/* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 djm Exp $ */

/*
 * Copyright (c) 2001-2003 Simon Wilkinson. 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 `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 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 "includes.h"

#ifdef GSSAPI

#include <sys/types.h>
#include <sys/param.h>

#include <stdarg.h>
#include <string.h>
#include <unistd.h>

#include "openbsd-compat/sys-queue.h"
#include "xmalloc.h"
#include "sshkey.h"
#include "hostfile.h"
#include "auth.h"
#include "log.h"
#include "channels.h"
#include "session.h"
#include "misc.h"
#include "servconf.h"

#include "ssh-gss.h"

extern ServerOptions options;

static ssh_gssapi_client gssapi_client =
    { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
    GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};

ssh_gssapi_mech gssapi_null_mech =
    { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};

#ifdef KRB5
extern ssh_gssapi_mech gssapi_kerberos_mech;
#endif

ssh_gssapi_mech* supported_mechs[]= {
#ifdef KRB5
        &gssapi_kerberos_mech,
#endif
        &gssapi_null_mech,
};

/*
 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
 * list of supported mechanisms before privsep is set up.
 */
static gss_OID_set supported_oids;

void
ssh_gssapi_prepare_supported_oids(void)
{
        ssh_gssapi_supported_oids(&supported_oids);
}

OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
{
        if (supported_oids == NULL)
                ssh_gssapi_prepare_supported_oids();
        return gss_test_oid_set_member(ms, member, supported_oids, present);
}

/*
 * Acquire credentials for a server running on the current host.
 * Requires that the context structure contains a valid OID
 */

/* Returns a GSSAPI error code */
/* Privileged (called from ssh_gssapi_server_ctx) */
static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt *ctx)
{
        OM_uint32 status;
        char lname[NI_MAXHOST];
        gss_OID_set oidset;

        if (options.gss_strict_acceptor) {
                gss_create_empty_oid_set(&status, &oidset);
                gss_add_oid_set_member(&status, ctx->oid, &oidset);

                if (gethostname(lname, HOST_NAME_MAX)) {
                        gss_release_oid_set(&status, &oidset);
                        return (-1);
                }

                if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
                        gss_release_oid_set(&status, &oidset);
                        return (ctx->major);
                }

                if ((ctx->major = gss_acquire_cred(&ctx->minor,
                    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
                    NULL, NULL)))
                        ssh_gssapi_error(ctx);

                gss_release_oid_set(&status, &oidset);
                return (ctx->major);
        } else {
                ctx->name = GSS_C_NO_NAME;
                ctx->creds = GSS_C_NO_CREDENTIAL;
        }
        return GSS_S_COMPLETE;
}

/* Privileged */
OM_uint32
ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
{
        if (*ctx)
                ssh_gssapi_delete_ctx(ctx);
        ssh_gssapi_build_ctx(ctx);
        ssh_gssapi_set_oid(*ctx, oid);
        return (ssh_gssapi_acquire_cred(*ctx));
}

/* Unprivileged */
void
ssh_gssapi_supported_oids(gss_OID_set *oidset)
{
        int i = 0;
        OM_uint32 min_status;
        int present;
        gss_OID_set supported;

        gss_create_empty_oid_set(&min_status, oidset);
        gss_indicate_mechs(&min_status, &supported);

        while (supported_mechs[i]->name != NULL) {
                if (GSS_ERROR(gss_test_oid_set_member(&min_status,
                    &supported_mechs[i]->oid, supported, &present)))
                        present = 0;
                if (present)
                        gss_add_oid_set_member(&min_status,
                            &supported_mechs[i]->oid, oidset);
                i++;
        }

        gss_release_oid_set(&min_status, &supported);
}


/* Wrapper around accept_sec_context
 * Requires that the context contains:
 *    oid
 *    credentials       (from ssh_gssapi_acquire_cred)
 */
/* Privileged */
OM_uint32
ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
    gss_buffer_desc *send_tok, OM_uint32 *flags)
{
        OM_uint32 status;
        gss_OID mech;

        ctx->major = gss_accept_sec_context(&ctx->minor,
            &ctx->context, ctx->creds, recv_tok,
            GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
            send_tok, flags, NULL, &ctx->client_creds);

        if (GSS_ERROR(ctx->major))
                ssh_gssapi_error(ctx);

        if (ctx->client_creds)
                debug("Received some client credentials");
        else
                debug("Got no client credentials");

        status = ctx->major;

        /* Now, if we're complete and we have the right flags, then
         * we flag the user as also having been authenticated
         */

        if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
            (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
                if (ssh_gssapi_getclient(ctx, &gssapi_client))
                        fatal("Couldn't convert client name");
        }

        return (status);
}

/*
 * This parses an exported name, extracting the mechanism specific portion
 * to use for ACL checking. It verifies that the name belongs the mechanism
 * originally selected.
 */
static OM_uint32
ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
{
        u_char *tok;
        OM_uint32 offset;
        OM_uint32 oidl;

        tok = ename->value;

        /*
         * Check that ename is long enough for all of the fixed length
         * header, and that the initial ID bytes are correct
         */

        if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
                return GSS_S_FAILURE;

        /*
         * Extract the OID, and check it. Here GSSAPI breaks with tradition
         * and does use the OID type and length bytes. To confuse things
         * there are two lengths - the first including these, and the
         * second without.
         */

        oidl = get_u16(tok+2); /* length including next two bytes */
        oidl = oidl-2; /* turn it into the _real_ length of the variable OID */

        /*
         * Check the BER encoding for correct type and length, that the
         * string is long enough and that the OID matches that in our context
         */
        if (tok[4] != 0x06 || tok[5] != oidl ||
            ename->length < oidl+6 ||
            !ssh_gssapi_check_oid(ctx, tok+6, oidl))
                return GSS_S_FAILURE;

        offset = oidl+6;

        if (ename->length < offset+4)
                return GSS_S_FAILURE;

        name->length = get_u32(tok+offset);
        offset += 4;

        if (UINT_MAX - offset < name->length)
                return GSS_S_FAILURE;
        if (ename->length < offset+name->length)
                return GSS_S_FAILURE;

        name->value = xmalloc(name->length+1);
        memcpy(name->value, tok+offset, name->length);
        ((char *)name->value)[name->length] = 0;

        return GSS_S_COMPLETE;
}

/* Extract the client details from a given context. This can only reliably
 * be called once for a context */

/* Privileged (called from accept_secure_ctx) */
OM_uint32
ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
{
        int i = 0;

        gss_buffer_desc ename;

        client->mech = NULL;

        while (supported_mechs[i]->name != NULL) {
                if (supported_mechs[i]->oid.length == ctx->oid->length &&
                    (memcmp(supported_mechs[i]->oid.elements,
                    ctx->oid->elements, ctx->oid->length) == 0))
                        client->mech = supported_mechs[i];
                i++;
        }

        if (client->mech == NULL)
                return GSS_S_FAILURE;

        if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
            &client->displayname, NULL))) {
                ssh_gssapi_error(ctx);
                return (ctx->major);
        }

        if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
            &ename))) {
                ssh_gssapi_error(ctx);
                return (ctx->major);
        }

        if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
            &client->exportedname))) {
                return (ctx->major);
        }

        /* We can't copy this structure, so we just move the pointer to it */
        client->creds = ctx->client_creds;
        ctx->client_creds = GSS_C_NO_CREDENTIAL;
        return (ctx->major);
}

/* As user - called on fatal/exit */
void
ssh_gssapi_cleanup_creds(void)
{
        if (gssapi_client.store.filename != NULL) {
                /* Unlink probably isn't sufficient */
                debug("removing gssapi cred file\"%s\"",
                    gssapi_client.store.filename);
                unlink(gssapi_client.store.filename);
        }
}

/* As user */
void
ssh_gssapi_storecreds(void)
{
        if (gssapi_client.mech && gssapi_client.mech->storecreds) {
                (*gssapi_client.mech->storecreds)(&gssapi_client);
        } else
                debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
}

/* This allows GSSAPI methods to do things to the child's environment based
 * on the passed authentication process and credentials.
 */
/* As user */
void
ssh_gssapi_do_child(char ***envp, u_int *envsizep)
{

        if (gssapi_client.store.envvar != NULL &&
            gssapi_client.store.envval != NULL) {
                debug("Setting %s to %s", gssapi_client.store.envvar,
                    gssapi_client.store.envval);
                child_set_env(envp, envsizep, gssapi_client.store.envvar,
                    gssapi_client.store.envval);
        }
}

/* Privileged */
int
ssh_gssapi_userok(char *user)
{
        OM_uint32 lmin;

        if (gssapi_client.exportedname.length == 0 ||
            gssapi_client.exportedname.value == NULL) {
                debug("No suitable client data");
                return 0;
        }
        if (gssapi_client.mech && gssapi_client.mech->userok)
                if ((*gssapi_client.mech->userok)(&gssapi_client, user))
                        return 1;
                else {
                        /* Destroy delegated credentials if userok fails */
                        gss_release_buffer(&lmin, &gssapi_client.displayname);
                        gss_release_buffer(&lmin, &gssapi_client.exportedname);
                        gss_release_cred(&lmin, &gssapi_client.creds);
                        explicit_bzero(&gssapi_client,
                            sizeof(ssh_gssapi_client));
                        return 0;
                }
        else
                debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
        return (0);
}

/* Privileged */
OM_uint32
ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
{
        ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
            gssbuf, gssmic, NULL);

        return (ctx->major);
}

/* Privileged */
const char *ssh_gssapi_displayname(void)
{
        if (gssapi_client.displayname.length == 0 ||
            gssapi_client.displayname.value == NULL)
                return NULL;
        return (char *)gssapi_client.displayname.value;
}

#endif