = GSS_S_BAD_BINDINGS;
+ goto fail;
+ }
+
status = GSS_S_COMPLETE;
fail: