Require fast_req checksum to be keyed

Since the fast_req checksum is unencrypted, a keyed checksum type needs to be used.

ticket: 6461
Target_Version: 1.7
Tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22210 dc483132-0cff-0310-8789-dd5450dbe970

diff --git a/src/kdc/fast_util.c b/src/kdc/fast_util.c
index 6ced4c7e677c34de0f7f8bc2e0a3b5504c6cac82..f02410b967616715728d6ef5798c89f0f4147d3b 100644 (file)
--- a/src/kdc/fast_util.c
+++ b/src/kdc/fast_util.c
@@ -133,9 +133,11 @@ krb5_error_code  kdc_find_fast
     krb5_kdc_req *request = *requestptr;
     krb5_fast_armored_req *fast_armored_req = NULL;
     krb5_boolean cksum_valid;
+    krb5_keyblock empty_keyblock;
 
     scratch.data = NULL;
     krb5_clear_error_message(kdc_context);
+    memset(&empty_keyblock, 0, sizeof(krb5_keyblock));
     fast_padata = find_pa_data(request->padata,
                               KRB5_PADATA_FX_FAST);
     if (fast_padata !=  NULL){
@@ -192,7 +194,23 @@ krb5_error_code  kdc_find_fast
       krb5_set_error_message(kdc_context, KRB5KRB_AP_ERR_MODIFIED,
                             "FAST req_checksum invalid; request modified");
     }
-           if (retval == 0) {
+    if (retval == 0) {
+       krb5_error_code ret;
+       /* We need to confirm that a keyed checksum is used for the
+        * fast_req checksum.  In April 2009, the best way to do this is
+        * to try verifying the checksum with a keyblock with an zero
+        * length; if it succeeds, then an unkeyed checksum is used.*/
+       ret  = krb5_c_verify_checksum(kdc_context, &empty_keyblock,
+                                     KRB5_KEYUSAGE_FAST_REQ_CHKSUM,
+                                     checksummed_data, &fast_armored_req->req_checksum,
+                                     &cksum_valid);
+       if (ret == 0) {
+           retval = KRB5KDC_ERR_POLICY;
+           krb5_set_error_message(kdc_context, KRB5KDC_ERR_POLICY,
+                                  "Unkeyed checksum used in fast_req");
+       }
+    }
+    if (retval == 0) {
        if ((fast_req->fast_options & UNSUPPORTED_CRITICAL_FAST_OPTIONS) !=0)
            retval = KRB5KDC_ERR_UNKNOWN_CRITICAL_FAST_OPTION;
     }