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gss: allow partial accept context export in SPNEGO

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Support for exporting partially established acceptor context tokens. With this,
an acceptor can send the initiator an encrypted state cookie containing the
exported context token.

(The concrete mechanism, of course, must either require a single round trip or
support partial context export itself. Kerberos and GSS EAP would work, but
Kerberos with GSS_C_DCE_STYLE would not, as currently implemented.)

Partial context export is not permitted for initiators.
This commit is contained in:
Luke Howard
2021-08-05 07:57:40 +10:00
parent fe426f7a28
commit 6554dc69b0
7 changed files with 695 additions and 105 deletions
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74
lib/gssapi/spnego/negoex_ctx.c
View File

@@ -1,5 +1,5 @@
/*
* Copyright (C) 2011-2019 PADL Software Pty Ltd.
* Copyright (C) 2011-2021 PADL Software Pty Ltd.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@@ -88,33 +88,42 @@ buffer_set_to_crypto(OM_uint32 *minor,
return GSS_S_COMPLETE;
}
#define NEGOEX_SIGN_KEY 1
#define NEGOEX_VERIFY_KEY 2
#define NEGOEX_BOTH_KEYS (NEGOEX_SIGN_KEY|NEGOEX_VERIFY_KEY)
static OM_uint32
get_session_keys(OM_uint32 *minor,
krb5_context context,
OM_uint32 flags,
struct negoex_auth_mech *mech)
{
OM_uint32 major, tmpMinor;
gss_buffer_set_t buffers = GSS_C_NO_BUFFER_SET;
major = gss_inquire_sec_context_by_oid(&tmpMinor, mech->mech_context,
GSS_C_INQ_NEGOEX_KEY, &buffers);
if (major == GSS_S_COMPLETE) {
major = buffer_set_to_crypto(minor, context,
buffers, &mech->crypto);
_gss_secure_release_buffer_set(&tmpMinor, &buffers);
if (major != GSS_S_COMPLETE)
return major;
if (flags & NEGOEX_SIGN_KEY) {
major = gss_inquire_sec_context_by_oid(&tmpMinor, mech->mech_context,
GSS_C_INQ_NEGOEX_KEY, &buffers);
if (major == GSS_S_COMPLETE) {
major = buffer_set_to_crypto(minor, context,
buffers, &mech->crypto);
_gss_secure_release_buffer_set(&tmpMinor, &buffers);
if (major != GSS_S_COMPLETE)
return major;
}
}
major = gss_inquire_sec_context_by_oid(&tmpMinor, mech->mech_context,
GSS_C_INQ_NEGOEX_VERIFY_KEY,
&buffers);
if (major == GSS_S_COMPLETE) {
major = buffer_set_to_crypto(minor, context,
buffers, &mech->verify_crypto);
_gss_secure_release_buffer_set(&tmpMinor, &buffers);
if (major != GSS_S_COMPLETE)
return major;
if (flags & NEGOEX_VERIFY_KEY) {
major = gss_inquire_sec_context_by_oid(&tmpMinor, mech->mech_context,
GSS_C_INQ_NEGOEX_VERIFY_KEY,
&buffers);
if (major == GSS_S_COMPLETE) {
major = buffer_set_to_crypto(minor, context,
buffers, &mech->verify_crypto);
_gss_secure_release_buffer_set(&tmpMinor, &buffers);
if (major != GSS_S_COMPLETE)
return major;
}
}
return GSS_S_COMPLETE;
@@ -411,7 +420,7 @@ mech_init(OM_uint32 *minor,
}
}
if (!GSS_ERROR(major))
return get_session_keys(minor, context, mech);
return get_session_keys(minor, context, NEGOEX_BOTH_KEYS, mech);
/* Remember the error we got from the first mech. */
if (first_mech) {
@@ -509,7 +518,7 @@ mech_accept(OM_uint32 *minor,
!gss_oid_equal(ctx->negotiated_mech_type, mech->oid))
_gss_mg_log(1, "negoex client didn't send the mech they said they would");
major = get_session_keys(minor, context, mech);
major = get_session_keys(minor, context, NEGOEX_BOTH_KEYS, mech);
} else if (ctx->negoex_step == 1) {
gss_mg_collect_error(ctx->negotiated_mech_type, major, *minor);
*mech_error = TRUE;
@@ -532,6 +541,13 @@ verify_keyusage(gssspnego_ctx ctx, int make_checksum)
NEGOEX_KEYUSAGE_ACCEPTOR_CHECKSUM : NEGOEX_KEYUSAGE_INITIATOR_CHECKSUM;
}
static OM_uint32
verify_key_flags(gssspnego_ctx ctx, int make_checksum)
{
return (ctx->flags.local ^ make_checksum) ?
NEGOEX_SIGN_KEY : NEGOEX_VERIFY_KEY;
}
static OM_uint32
verify_checksum(OM_uint32 *minor,
gssspnego_ctx ctx,
@@ -558,6 +574,13 @@ verify_checksum(OM_uint32 *minor,
if (msg == NULL || !GUID_EQ(msg->scheme, mech->scheme))
return GSS_S_COMPLETE;
/*
* Last chance attempt to obtain session key for imported exported partial
* contexts (which do not carry the session key at the NegoEx layer).
*/
if (mech->verify_crypto == NULL)
get_session_keys(minor, context, verify_key_flags(ctx, FALSE), mech);
/*
* A recoverable error may cause us to be unable to verify a token from the
* other party. In this case we should send an alert.
@@ -618,8 +641,15 @@ make_checksum(OM_uint32 *minor, gssspnego_ctx ctx)
if (mech->crypto == NULL) {
if (mech->complete) {
*minor = (OM_uint32)NEGOEX_NO_VERIFY_KEY;
return GSS_S_UNAVAILABLE;
/*
* Last chance attempt to obtain session key for imported exported partial
* contexts (which do not carry the session key at the NegoEx layer).
*/
get_session_keys(minor, context, verify_key_flags(ctx, TRUE), mech);
if (mech->crypto == NULL) {
*minor = (OM_uint32)NEGOEX_NO_VERIFY_KEY;
return GSS_S_UNAVAILABLE;
}
} else {
return GSS_S_COMPLETE;
}