Ticket History #5807: can't store delegated krb5 creds when using spnego

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Date: Thu, 4 Oct 2007 18:05:43 -0400
Message-Id: <200710042205.l94M5has027503@blade.boston.redhat.com>
To: krb5-bugs@mit.edu
Subject: can't find delegated krb5 creds when using spnego
From: Nalin Dahyabhai <nalin@redhat.com>
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System: Linux blade.boston.redhat.com 2.6.23-0.211.rc8.git2.fc8 #1 SMP Thu Sep 27 18:21:00 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux
Architecture: x86_64

When using SPNEGO, a client can delegate Kerberos credentials,
but gss_krb5_copy_cache() can't find them because the delegated
credential handle contains the SPNEGO mechanism OID. In this
case, the credential value is itself a union credential wrapping
the delegated Kerberos credentials.

Use Firefox's negotiate auth client with libgssapi_krb5 to
authenticate to Apache httpd with mod_auth_kerb. The server
log on my test system shows:
[Thu Oct 04 14:54:15 2007] [error] [client 172.16.80.50] Cannot store delegated credential (gss_krb5_copy_ccache: Invalid credential was supplied (No error)), referer: https://axe.boston.redhat.com/private/

This could be worked around by just passing up the delegated
credential handle in gss_accept_sec_context() when the
mechanism is SPNEGO, but teaching gss_krb5_copy_ccache() to
walk the credentials tree looked like a slightly simpler way
to go.

Index: src/lib/gssapi/mechglue/g_glue.c
===================================================================
--- src/lib/gssapi/mechglue/g_glue.c (revision 20093)
+++ src/lib/gssapi/mechglue/g_glue.c (working copy)
@@ -33,6 +33,8 @@
#define MSO_BIT (8*(sizeof (int) - 1)) /* Most significant octet bit */

extern gss_mechanism *gssint_mechs_array;
+#define SPNEGO_OID_LENGTH 6
+#define SPNEGO_OID "\053\006\001\005\005\002"

/*
* This file contains the support routines for the glue layer.
@@ -548,6 +550,8 @@
gss_OID mech_type;
{
int i;
+ gss_union_cred_t spnego_cred;
+ gss_cred_id_t mech_cred;

if (union_cred == GSS_C_NO_CREDENTIAL)
return GSS_C_NO_CREDENTIAL;
@@ -555,6 +559,17 @@
for (i=0; i < union_cred->count; i++) {
if (g_OID_equal(mech_type, &union_cred->mechs_array[i]))
return union_cred->cred_array[i];
+
+ /* if this is an spnego credential, search its contents */
+ if ((union_cred->mechs_array[i].length == SPNEGO_OID_LENGTH) &&
+ (memcmp(union_cred->mechs_array[i].elements,
+ SPNEGO_OID,
+ SPNEGO_OID_LENGTH) == 0)) {
+ spnego_cred = union_cred->cred_array[i];
+ mech_cred = gssint_get_mechanism_cred(spnego_cred, mech_type);
+ if (mech_cred != GSS_C_NO_CREDENTIAL)
+ return mech_cred;
+ }
}
return GSS_C_NO_CREDENTIAL;
}

Apply adapted patch from http://bugs.debian.org/480434 to recurse into
SPNEGO creds when attempting to retrieve a mechanism cred.

Commit By: tlyu



Revision: 20900
Changed Files:
_U trunk/
U trunk/src/lib/gssapi/mechglue/g_glue.c