Reference docs don't define what happens if you call krb5_realm_compare() with

malformed krb5_principal structures.  Define a behavior which keeps it from

crashing if applications don't check ahead of time.

--- krb5/src/lib/krb5/krb/princ_comp.c

+++ krb5/src/lib/krb5/krb/princ_comp.c

@@ -41,6 +41,10 @@ realm_compare_flags(krb5_context context

     const krb5_data *realm1 = &princ1->realm;

     const krb5_data *realm2 = &princ2->realm;

+    if (princ1 == NULL || princ2 == NULL)

+        return FALSE;

+    if (realm1 == NULL || realm2 == NULL)

+        return FALSE;

     if (realm1->length != realm2->length)

         return FALSE;

     if (realm1->length == 0)

@@ -92,6 +98,9 @@ krb5_principal_compare_flags(krb5_contex

     krb5_principal upn2 = NULL;

     krb5_boolean ret = FALSE;

+    if (princ1 == NULL || princ2 == NULL)

+        return FALSE;

+

     if (flags & KRB5_PRINCIPAL_COMPARE_ENTERPRISE) {

         /* Treat UPNs as if they were real principals */

         if (princ1->type == KRB5_NT_ENTERPRISE_PRINCIPAL) {