auth-options.c

/* $OpenBSD: auth-options.c,v 1.49 2010/03/16 15:46:52 stevesk 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 "includes.h"

#include <sys/types.h>

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

#include "openbsd-compat/sys-queue.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();
}

/*
 * 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. */
	}

	/* 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);

	/* 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 nlen, dlen, clen;
	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, &nlen)) == NULL ||
		    (data_blob = buffer_get_string_ret(&c, &dlen)) == NULL) {
			error("Certificate constraints corrupt");
			goto out;
		}
		buffer_append(&data, data_blob, dlen);
		debug3("found certificate constraint \"%.100s\" len %u",
		    name, dlen);
		if (strlen(name) != nlen) {
			error("Certificate constraint name contains \\0");
			goto out;
		}
		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, &clen);

			if (command == NULL) {
				error("Certificate constraint \"%s\" corrupt",
				    name);
				goto out;
			}
			if (strlen(command) != clen) {
				error("force-command constraint contains \\0");
				goto out;
			}
			if (cert_forced_command != NULL) {
				error("Certificate has multiple "
				    "force-command constraints");
				xfree(command);
				goto out;
			}
			cert_forced_command = command;
		} else if (strcmp(name, "source-address") == 0) {
			char *allowed = buffer_get_string_ret(&data, &clen);
			const char *remote_ip = get_remote_ipaddr();
			
			if (allowed == NULL) {
				error("Certificate constraint \"%s\" corrupt",
				    name);
				goto out;
			}
			if (strlen(allowed) != clen) {
				error("source-address constraint contains \\0");
				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;
}