From 75b375abcec69421c430a0241e5c72cafd96cb7f Mon Sep 17 00:00:00 2001

From: Greg Hudson <ghudson@mit.edu>

Date: Mon, 16 Jan 2017 15:09:32 -0500

Subject: [PATCH] Continue after KDC_ERR_PREAUTH_FAILED

If the KDC sends KDC_ERR_PREAUTH_FAILED, try another mechanism, or

send an unauthenticated request if optimistic preauth failed.

ticket: 8537

(cherry picked from commit 52d2de31bc4728dbc2f59c6033dcdab86da919e9)

---

 src/lib/krb5/krb/get_in_tkt.c | 45 ++++++++++++++++++++++++++++-------

 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/src/lib/krb5/krb/get_in_tkt.c b/src/lib/krb5/krb/get_in_tkt.c

index 8d0f964f9..c7d7bfe74 100644

--- a/src/lib/krb5/krb/get_in_tkt.c

+++ b/src/lib/krb5/krb/get_in_tkt.c

@@ -1308,6 +1308,7 @@ init_creds_step_request(krb5_context context,

     krb5_error_code code;

     krb5_preauthtype pa_type;

     struct errinfo save = EMPTY_ERRINFO;

+    uint32_t rcode = (ctx->err_reply == NULL) ? 0 : ctx->err_reply->error;

     if (ctx->loopcount >= MAX_IN_TKT_LOOPS) {

         code = KRB5_GET_IN_TKT_LOOP;

@@ -1358,8 +1359,10 @@ init_creds_step_request(krb5_context context,

         TRACE_INIT_CREDS_PREAUTH_MORE(context, ctx->selected_preauth_type);

         code = k5_preauth(context, ctx, ctx->more_padata, TRUE,

                           &ctx->request->padata, &pa_type);

-    } else if (ctx->err_reply != NULL &&

-               ctx->err_reply->error != KDC_ERR_PREAUTH_REQUIRED) {

+    } else if (rcode == KDC_ERR_PREAUTH_FAILED) {

+        /* Report the KDC-side failure code if we can't try another mech. */

+        code = KRB5KDC_ERR_PREAUTH_FAILED;

+    } else if (rcode && rcode != KDC_ERR_PREAUTH_REQUIRED) {

         /* Retrying after an error (possibly mechanism-specific), using error

          * padata to figure out what to change. */

         TRACE_INIT_CREDS_PREAUTH_TRYAGAIN(context, ctx->err_reply->error,

@@ -1380,7 +1383,7 @@ init_creds_step_request(krb5_context context,

     if (ctx->request->padata == NULL && ctx->method_padata != NULL) {

         /* Retrying after KDC_ERR_PREAUTH_REQUIRED, or trying again with a

-         * different mechanism after a client-side failure. */

+         * different mechanism after a failure. */

         TRACE_INIT_CREDS_PREAUTH(context);

         code = k5_preauth(context, ctx, ctx->method_padata, TRUE,

                           &ctx->request->padata, &ctx->selected_preauth_type);

@@ -1480,6 +1483,18 @@ is_referral(krb5_context context, krb5_error *err, krb5_principal client)

     return !krb5_realm_compare(context, err->client, client);

 }

+/* Transfer error padata to method data in ctx and sort it according to

+ * configuration. */

+static krb5_error_code

+accept_method_data(krb5_context context, krb5_init_creds_context ctx)

+{

+    krb5_free_pa_data(context, ctx->method_padata);

+    ctx->method_padata = ctx->err_padata;

+    ctx->err_padata = NULL;

+    return sort_krb5_padata_sequence(context, &ctx->request->client->realm,

+                                     ctx->method_padata);

+}

+

 static krb5_error_code

 init_creds_step_reply(krb5_context context,

                       krb5_init_creds_context ctx,

@@ -1538,14 +1553,26 @@ init_creds_step_reply(krb5_context context,

             ctx->restarted = FALSE;

             code = restart_init_creds_loop(context, ctx, FALSE);

         } else if (reply_code == KDC_ERR_PREAUTH_REQUIRED && retry) {

-            krb5_free_pa_data(context, ctx->method_padata);

-            ctx->method_padata = ctx->err_padata;

-            ctx->err_padata = NULL;

             note_req_timestamp(context, ctx, ctx->err_reply->stime,

                                ctx->err_reply->susec);

-            code = sort_krb5_padata_sequence(context,

-                                             &ctx->request->client->realm,

-                                             ctx->method_padata);

+            code = accept_method_data(context, ctx);

+        } else if (reply_code == KDC_ERR_PREAUTH_FAILED && retry) {

+            note_req_timestamp(context, ctx, ctx->err_reply->stime,

+                               ctx->err_reply->susec);

+            if (ctx->method_padata == NULL) {

+                /* Optimistic preauth failed on the KDC.  Allow all mechanisms

+                 * to be tried again using method data. */

+                k5_reset_preauth_types_tried(ctx);

+            } else {

+                /* Don't try again with the mechanism that failed. */

+                code = k5_preauth_note_failed(ctx, ctx->selected_preauth_type);

+                if (code)

+                    goto cleanup;

+            }

+            ctx->selected_preauth_type = KRB5_PADATA_NONE;

+            /* Accept or update method data if the KDC sent it. */

+            if (ctx->err_padata != NULL)

+                code = accept_method_data(context, ctx);

         } else if (reply_code == KDC_ERR_MORE_PREAUTH_DATA_REQUIRED && retry) {

             ctx->more_padata = ctx->err_padata;

             ctx->err_padata = NULL;