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Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

/* $OpenBSD: auth-options.c,v 1.45 2010/02/26 20:29:54 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

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

#include <netdb.h>
#include <pwd.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "match.h"
#include "log.h"
#include "canohost.h"
#include "buffer.h"
#include "channels.h"
#include "auth-options.h"
#include "servconf.h"
#include "misc.h"
#include "key.h"
#include "hostfile.h"
#include "auth.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"

/* Flags set authorized_keys flags */
int no_port_forwarding_flag = 0;
int no_agent_forwarding_flag = 0;
int no_x11_forwarding_flag = 0;
int no_pty_flag = 0;
int no_user_rc = 0;
int key_is_cert_authority = 0;

/* "command=" option. */
char *forced_command = NULL;

/* "environment=" options. */
struct envstring *custom_environment = NULL;

/* "tunnel=" option. */
int forced_tun_device = -1;

extern ServerOptions options;

void
auth_clear_options(void)
{
	no_agent_forwarding_flag = 0;
	no_port_forwarding_flag = 0;
	no_pty_flag = 0;
	no_x11_forwarding_flag = 0;
	no_user_rc = 0;
	key_is_cert_authority = 0;
	while (custom_environment) {
		struct envstring *ce = custom_environment;
		custom_environment = ce->next;
		xfree(ce->s);
		xfree(ce);
	}
	if (forced_command) {
		xfree(forced_command);
		forced_command = NULL;
	}
	forced_tun_device = -1;
	channel_clear_permitted_opens();
	auth_debug_reset();
}

/*
 * return 1 if access is granted, 0 if not.
 * side effect: sets key option flags
 */
int
auth_parse_options(struct passwd *pw, char *opts, char *file, u_long linenum)
{
	const char *cp;
	int i;

	/* reset options */
	auth_clear_options();

	if (!opts)
		return 1;

	while (*opts && *opts != ' ' && *opts != '\t') {
		cp = "cert-authority";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			key_is_cert_authority = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "no-port-forwarding";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			auth_debug_add("Port forwarding disabled.");
			no_port_forwarding_flag = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "no-agent-forwarding";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			auth_debug_add("Agent forwarding disabled.");
			no_agent_forwarding_flag = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "no-X11-forwarding";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			auth_debug_add("X11 forwarding disabled.");
			no_x11_forwarding_flag = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "no-pty";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			auth_debug_add("Pty allocation disabled.");
			no_pty_flag = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "no-user-rc";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			auth_debug_add("User rc file execution disabled.");
			no_user_rc = 1;
			opts += strlen(cp);
			goto next_option;
		}
		cp = "command=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			opts += strlen(cp);
			forced_command = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					forced_command[i++] = '"';
					continue;
				}
				forced_command[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				xfree(forced_command);
				forced_command = NULL;
				goto bad_option;
			}
			forced_command[i] = '\0';
			auth_debug_add("Forced command: %.900s", forced_command);
			opts++;
			goto next_option;
		}
		cp = "environment=\"";
		if (options.permit_user_env &&
		    strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *s;
			struct envstring *new_envstring;

			opts += strlen(cp);
			s = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					s[i++] = '"';
					continue;
				}
				s[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				xfree(s);
				goto bad_option;
			}
			s[i] = '\0';
			auth_debug_add("Adding to environment: %.900s", s);
			debug("Adding to environment: %.900s", s);
			opts++;
			new_envstring = xmalloc(sizeof(struct envstring));
			new_envstring->s = s;
			new_envstring->next = custom_environment;
			custom_environment = new_envstring;
			goto next_option;
		}
		cp = "from=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			const char *remote_ip = get_remote_ipaddr();
			const char *remote_host = get_canonical_hostname(
			    options.use_dns);
			char *patterns = xmalloc(strlen(opts) + 1);

			opts += strlen(cp);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					patterns[i++] = '"';
					continue;
				}
				patterns[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				xfree(patterns);
				goto bad_option;
			}
			patterns[i] = '\0';
			opts++;
			switch (match_host_and_ip(remote_host, remote_ip,
			    patterns)) {
			case 1:
				xfree(patterns);
				/* Host name matches. */
				goto next_option;
			case -1:
				debug("%.100s, line %lu: invalid criteria",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: "
				    "invalid criteria", file, linenum);
				/* FALLTHROUGH */
			case 0:
				xfree(patterns);
				logit("Authentication tried for %.100s with "
				    "correct key but not from a permitted "
				    "host (host=%.200s, ip=%.200s).",
				    pw->pw_name, remote_host, remote_ip);
				auth_debug_add("Your host '%.200s' is not "
				    "permitted to use this key for login.",
				    remote_host);
				break;
			}
			/* deny access */
			return 0;
		}
		cp = "permitopen=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *host, *p;
			int port;
			char *patterns = xmalloc(strlen(opts) + 1);

			opts += strlen(cp);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					patterns[i++] = '"';
					continue;
				}
				patterns[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing "
				    "end quote", file, linenum);
				xfree(patterns);
				goto bad_option;
			}
			patterns[i] = '\0';
			opts++;
			p = patterns;
			host = hpdelim(&p);
			if (host == NULL || strlen(host) >= NI_MAXHOST) {
				debug("%.100s, line %lu: Bad permitopen "
				    "specification <%.100s>", file, linenum,
				    patterns);
				auth_debug_add("%.100s, line %lu: "
				    "Bad permitopen specification", file,
				    linenum);
				xfree(patterns);
				goto bad_option;
			}
			host = cleanhostname(host);
			if (p == NULL || (port = a2port(p)) <= 0) {
				debug("%.100s, line %lu: Bad permitopen port "
				    "<%.100s>", file, linenum, p ? p : "");
				auth_debug_add("%.100s, line %lu: "
				    "Bad permitopen port", file, linenum);
				xfree(patterns);
				goto bad_option;
			}
			if (options.allow_tcp_forwarding)
				channel_add_permitted_opens(host, port);
			xfree(patterns);
			goto next_option;
		}
		cp = "tunnel=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *tun = NULL;
			opts += strlen(cp);
			tun = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				tun[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				xfree(tun);
				forced_tun_device = -1;
				goto bad_option;
			}
			tun[i] = '\0';
			forced_tun_device = a2tun(tun, NULL);
			xfree(tun);
			if (forced_tun_device == SSH_TUNID_ERR) {
				debug("%.100s, line %lu: invalid tun device",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: invalid tun device",
				    file, linenum);
				forced_tun_device = -1;
				goto bad_option;
			}
			auth_debug_add("Forced tun device: %d", forced_tun_device);
			opts++;
			goto next_option;
		}
next_option:
		/*
		 * Skip the comma, and move to the next option
		 * (or break out if there are no more).
		 */
		if (!*opts)
			fatal("Bugs in auth-options.c option processing.");
		if (*opts == ' ' || *opts == '\t')
			break;		/* End of options. */
		if (*opts != ',')
			goto bad_option;
		opts++;
		/* Process the next option. */
	}

	if (!use_privsep)
		auth_debug_send();

	/* grant access */
	return 1;

bad_option:
	logit("Bad options in %.100s file, line %lu: %.50s",
	    file, linenum, opts);
	auth_debug_add("Bad options in %.100s file, line %lu: %.50s",
	    file, linenum, opts);

	if (!use_privsep)
		auth_debug_send();

	/* deny access */
	return 0;
}

/*
 * Set options from certificate constraints. These supersede user key options
 * so this must be called after auth_parse_options().
 */
int
auth_cert_constraints(Buffer *c_orig, struct passwd *pw)
{
	u_char *name = NULL, *data_blob = NULL;
	u_int len;
	Buffer c, data;
	int ret = -1;

	int cert_no_port_forwarding_flag = 1;
	int cert_no_agent_forwarding_flag = 1;
	int cert_no_x11_forwarding_flag = 1;
	int cert_no_pty_flag = 1;
	int cert_no_user_rc = 1;
	char *cert_forced_command = NULL;
	int cert_source_address_done = 0;

	buffer_init(&data);

	/* Make copy to avoid altering original */
	buffer_init(&c);
	buffer_append(&c, buffer_ptr(c_orig), buffer_len(c_orig));

	while (buffer_len(&c) > 0) {
		if ((name = buffer_get_string_ret(&c, NULL)) == NULL ||
		    (data_blob = buffer_get_string_ret(&c, &len)) == NULL) {
			error("Certificate constraints corrupt");
			goto out;
		}
		buffer_append(&data, data_blob, len);
		debug3("found certificate constraint \"%.100s\" len %u",
		    name, len);
		if (strcmp(name, "permit-X11-forwarding") == 0)
			cert_no_x11_forwarding_flag = 0;
		else if (strcmp(name, "permit-agent-forwarding") == 0)
			cert_no_agent_forwarding_flag = 0;
		else if (strcmp(name, "permit-port-forwarding") == 0)
			cert_no_port_forwarding_flag = 0;
		else if (strcmp(name, "permit-pty") == 0)
			cert_no_pty_flag = 0;
		else if (strcmp(name, "permit-user-rc") == 0)
			cert_no_user_rc = 0;
		else if (strcmp(name, "force-command") == 0) {
			char *command = buffer_get_string_ret(&data, NULL);

			if (command == NULL) {
				error("Certificate constraint \"%s\" corrupt",
				    name);
				goto out;
			}
			if (cert_forced_command != NULL) {
				error("Certificate has multiple "
				    "forced-command constraints");
				xfree(command);
				goto out;
			}
			cert_forced_command = command;
		} else if (strcmp(name, "source-address") == 0) {
			char *allowed = buffer_get_string_ret(&data, NULL);
			const char *remote_ip = get_remote_ipaddr();
			
			if (allowed == NULL) {
				error("Certificate constraint \"%s\" corrupt",
				    name);
				goto out;
			}
			if (cert_source_address_done++) {
				error("Certificate has multiple "
				    "source-address constraints");
				xfree(allowed);
				goto out;
			}
			switch (addr_match_cidr_list(remote_ip, allowed)) {
			case 1:
				/* accepted */
				xfree(allowed);
				break;
			case 0:
				/* no match */
				logit("Authentication tried for %.100s with "
				    "valid certificate but not from a "
				    "permitted host (ip=%.200s).",
				    pw->pw_name, remote_ip);
				auth_debug_add("Your address '%.200s' is not "
				    "permitted to use this certificate for "
				    "login.", remote_ip);
				xfree(allowed);
				goto out;
			case -1:
				error("Certificate source-address contents "
				    "invalid");
				xfree(allowed);
				goto out;
			}
		} else {
			error("Certificate constraint \"%s\" is not supported",
			    name);
			goto out;
		}

		if (buffer_len(&data) != 0) {
			error("Certificate constraint \"%s\" corrupt "
			    "(extra data)", name);
			goto out;
		}
		buffer_clear(&data);
		xfree(name);
		xfree(data_blob);
		name = data_blob = NULL;
	}

	/* successfully parsed all constraints */
	ret = 0;

	no_port_forwarding_flag |= cert_no_port_forwarding_flag;
	no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
	no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
	no_pty_flag |= cert_no_pty_flag;
	no_user_rc |= cert_no_user_rc;
	/* CA-specified forced command supersedes key option */
	if (cert_forced_command != NULL) {
		if (forced_command != NULL)
			xfree(forced_command);
		forced_command = cert_forced_command;
	}
	
 out:
	if (name != NULL)
		xfree(name);
	if (data_blob != NULL)
		xfree(data_blob);
	buffer_free(&data);
	buffer_free(&c);
	return ret;
}