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