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From 4b330d5be1f8048be4d079ac3cb38d60c0e99e69 Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Wed, 4 Nov 2015 21:28:28 -0500
Subject: Fix IAKERB context export/import [CVE-2015-2698]

The patches for CVE-2015-2696 contained a regression in the newly
added IAKERB iakerb_gss_export_sec_context() function, which could
cause it to corrupt memory.  Fix the regression by properly
dereferencing the context_handle pointer before casting it.

Also, the patches did not implement an IAKERB gss_import_sec_context()
function, under the erroneous belief than an exported IAKERB context
would be tagged as a krb5 context.  Implement it now to allow IAKERB
contexts to be successfully exported and imported after establishment.

CVE-2015-2698:

In any MIT krb5 release with the patches for CVE-2015-2696 applied, an
application which calls gss_export_sec_context() may experience memory
corruption if the context was established using the IAKERB mechanism.
Historically, some vulnerabilities of this nature can be translated
into remote code execution, though the necessary exploits must be
tailored to the individual application and are usually quite
complicated.

    CVSSv2 Vector: AV:N/AC:H/Au:S/C:C/I:C/A:C/E:POC/RL:OF/RC:C

ticket: 8273 (new)
target_version: 1.14
tags: pullup

(cherry picked from commit d8b31c874c7d1039be7649362ef11c89f4e14c27)

Patch-Category: upstream
---
 src/lib/gssapi/krb5/gssapiP_krb5.h |  5 +++++
 src/lib/gssapi/krb5/gssapi_krb5.c  |  2 +-
 src/lib/gssapi/krb5/iakerb.c       | 42 +++++++++++++++++++++++++++++++-------
 3 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/src/lib/gssapi/krb5/gssapiP_krb5.h b/src/lib/gssapi/krb5/gssapiP_krb5.h
index 05dc321..ac53662 100644
--- a/src/lib/gssapi/krb5/gssapiP_krb5.h
+++ b/src/lib/gssapi/krb5/gssapiP_krb5.h
@@ -1396,6 +1396,11 @@ OM_uint32 KRB5_CALLCONV
 iakerb_gss_export_sec_context(OM_uint32 *minor_status,
                               gss_ctx_id_t *context_handle,
                               gss_buffer_t interprocess_token);
+
+OM_uint32 KRB5_CALLCONV
+iakerb_gss_import_sec_context(OM_uint32 *minor_status,
+                              const gss_buffer_t interprocess_token,
+                              gss_ctx_id_t *context_handle);
 #endif /* LEAN_CLIENT */
 
 OM_uint32 KRB5_CALLCONV
diff --git a/src/lib/gssapi/krb5/gssapi_krb5.c b/src/lib/gssapi/krb5/gssapi_krb5.c
index 9a23656..d7ba279 100644
--- a/src/lib/gssapi/krb5/gssapi_krb5.c
+++ b/src/lib/gssapi/krb5/gssapi_krb5.c
@@ -945,7 +945,7 @@ static struct gss_config iakerb_mechanism = {
     NULL,
 #else
     iakerb_gss_export_sec_context,
-    NULL,
+    iakerb_gss_import_sec_context,
 #endif
     krb5_gss_inquire_cred_by_mech,
     krb5_gss_inquire_names_for_mech,
diff --git a/src/lib/gssapi/krb5/iakerb.c b/src/lib/gssapi/krb5/iakerb.c
index e25862d..32a341e 100644
--- a/src/lib/gssapi/krb5/iakerb.c
+++ b/src/lib/gssapi/krb5/iakerb.c
@@ -1057,7 +1057,7 @@ iakerb_gss_export_sec_context(OM_uint32 *minor_status,
                               gss_buffer_t interprocess_token)
 {
     OM_uint32 maj;
-    iakerb_ctx_id_t ctx = (iakerb_ctx_id_t)context_handle;
+    iakerb_ctx_id_t ctx = (iakerb_ctx_id_t)*context_handle;
 
     /* We don't currently support exporting partially established contexts. */
     if (!ctx->established)
@@ -1072,13 +1072,41 @@ iakerb_gss_export_sec_context(OM_uint32 *minor_status,
     return maj;
 }
 
-/*
- * Until we implement partial context exports, there are no IAKERB exported
- * context tokens, only tokens for the underlying krb5 context.  So we do not
- * need to implement an iakerb_gss_import_sec_context() yet; it would be
- * unreachable except via a manually constructed token.
- */
+OM_uint32 KRB5_CALLCONV
+iakerb_gss_import_sec_context(OM_uint32 *minor_status,
+                              gss_buffer_t interprocess_token,
+                              gss_ctx_id_t *context_handle)
+{
+    OM_uint32 maj, tmpmin;
+    krb5_error_code code;
+    gss_ctx_id_t gssc;
+    krb5_gss_ctx_id_t kctx;
+    iakerb_ctx_id_t ctx;
+
+    maj = krb5_gss_import_sec_context(minor_status, interprocess_token, &gssc);
+    if (maj != GSS_S_COMPLETE)
+        return maj;
+    kctx = (krb5_gss_ctx_id_t)gssc;
+
+    if (!kctx->established) {
+        /* We don't currently support importing partially established
+         * contexts. */
+        krb5_gss_delete_sec_context(&tmpmin, &gssc, GSS_C_NO_BUFFER);
+        return GSS_S_FAILURE;
+    }
 
+    code = iakerb_alloc_context(&ctx, kctx->initiate);
+    if (code != 0) {
+        krb5_gss_delete_sec_context(&tmpmin, &gssc, GSS_C_NO_BUFFER);
+        *minor_status = code;
+        return GSS_S_FAILURE;
+    }
+
+    ctx->gssc = gssc;
+    ctx->established = 1;
+    *context_handle = (gss_ctx_id_t)ctx;
+    return GSS_S_COMPLETE;
+}
 #endif /* LEAN_CLIENT */
 
 OM_uint32 KRB5_CALLCONV
