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gss: fix downlevel Windows interop regression

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The recent changes to SPNEGO removed support for GSS_C_PEER_HAS_UPDATED_SPNEGO,
through which the Kerberos mechanism could indicate to SPNEGO that the peer did
not suffer from SPNEGO conformance bugs present in some versions of Windows.*

This patch restores this workaround, documented in [MS-SPNG] Appendix A <7>
Section 3.1.5.1. Whilst improving interoperability with these admittedly now
unsupported versions of Windows, it does introduce a risk that Kerberos with
pre-AES ciphers could be negotiated in lieu of a stronger and more preferred
mechanism.

Note: this patch inverts the mechanism interface from
GSS_C_PEER_HAS_UPDATED_SPNEGO to GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO, so that new
mechanisms (which did not ship with these older versions of Windows) are not
required to implement it.

* Windows 2000, Windows 2003, and Windows XP
This commit is contained in:
Luke Howard
2020-04-09 22:51:30 +10:00
parent 0cb752258e
commit 7df0195c26
7 changed files with 35 additions and 48 deletions
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4
lib/gssapi/gssapi/gssapi_oid.h
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@@ -154,8 +154,8 @@ extern GSSAPI_LIB_VARIABLE gss_OID_desc __gss_spnego_mechanism_oid_desc;
#define GSS_SPNEGO_MECHANISM (&__gss_spnego_mechanism_oid_desc)
/* From Luke Howard */
extern GSSAPI_LIB_VARIABLE gss_OID_desc __gss_c_peer_has_updated_spnego_oid_desc;
#define GSS_C_PEER_HAS_UPDATED_SPNEGO (&__gss_c_peer_has_updated_spnego_oid_desc)
extern GSSAPI_LIB_VARIABLE gss_OID_desc __gss_c_inq_peer_has_buggy_spnego_oid_desc;
#define GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO (&__gss_c_inq_peer_has_buggy_spnego_oid_desc)
extern GSSAPI_LIB_VARIABLE gss_OID_desc __gss_c_ntlm_reset_crypto_oid_desc;
#define GSS_C_NTLM_RESET_CRYPTO (&__gss_c_ntlm_reset_crypto_oid_desc)

40
lib/gssapi/krb5/inquire_sec_context_by_oid.c
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@@ -263,39 +263,31 @@ static OM_uint32 inquire_sec_context_authz_data
return ret;
}
static OM_uint32 inquire_sec_context_has_updated_spnego
static OM_uint32 inquire_sec_context_has_buggy_spnego
(OM_uint32 *minor_status,
const gsskrb5_ctx context_handle,
gss_buffer_set_t *data_set)
{
int is_updated = 0;
uint8_t old_enctype;
gss_buffer_desc buffer;
*minor_status = 0;
*data_set = GSS_C_NO_BUFFER_SET;
/*
* For Windows SPNEGO implementations, both the initiator and the
* acceptor are assumed to have been updated if a "newer" [CLAR] or
* different enctype is negotiated for use by the Kerberos GSS-API
* mechanism.
* For Windows SPNEGO implementations, the initiator or acceptor
* are presumed to be "buggy" (Windows 2003 or earlier) if an
* "older" (i.e. pre-AES per RFC 4121) encryption type was used.
*/
HEIMDAL_MUTEX_lock(&context_handle->ctx_id_mutex);
is_updated = (context_handle->more_flags & IS_CFX);
if (is_updated == 0) {
krb5_keyblock *acceptor_subkey;
if (context_handle->more_flags & LOCAL)
acceptor_subkey = context_handle->auth_context->remote_subkey;
else
acceptor_subkey = context_handle->auth_context->local_subkey;
if (acceptor_subkey != NULL)
is_updated = (acceptor_subkey->keytype !=
context_handle->auth_context->keyblock->keytype);
}
old_enctype = ((context_handle->more_flags & IS_CFX) == 0);
HEIMDAL_MUTEX_unlock(&context_handle->ctx_id_mutex);
return is_updated ? GSS_S_COMPLETE : GSS_S_FAILURE;
buffer.value = &old_enctype;
buffer.length = sizeof(old_enctype);
return gss_add_buffer_set_member(minor_status, &buffer, data_set);
}
/*
@@ -549,10 +541,10 @@ OM_uint32 GSSAPI_CALLCONV _gsskrb5_inquire_sec_context_by_oid
return inquire_sec_context_tkt_flags(minor_status,
ctx,
data_set);
} else if (gss_oid_equal(desired_object, GSS_C_PEER_HAS_UPDATED_SPNEGO)) {
return inquire_sec_context_has_updated_spnego(minor_status,
ctx,
data_set);
} else if (gss_oid_equal(desired_object, GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO)) {
return inquire_sec_context_has_buggy_spnego(minor_status,
ctx,
data_set);
} else if (gss_oid_equal(desired_object, GSS_KRB5_GET_SUBKEY_X)) {
return inquire_sec_context_get_subkey(minor_status,
ctx,

1
lib/gssapi/libgssapi-exports.def
View File

@@ -168,7 +168,6 @@ EXPORTS
__gss_krb5_mechanism_oid_desc DATA
__gss_ntlm_mechanism_oid_desc DATA
__gss_spnego_mechanism_oid_desc DATA
__gss_c_peer_has_updated_spnego_oid_desc DATA
__gss_c_ma_mech_concrete_oid_desc DATA
__gss_c_ma_mech_pseudo_oid_desc DATA
__gss_c_ma_mech_composite_oid_desc DATA

6
lib/gssapi/mech/gss_oid.c
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@@ -142,8 +142,8 @@ gss_OID_desc GSSAPI_LIB_VARIABLE __gss_ntlm_mechanism_oid_desc = { 10, rk_UNCONS
/* GSS_SPNEGO_MECHANISM - 1.3.6.1.5.5.2 */
gss_OID_desc GSSAPI_LIB_VARIABLE __gss_spnego_mechanism_oid_desc = { 6, rk_UNCONST("\x2b\x06\x01\x05\x05\x02") };
/* GSS_C_PEER_HAS_UPDATED_SPNEGO - 1.3.6.1.4.1.5322.19.5 */
gss_OID_desc GSSAPI_LIB_VARIABLE __gss_c_peer_has_updated_spnego_oid_desc = { 9, rk_UNCONST("\x2b\x06\x01\x04\x01\xa9\x4a\x13\x05") };
/* GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO - 1.3.6.1.4.1.5322.19.6 */
gss_OID_desc GSSAPI_LIB_VARIABLE __gss_c_inq_peer_has_buggy_spnego_oid_desc = { 9, rk_UNCONST("\x2b\x06\x01\x04\x01\xa9\x4a\x13\x06") };
/* GSS_C_NTLM_RESET_CRYPTO - 1.3.6.1.4.1.7165.655.1.3 */
gss_OID_desc GSSAPI_LIB_VARIABLE __gss_c_ntlm_reset_crypto_oid_desc = { 11, rk_UNCONST("\x2b\x06\x01\x04\x01\xb7\x7d\x85\x0f\x01\x03") };
@@ -325,7 +325,7 @@ gss_OID _gss_ot_internal[] = {
&__gss_krb5_mechanism_oid_desc,
&__gss_ntlm_mechanism_oid_desc,
&__gss_spnego_mechanism_oid_desc,
&__gss_c_peer_has_updated_spnego_oid_desc,
&__gss_c_inq_peer_has_buggy_spnego_oid_desc,
&__gss_c_ntlm_reset_crypto_oid_desc,
&__gss_negoex_mechanism_oid_desc,
&__gss_c_ma_mech_concrete_oid_desc,

2
lib/gssapi/oid.txt
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@@ -66,7 +66,7 @@ oid base GSS_SPNEGO_MECHANISM 1.3.6.1.5.5.2
# /* From Luke Howard */
oid base GSS_C_PEER_HAS_UPDATED_SPNEGO 1.3.6.1.4.1.5322.19.5
oid base GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO 1.3.6.1.4.1.5322.19.6
oid base GSS_C_NTLM_RESET_CRYPTO 1.3.6.1.4.1.7165.655.1.3
oid base GSS_NEGOEX_MECHANISM 1.3.6.1.4.1.311.2.2.30

29
lib/gssapi/spnego/compat.c
View File

@@ -152,38 +152,30 @@ OM_uint32 GSSAPI_CALLCONV _gss_spnego_internal_delete_sec_context
return ret;
}
/*
* Returns TRUE if the mechanism believes that a mechListMIC is required.
* This is an internal interface for NTLM which requires a mechListMIC if
* an internal MIC in the NTLM protocol was used. Note that only the Samba
* NTLM mechanism supports this, it is not yet implemented in Heimdal's.
*/
static int
mech_require_mechlist_mic_p(gssspnego_ctx ctx)
inq_context_by_oid_bool(gssspnego_ctx ctx, gss_OID oid)
{
OM_uint32 major, minor;
gss_buffer_set_t data_set = GSS_C_NO_BUFFER_SET;
uint8_t mech_require_mic = 0;
uint8_t ret = 0;
major = gss_inquire_sec_context_by_oid(&minor, ctx->negotiated_ctx_id,
GSS_C_INQ_REQUIRE_MECHLIST_MIC, &data_set);
oid, &data_set);
if (major != GSS_S_COMPLETE)
return FALSE;
if (data_set != GSS_C_NO_BUFFER_SET &&
data_set->count == 1 &&
data_set->elements[0].length == 1)
mech_require_mic = *((uint8_t *)data_set->elements[0].value);
ret = *((uint8_t *)data_set->elements[0].value);
gss_release_buffer_set(&minor, &data_set);
return mech_require_mic == 1;
return ret != 0;
}
/*
* Returns TRUE if it is safe to omit mechListMIC because the preferred
* mechanism was selected, and the peer did not require it.
* Returns TRUE if it is safe to omit mechListMIC.
*/
int
@@ -193,11 +185,16 @@ _gss_spnego_safe_omit_mechlist_mic(gssspnego_ctx ctx)
if (ctx->flags.peer_require_mic) {
_gss_mg_log(10, "spnego: mechListMIC required by peer");
} else if (mech_require_mechlist_mic_p(ctx)) {
} else if (inq_context_by_oid_bool(ctx, GSS_C_INQ_PEER_HAS_BUGGY_SPNEGO)) {
/* [MS-SPNG] Appendix A <7> Section 3.1.5.1: may be old peer with buggy SPNEGO */
safe_omit = TRUE;
_gss_mg_log(10, "spnego: mechListMIC omitted for legacy interoperability");
} else if (inq_context_by_oid_bool(ctx, GSS_C_INQ_REQUIRE_MECHLIST_MIC)) {
/* [MS-SPNG] Appendix A <7> Section 3.1.5.1: allow NTLM to force MIC */
_gss_mg_log(10, "spnego: mechListMIC required by mechanism");
} else if (gss_oid_equal(ctx->selected_mech_type, ctx->preferred_mech_type)) {
safe_omit = TRUE;
_gss_mg_log(10, "spnego: mechListMIC may be omitted as preferred mechanism selected");
_gss_mg_log(10, "spnego: mechListMIC omitted as preferred mechanism selected");
} else {
_gss_mg_log(10, "spnego: mechListMIC required by default");
}

1
lib/gssapi/version-script.map
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@@ -171,7 +171,6 @@ HEIMDAL_GSS_2.0 {
__gss_krb5_mechanism_oid_desc;
__gss_ntlm_mechanism_oid_desc;
__gss_spnego_mechanism_oid_desc;
__gss_c_peer_has_updated_spnego_oid_desc;
__gss_c_ma_mech_concrete_oid_desc;
__gss_c_ma_mech_pseudo_oid_desc;
__gss_c_ma_mech_composite_oid_desc;