From 749d377fa357351a7bbba51f8aae72cdf0629592 Mon Sep 17 00:00:00 2001
From: Viktor Dukhovni <viktor@twosigma.com>
Date: Tue, 5 Dec 2017 18:49:50 -0500
Subject: [PATCH] Security: Avoid NULL structure pointer member dereference

This can happen in the error path when processing malformed AS
requests with a NULL client name.  Bug originally introduced on
Fri Feb 13 09:26:01 2015 +0100 in commit:

    a873e21d7c06f22943a90a41dc733ae76799390d

    kdc: base _kdc_fast_mk_error() on krb5_mk_error_ext()

Original patch by Jeffrey Altman <jaltman@secure-endpoints.com>

(cherry picked from commit 1a6a6e462dc2ac6111f9e02c6852ddec4849b887)
---
 kdc/kerberos5.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kdc/kerberos5.c b/kdc/kerberos5.c
index 95a74927f7..675b406b82 100644
--- a/kdc/kerberos5.c
+++ b/kdc/kerberos5.c
@@ -2226,15 +2226,17 @@ _kdc_as_rep(kdc_request_t r,
     /*
      * In case of a non proxy error, build an error message.
      */
-    if(ret != 0 && ret != HDB_ERR_NOT_FOUND_HERE && reply->length == 0) {
+    if (ret != 0 && ret != HDB_ERR_NOT_FOUND_HERE && reply->length == 0) {
 	ret = _kdc_fast_mk_error(context, r,
 				 &error_method,
 				 r->armor_crypto,
 				 &req->req_body,
 				 ret, r->e_text,
 				 r->server_princ,
-				 &r->client_princ->name,
-				 &r->client_princ->realm,
+				 r->client_princ ?
+                                     &r->client_princ->name : NULL,
+				 r->client_princ ?
+                                     &r->client_princ->realm : NULL,
 				 NULL, NULL,
 				 reply);
 	if (ret)