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/* $OpenBSD: gss-serv.c,v 1.22 2008/05/08 12:02:23 djm Exp $ */

/*

 * Copyright (c) 2001-2009 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 "buffer.h"

#include "key.h"

#include "hostfile.h"

#include "auth.h"

#include "log.h"

#include "channels.h"

#include "session.h"

#include "misc.h"

#include "servconf.h"

#include "uidswap.h"

#include "ssh-gss.h"

#include "monitor_wrap.h"

extern ServerOptions options;

static ssh_gssapi_client gssapi_client =

    { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,

    GSS_C_NO_CREDENTIAL, GSS_C_NO_NAME,  NULL, {NULL, NULL, NULL}, 0, 0};

ssh_gssapi_mech gssapi_null_mech =

    { NULL, NULL, {0, NULL}, 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,

};

/*

 * 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[MAXHOSTNAMELEN];

	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, MAXHOSTNAMELEN)) {

			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 */

char *

ssh_gssapi_server_mechanisms() {

	gss_OID_set	supported;

	ssh_gssapi_supported_oids(&supported);

	return (ssh_gssapi_kex_mechs(supported, &ssh_gssapi_server_check_mech,

	    NULL, NULL));

}

/* Unprivileged */

int

ssh_gssapi_server_check_mech(Gssctxt **dum, gss_OID oid, const char *data,

    const char *dummy) {

	Gssctxt *ctx = NULL;

	int res;

	res = !GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctx, oid)));

	ssh_gssapi_delete_ctx(&ctx);

	return (res);

}

/* 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);

	if (GSS_ERROR(gss_indicate_mechs(&min_status, &supported)))

		return;

	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 (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;

	int equal = 0;

	gss_name_t new_name = GSS_C_NO_NAME;

	gss_buffer_desc ename = GSS_C_EMPTY_BUFFER;

	if (options.gss_store_rekey && client->used && ctx->client_creds) {

		if (client->mech->oid.length != ctx->oid->length ||

		    (memcmp(client->mech->oid.elements,

		     ctx->oid->elements, ctx->oid->length) !=0)) {

			debug("Rekeyed credentials have different mechanism");

			return GSS_S_COMPLETE;

		}

		if ((ctx->major = gss_inquire_cred_by_mech(&ctx->minor, 

		    ctx->client_creds, ctx->oid, &new_name, 

		    NULL, NULL, NULL))) {

			ssh_gssapi_error(ctx);

			return (ctx->major);

		}

		ctx->major = gss_compare_name(&ctx->minor, client->name, 

		    new_name, &equal);

		if (GSS_ERROR(ctx->major)) {

			ssh_gssapi_error(ctx);

			return (ctx->major);

		}

		if (!equal) {

			debug("Rekeyed credentials have different name");

			return GSS_S_COMPLETE;

		}

		debug("Marking rekeyed credentials for export");

		gss_release_name(&ctx->minor, &client->name);

		gss_release_cred(&ctx->minor, &client->creds);

		client->name = new_name;

		client->creds = ctx->client_creds;

        	ctx->client_creds = GSS_C_NO_CREDENTIAL;

		client->updated = 1;

		return GSS_S_COMPLETE;

	}

	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->client_creds &&

	    (ctx->major = gss_inquire_cred_by_mech(&ctx->minor,

	     ctx->client_creds, ctx->oid, &client->name, NULL, NULL, NULL))) {

		ssh_gssapi_error(ctx);

		return (ctx->major);

	}

	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);

	}

	gss_release_buffer(&ctx->minor, &ename);

	/* 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 childs 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, struct passwd *pw)

{

	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)) {

			gssapi_client.used = 1;

			gssapi_client.store.owner = pw;

			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);

			memset(&gssapi_client, 0, sizeof(ssh_gssapi_client));

			return 0;

		}

	else

		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");

	return (0);

}

/* These bits are only used for rekeying. The unpriviledged child is running 

 * as the user, the monitor is root.

 *

 * In the child, we want to :

 *    *) Ask the monitor to store our credentials into the store we specify

 *    *) If it succeeds, maybe do a PAM update

 */

/* Stuff for PAM */

#ifdef USE_PAM

static int ssh_gssapi_simple_conv(int n, const struct pam_message **msg, 

    struct pam_response **resp, void *data)

{

	return (PAM_CONV_ERR);

}

#endif

void

ssh_gssapi_rekey_creds() {

	int ok;

	int ret;

#ifdef USE_PAM

	pam_handle_t *pamh = NULL;

	struct pam_conv pamconv = {ssh_gssapi_simple_conv, NULL};

	char *envstr;

#endif

	if (gssapi_client.store.filename == NULL && 

	    gssapi_client.store.envval == NULL &&

	    gssapi_client.store.envvar == NULL)

		return;

	ok = PRIVSEP(ssh_gssapi_update_creds(&gssapi_client.store));

	if (!ok)

		return;

	debug("Rekeyed credentials stored successfully");

	/* Actually managing to play with the ssh pam stack from here will

	 * be next to impossible. In any case, we may want different options

	 * for rekeying. So, use our own :)

	 */

#ifdef USE_PAM	

	if (!use_privsep) {

		debug("Not even going to try and do PAM with privsep disabled");

		return;

	}

	ret = pam_start("sshd-rekey", gssapi_client.store.owner->pw_name,

 	    &pamconv, &pamh);

	if (ret)

		return;

	xasprintf(&envstr, "%s=%s", gssapi_client.store.envvar, 

	    gssapi_client.store.envval);

	ret = pam_putenv(pamh, envstr);

	if (!ret)

		pam_setcred(pamh, PAM_REINITIALIZE_CRED);

	pam_end(pamh, PAM_SUCCESS);

#endif

}

int 

ssh_gssapi_update_creds(ssh_gssapi_ccache *store) {

	int ok = 0;

	/* Check we've got credentials to store */

	if (!gssapi_client.updated)

		return 0;

	gssapi_client.updated = 0;

	temporarily_use_uid(gssapi_client.store.owner);

	if (gssapi_client.mech && gssapi_client.mech->updatecreds)

		ok = (*gssapi_client.mech->updatecreds)(store, &gssapi_client);

	else

		debug("No update function for this mechanism");

	restore_uid();

	return ok;

}

#endif