/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2005 Doug Rabson
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <gssapi/gssapi.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "mech_switch.h"
#include "context.h"
#include "cred.h"
#include "name.h"
#include "utils.h"

static OM_uint32
parse_header(const gss_buffer_t input_token, gss_OID mech_oid)
{
        unsigned char *p = input_token->value;
        size_t len = input_token->length;
        size_t a, b;

        /*
         * Token must start with [APPLICATION 0] SEQUENCE.
         * But if it doesn't assume it is DCE-STYLE Kerberos!
         */
        if (len == 0)
                return (GSS_S_DEFECTIVE_TOKEN);

        p++;
        len--;

        /*
         * Decode the length and make sure it agrees with the
         * token length.
         */
        if (len == 0)
                return (GSS_S_DEFECTIVE_TOKEN);
        if ((*p & 0x80) == 0) {
                a = *p;
                p++;
                len--;
        } else {
                b = *p & 0x7f;
                p++;
                len--;
                if (len < b)
                    return (GSS_S_DEFECTIVE_TOKEN);
                a = 0;
                while (b) {
                    a = (a << 8) | *p;
                    p++;
                    len--;
                    b--;
                }
        }
        if (a != len)
                return (GSS_S_DEFECTIVE_TOKEN);

        /*
         * Decode the OID for the mechanism. Simplify life by
         * assuming that the OID length is less than 128 bytes.
         */
        if (len < 2 || *p != 0x06)
                return (GSS_S_DEFECTIVE_TOKEN);
        if ((p[1] & 0x80) || p[1] > (len - 2))
                return (GSS_S_DEFECTIVE_TOKEN);
        mech_oid->length = p[1];
        p += 2;
        len -= 2;
        mech_oid->elements = p;

        return (GSS_S_COMPLETE);
}

static gss_OID_desc krb5_mechanism =
{9, __DECONST(void *, "\x2a\x86\x48\x86\xf7\x12\x01\x02\x02")};
static gss_OID_desc ntlm_mechanism =
{10, __DECONST(void *, "\x2b\x06\x01\x04\x01\x82\x37\x02\x02\x0a")};
static gss_OID_desc spnego_mechanism =
{6, __DECONST(void *, "\x2b\x06\x01\x05\x05\x02")};

static OM_uint32
choose_mech(const gss_buffer_t input, gss_OID mech_oid)
{
        OM_uint32 status;

        /*
         * First try to parse the gssapi token header and see if it's a
         * correct header, use that in the first hand.
         */

        status = parse_header(input, mech_oid);
        if (status == GSS_S_COMPLETE)
                return (GSS_S_COMPLETE);

        /*
         * Lets guess what mech is really is, callback function to mech ??
         */

        if (input->length > 8 &&
            memcmp((const char *)input->value, "NTLMSSP\x00", 8) == 0)
        {
                *mech_oid = ntlm_mechanism;
                return (GSS_S_COMPLETE);
        } else if (input->length != 0 &&
            ((const char *)input->value)[0] == 0x6E)
        {
                /* Could be a raw AP-REQ (check for APPLICATION tag) */
                *mech_oid = krb5_mechanism;
                return (GSS_S_COMPLETE);
        } else if (input->length == 0) {
                /*
                 * There is the a weird mode of SPNEGO (in CIFS and
                 * SASL GSS-SPENGO where the first token is zero
                 * length and the acceptor returns a mech_list, lets
                 * hope that is what is happening now.
                 */
                *mech_oid = spnego_mechanism;
                return (GSS_S_COMPLETE);
        }
        return (status);
}

OM_uint32 gss_accept_sec_context(OM_uint32 *minor_status,
    gss_ctx_id_t *context_handle,
    const gss_cred_id_t acceptor_cred_handle,
    const gss_buffer_t input_token,
    const gss_channel_bindings_t input_chan_bindings,
    gss_name_t *src_name,
    gss_OID *mech_type,
    gss_buffer_t output_token,
    OM_uint32 *ret_flags,
    OM_uint32 *time_rec,
    gss_cred_id_t *delegated_cred_handle)
{
        OM_uint32 major_status, mech_ret_flags;
        struct _gss_mech_switch *m;
        struct _gss_context *ctx = (struct _gss_context *) *context_handle;
        struct _gss_cred *cred = (struct _gss_cred *) acceptor_cred_handle;
        struct _gss_mechanism_cred *mc;
        gss_cred_id_t acceptor_mc, delegated_mc;
        gss_name_t src_mn;

        *minor_status = 0;
        if (src_name)
                *src_name = GSS_C_NO_NAME;
        if (mech_type)
                *mech_type = GSS_C_NO_OID;
        if (ret_flags)
                *ret_flags = 0;
        if (time_rec)
                *time_rec = 0;
        if (delegated_cred_handle)
                *delegated_cred_handle = GSS_C_NO_CREDENTIAL;
        _gss_buffer_zero(output_token);

        /*
         * If this is the first call (*context_handle is NULL), we must
         * parse the input token to figure out the mechanism to use.
         */
        if (*context_handle == GSS_C_NO_CONTEXT) {
                gss_OID_desc mech_oid;

                major_status = choose_mech(input_token, &mech_oid);
                if (major_status != GSS_S_COMPLETE)
                        return (major_status);

                /*
                 * Now that we have a mechanism, we can find the
                 * implementation.
                 */
                ctx = malloc(sizeof(struct _gss_context));
                if (!ctx) {
                        *minor_status = ENOMEM;
                        return (GSS_S_DEFECTIVE_TOKEN);
                }
                memset(ctx, 0, sizeof(struct _gss_context));
                m = ctx->gc_mech = _gss_find_mech_switch(&mech_oid);
                if (!m) {
                        free(ctx);
                        return (GSS_S_BAD_MECH);
                }
        } else
                m = ctx->gc_mech;

        if (cred) {
                SLIST_FOREACH(mc, &cred->gc_mc, gmc_link)
                        if (mc->gmc_mech == m)
                                break;
                if (!mc)
                        return (GSS_S_BAD_MECH);
                acceptor_mc = mc->gmc_cred;
        } else {
                acceptor_mc = GSS_C_NO_CREDENTIAL;
        }
        delegated_mc = GSS_C_NO_CREDENTIAL;

        mech_ret_flags = 0;
        major_status = m->gm_accept_sec_context(minor_status,
            &ctx->gc_ctx,
            acceptor_mc,
            input_token,
            input_chan_bindings,
            &src_mn,
            mech_type,
            output_token,
            &mech_ret_flags,
            time_rec,
            &delegated_mc);
        if (major_status != GSS_S_COMPLETE &&
            major_status != GSS_S_CONTINUE_NEEDED) {
                _gss_mg_error(m, major_status, *minor_status);
                return (major_status);
        }

        if (src_name && src_mn) {
                /*
                 * Make a new name and mark it as an MN.
                 */
                struct _gss_name *name = _gss_make_name(m, src_mn);

                if (!name) {
                        m->gm_release_name(minor_status, &src_mn);
                        return (GSS_S_FAILURE);
                }
                *src_name = (gss_name_t) name;
        } else if (src_mn) {
                m->gm_release_name(minor_status, &src_mn);
        }

        if (delegated_mc == GSS_C_NO_CREDENTIAL)
                mech_ret_flags &= ~GSS_C_DELEG_FLAG;

        if (mech_ret_flags & GSS_C_DELEG_FLAG) {
                if (!delegated_cred_handle) {
                        m->gm_release_cred(minor_status, &delegated_mc);
                        mech_ret_flags &= ~GSS_C_DELEG_FLAG;
                } else {
                        struct _gss_cred *dcred;
                        struct _gss_mechanism_cred *dmc;

                        dcred = malloc(sizeof(struct _gss_cred));
                        if (!dcred) {
                                *minor_status = ENOMEM;
                                return (GSS_S_FAILURE);
                        }
                        SLIST_INIT(&dcred->gc_mc);
                        dmc = malloc(sizeof(struct _gss_mechanism_cred));
                        if (!dmc) {
                                free(dcred);
                                *minor_status = ENOMEM;
                                return (GSS_S_FAILURE);
                        }
                        dmc->gmc_mech = m;
                        dmc->gmc_mech_oid = &m->gm_mech_oid;
                        dmc->gmc_cred = delegated_mc;
                        SLIST_INSERT_HEAD(&dcred->gc_mc, dmc, gmc_link);

                        *delegated_cred_handle = (gss_cred_id_t) dcred;
                }
        }

        if (ret_flags)
                *ret_flags = mech_ret_flags;
        *context_handle = (gss_ctx_id_t) ctx;
        return (major_status);
}