auth2-pubkey.c - security/openssh-library - Rivoreo Source Code Repositories

 /* $OpenBSD: auth2-pubkey.c,v 1.49 2015/05/04 06:10:48 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  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"

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>

 #include <errno.h>
 #include <fcntl.h>
 #ifdef HAVE_PATHS_H
 # include <paths.h>
 #endif
 #include <pwd.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
 #include <limits.h>

 #include "xmalloc.h"
 #include "ssh.h"
 #include "ssh2.h"
 #include "packet.h"
 #include "buffer.h"
 #include "log.h"
 #include "misc.h"
 #include "servconf.h"
 #include "compat.h"
 #include "key.h"
 #include "hostfile.h"
 #include "auth.h"
 #include "pathnames.h"
 #include "uidswap.h"
 #include "auth-options.h"
 #include "canohost.h"
 #ifdef GSSAPI
 #include "ssh-gss.h"
 #endif
 #include "monitor_wrap.h"
 #include "authfile.h"
 #include "match.h"

 /* import */
 extern ServerOptions options;
 extern u_char *session_id2;
 extern u_int session_id2_len;

 static int
 userauth_pubkey(Authctxt *authctxt)
 {
 	Buffer b;
 	Key *key = NULL;
 	char *pkalg, *userstyle;
 	u_char *pkblob, *sig;
 	u_int alen, blen, slen;
 	int have_sig, pktype;
 	int authenticated = 0;

 	if (!authctxt->valid) {
 		debug2("userauth_pubkey: disabled because of invalid user");
 		return 0;
 	}
 	have_sig = packet_get_char();
 	if (datafellows & SSH_BUG_PKAUTH) {
 		debug2("userauth_pubkey: SSH_BUG_PKAUTH");
 		/* no explicit pkalg given */
 		pkblob = packet_get_string(&blen);
 		buffer_init(&b);
 		buffer_append(&b, pkblob, blen);
 		/* so we have to extract the pkalg from the pkblob */
 		pkalg = buffer_get_string(&b, &alen);
 		buffer_free(&b);
 	} else {
 		pkalg = packet_get_string(&alen);
 		pkblob = packet_get_string(&blen);
 	}
 	pktype = key_type_from_name(pkalg);
 	if (pktype == KEY_UNSPEC) {
 		/* this is perfectly legal */
 		logit("userauth_pubkey: unsupported public key algorithm: %s",
 		    pkalg);
 		goto done;
 	}
 	key = key_from_blob(pkblob, blen);
 	if (key == NULL) {
 		error("userauth_pubkey: cannot decode key: %s", pkalg);
 		goto done;
 	}
 	if (key->type != pktype) {
 		error("userauth_pubkey: type mismatch for decoded key "
 		    "(received %d, expected %d)", key->type, pktype);
 		goto done;
 	}
 	if (key_type_plain(key->type) == KEY_RSA &&
 	    (datafellows & SSH_BUG_RSASIGMD5) != 0) {
 		logit("Refusing RSA key because client uses unsafe "
 		    "signature scheme");
 		goto done;
 	}
 	if (auth2_userkey_already_used(authctxt, key)) {
 		logit("refusing previously-used %s key", key_type(key));
 		goto done;
 	}
 	if (match_pattern_list(sshkey_ssh_name(key),
 	    options.pubkey_key_types, 0) != 1) {
 		logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
 		    __func__, sshkey_ssh_name(key));
 		goto done;
 	}

 	if (have_sig) {
 		sig = packet_get_string(&slen);
 		packet_check_eom();
 		buffer_init(&b);
 		if (datafellows & SSH_OLD_SESSIONID) {
 			buffer_append(&b, session_id2, session_id2_len);
 		} else {
 			buffer_put_string(&b, session_id2, session_id2_len);
 		}
 		/* reconstruct packet */
 		buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 		xasprintf(&userstyle, "%s%s%s", authctxt->user,
 		    authctxt->style ? ":" : "",
 		    authctxt->style ? authctxt->style : "");
 		buffer_put_cstring(&b, userstyle);
 		free(userstyle);
 		buffer_put_cstring(&b,
 		    datafellows & SSH_BUG_PKSERVICE ?
 		    "ssh-userauth" :
 		    authctxt->service);
 		if (datafellows & SSH_BUG_PKAUTH) {
 			buffer_put_char(&b, have_sig);
 		} else {
 			buffer_put_cstring(&b, "publickey");
 			buffer_put_char(&b, have_sig);
 			buffer_put_cstring(&b, pkalg);
 		}
 		buffer_put_string(&b, pkblob, blen);
 #ifdef DEBUG_PK
 		buffer_dump(&b);
 #endif
 		pubkey_auth_info(authctxt, key, NULL);

 		/* test for correct signature */
 		authenticated = 0;
 		if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 		    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 		    buffer_len(&b))) == 1) {
 			authenticated = 1;
 			/* Record the successful key to prevent reuse */
 			auth2_record_userkey(authctxt, key);
 			key = NULL; /* Don't free below */
 		}
 		buffer_free(&b);
 		free(sig);
 	} else {
 		debug("test whether pkalg/pkblob are acceptable");
 		packet_check_eom();

 		/* XXX fake reply and always send PK_OK ? */
 		/*
 		 * XXX this allows testing whether a user is allowed
 		 * to login: if you happen to have a valid pubkey this
 		 * message is sent. the message is NEVER sent at all
 		 * if a user is not allowed to login. is this an
 		 * issue? -markus
 		 */
 		if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 			packet_start(SSH2_MSG_USERAUTH_PK_OK);
 			packet_put_string(pkalg, alen);
 			packet_put_string(pkblob, blen);
 			packet_send();
 			packet_write_wait();
 			authctxt->postponed = 1;
 		}
 	}
 	if (authenticated != 1)
 		auth_clear_options();
 done:
 	debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 	if (key != NULL)
 		key_free(key);
 	free(pkalg);
 	free(pkblob);
 	return authenticated;
 }

 void
 pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...)
 {
 	char *fp, *extra;
 	va_list ap;
 	int i;

 	extra = NULL;
 	if (fmt != NULL) {
 		va_start(ap, fmt);
 		i = vasprintf(&extra, fmt, ap);
 		va_end(ap);
 		if (i < 0 || extra == NULL)
 			fatal("%s: vasprintf failed", __func__);
 	}

 	if (key_is_cert(key)) {
 		fp = sshkey_fingerprint(key->cert->signature_key,
 		    options.fingerprint_hash, SSH_FP_DEFAULT);
 		auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
 		    key_type(key), key->cert->key_id,
 		    (unsigned long long)key->cert->serial,
 		    key_type(key->cert->signature_key),
 		    fp == NULL ? "(null)" : fp,
 		    extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
 		free(fp);
 	} else {
 		fp = sshkey_fingerprint(key, options.fingerprint_hash,
 		    SSH_FP_DEFAULT);
 		auth_info(authctxt, "%s %s%s%s", key_type(key),
 		    fp == NULL ? "(null)" : fp,
 		    extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
 		free(fp);
 	}
 	free(extra);
 }

 static int
 match_principals_option(const char *principal_list, struct sshkey_cert *cert)
 {
 	char *result;
 	u_int i;

 	/* XXX percent_expand() sequences for authorized_principals? */

 	for (i = 0; i < cert->nprincipals; i++) {
 		if ((result = match_list(cert->principals[i],
 		    principal_list, NULL)) != NULL) {
 			debug3("matched principal from key options \"%.100s\"",
 			    result);
 			free(result);
 			return 1;
 		}
 	}
 	return 0;
 }

 static int
 match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
 {
 	FILE *f;
 	char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 	u_long linenum = 0;
 	u_int i;

 	temporarily_use_uid(pw);
 	debug("trying authorized principals file %s", file);
 	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
 		restore_uid();
 		return 0;
 	}
 	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 		/* Skip leading whitespace. */
 		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 			;
 		/* Skip blank and comment lines. */
 		if ((ep = strchr(cp, '#')) != NULL)
 			*ep = '\0';
 		if (!*cp || *cp == '\n')
 			continue;
 		/* Trim trailing whitespace. */
 		ep = cp + strlen(cp) - 1;
 		while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
 			*ep-- = '\0';
 		/*
 		 * If the line has internal whitespace then assume it has
 		 * key options.
 		 */
 		line_opts = NULL;
 		if ((ep = strrchr(cp, ' ')) != NULL ||
 		    (ep = strrchr(cp, '\t')) != NULL) {
 			for (; *ep == ' ' || *ep == '\t'; ep++)
 				;
 			line_opts = cp;
 			cp = ep;
 		}
 		for (i = 0; i < cert->nprincipals; i++) {
 			if (strcmp(cp, cert->principals[i]) == 0) {
 				debug3("matched principal \"%.100s\" "
 				    "from file \"%s\" on line %lu",
 				    cert->principals[i], file, linenum);
 				if (auth_parse_options(pw, line_opts,
 				    file, linenum) != 1)
 					continue;
 				fclose(f);
 				restore_uid();
 				return 1;
 			}
 		}
 	}
 	fclose(f);
 	restore_uid();
 	return 0;
 }

 /*
  * Checks whether key is allowed in authorized_keys-format file,
  * returns 1 if the key is allowed or 0 otherwise.
  */
 static int
 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
 {
 	char line[SSH_MAX_PUBKEY_BYTES];
 	const char *reason;
 	int found_key = 0;
 	u_long linenum = 0;
 	Key *found;
 	char *fp;

 	found_key = 0;

 	found = NULL;
 	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 		char *cp, *key_options = NULL;
 		if (found != NULL)
 			key_free(found);
 		found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 		auth_clear_options();

 		/* Skip leading whitespace, empty and comment lines. */
 		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 			;
 		if (!*cp || *cp == '\n' || *cp == '#')
 			continue;

 		if (key_read(found, &cp) != 1) {
 			/* no key?  check if there are options for this key */
 			int quoted = 0;
 			debug2("user_key_allowed: check options: '%s'", cp);
 			key_options = cp;
 			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 				if (*cp == '\\' && cp[1] == '"')
 					cp++;	/* Skip both */
 				else if (*cp == '"')
 					quoted = !quoted;
 			}
 			/* Skip remaining whitespace. */
 			for (; *cp == ' ' || *cp == '\t'; cp++)
 				;
 			if (key_read(found, &cp) != 1) {
 				debug2("user_key_allowed: advance: '%s'", cp);
 				/* still no key?  advance to next line*/
 				continue;
 			}
 		}
 		if (key_is_cert(key)) {
 			if (!key_equal(found, key->cert->signature_key))
 				continue;
 			if (auth_parse_options(pw, key_options, file,
 			    linenum) != 1)
 				continue;
 			if (!key_is_cert_authority)
 				continue;
 			if ((fp = sshkey_fingerprint(found,
 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 				continue;
 			debug("matching CA found: file %s, line %lu, %s %s",
 			    file, linenum, key_type(found), fp);
 			/*
 			 * If the user has specified a list of principals as
 			 * a key option, then prefer that list to matching
 			 * their username in the certificate principals list.
 			 */
 			if (authorized_principals != NULL &&
 			    !match_principals_option(authorized_principals,
 			    key->cert)) {
 				reason = "Certificate does not contain an "
 				    "authorized principal";
  fail_reason:
 				free(fp);
 				error("%s", reason);
 				auth_debug_add("%s", reason);
 				continue;
 			}
 			if (key_cert_check_authority(key, 0, 0,
 			    authorized_principals == NULL ? pw->pw_name : NULL,
 			    &reason) != 0)
 				goto fail_reason;
 			if (auth_cert_options(key, pw) != 0) {
 				free(fp);
 				continue;
 			}
 			verbose("Accepted certificate ID \"%s\" "
 			    "signed by %s CA %s via %s", key->cert->key_id,
 			    key_type(found), fp, file);
 			free(fp);
 			found_key = 1;
 			break;
 		} else if (key_equal(found, key)) {
 			if (auth_parse_options(pw, key_options, file,
 			    linenum) != 1)
 				continue;
 			if (key_is_cert_authority)
 				continue;
 			if ((fp = sshkey_fingerprint(found,
 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 				continue;
 			debug("matching key found: file %s, line %lu %s %s",
 			    file, linenum, key_type(found), fp);
 			free(fp);
 			found_key = 1;
 			break;
 		}
 	}
 	if (found != NULL)
 		key_free(found);
 	if (!found_key)
 		debug2("key not found");
 	return found_key;
 }

 /* Authenticate a certificate key against TrustedUserCAKeys */
 static int
 user_cert_trusted_ca(struct passwd *pw, Key *key)
 {
 	char *ca_fp, *principals_file = NULL;
 	const char *reason;
 	int ret = 0;

 	if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 		return 0;

 	if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
 	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 		return 0;

 	if (sshkey_in_file(key->cert->signature_key,
 	    options.trusted_user_ca_keys, 1, 0) != 0) {
 		debug2("%s: CA %s %s is not listed in %s", __func__,
 		    key_type(key->cert->signature_key), ca_fp,
 		    options.trusted_user_ca_keys);
 		goto out;
 	}
 	/*
 	 * If AuthorizedPrincipals is in use, then compare the certificate
 	 * principals against the names in that file rather than matching
 	 * against the username.
 	 */
 	if ((principals_file = authorized_principals_file(pw)) != NULL) {
 		if (!match_principals_file(principals_file, pw, key->cert)) {
 			reason = "Certificate does not contain an "
 			    "authorized principal";
  fail_reason:
 			error("%s", reason);
 			auth_debug_add("%s", reason);
 			goto out;
 		}
 	}
 	if (key_cert_check_authority(key, 0, 1,
 	    principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
 		goto fail_reason;
 	if (auth_cert_options(key, pw) != 0)
 		goto out;

 	verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
 	    key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
 	    options.trusted_user_ca_keys);
 	ret = 1;

  out:
 	free(principals_file);
 	free(ca_fp);
 	return ret;
 }

 /*
  * Checks whether key is allowed in file.
  * returns 1 if the key is allowed or 0 otherwise.
  */
 static int
 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 {
 	FILE *f;
 	int found_key = 0;

 	/* Temporarily use the user's uid. */
 	temporarily_use_uid(pw);

 	debug("trying public key file %s", file);
 	if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
 		found_key = check_authkeys_file(f, file, key, pw);
 		fclose(f);
 	}

 	restore_uid();
 	return found_key;
 }

 /*
  * Checks whether key is allowed in output of command.
  * returns 1 if the key is allowed or 0 otherwise.
  */
 static int
 user_key_command_allowed2(struct passwd *user_pw, Key *key)
 {
 	FILE *f;
 	int ok, found_key = 0;
 	struct passwd *pw;
 	struct stat st;
 	int status, devnull, p[2], i;
 	pid_t pid;
 	char *username, errmsg[512];

 	if (options.authorized_keys_command == NULL ||
 	    options.authorized_keys_command[0] != '/')
 		return 0;

 	if (options.authorized_keys_command_user == NULL) {
 		error("No user for AuthorizedKeysCommand specified, skipping");
 		return 0;
 	}

 	username = percent_expand(options.authorized_keys_command_user,
 	    "u", user_pw->pw_name, (char *)NULL);
 	pw = getpwnam(username);
 	if (pw == NULL) {
 		error("AuthorizedKeysCommandUser \"%s\" not found: %s",
 		    username, strerror(errno));
 		free(username);
 		return 0;
 	}
 	free(username);

 	temporarily_use_uid(pw);

 	if (stat(options.authorized_keys_command, &st) < 0) {
 		error("Could not stat AuthorizedKeysCommand \"%s\": %s",
 		    options.authorized_keys_command, strerror(errno));
 		goto out;
 	}
 	if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
 	    errmsg, sizeof(errmsg)) != 0) {
 		error("Unsafe AuthorizedKeysCommand: %s", errmsg);
 		goto out;
 	}

 	if (pipe(p) != 0) {
 		error("%s: pipe: %s", __func__, strerror(errno));
 		goto out;
 	}

 	debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
 	    options.authorized_keys_command, user_pw->pw_name, pw->pw_name);

 	/*
 	 * Don't want to call this in the child, where it can fatal() and
 	 * run cleanup_exit() code.
 	 */
 	restore_uid();

 	switch ((pid = fork())) {
 	case -1: /* error */
 		error("%s: fork: %s", __func__, strerror(errno));
 		close(p[0]);
 		close(p[1]);
 		return 0;
 	case 0: /* child */
 		for (i = 0; i < NSIG; i++)
 			signal(i, SIG_DFL);

 		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
 			error("%s: open %s: %s", __func__, _PATH_DEVNULL,
 			    strerror(errno));
 			_exit(1);
 		}
 		/* Keep stderr around a while longer to catch errors */
 		if (dup2(devnull, STDIN_FILENO) == -1 ||
 		    dup2(p[1], STDOUT_FILENO) == -1) {
 			error("%s: dup2: %s", __func__, strerror(errno));
 			_exit(1);
 		}
 		closefrom(STDERR_FILENO + 1);

 		/* Don't use permanently_set_uid() here to avoid fatal() */
 		if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
 			error("setresgid %u: %s", (u_int)pw->pw_gid,
 			    strerror(errno));
 			_exit(1);
 		}
 		if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
 			error("setresuid %u: %s", (u_int)pw->pw_uid,
 			    strerror(errno));
 			_exit(1);
 		}
 		/* stdin is pointed to /dev/null at this point */
 		if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
 			error("%s: dup2: %s", __func__, strerror(errno));
 			_exit(1);
 		}

 		execl(options.authorized_keys_command,
 		    options.authorized_keys_command, user_pw->pw_name, NULL);

 		error("AuthorizedKeysCommand %s exec failed: %s",
 		    options.authorized_keys_command, strerror(errno));
 		_exit(127);
 	default: /* parent */
 		break;
 	}

 	temporarily_use_uid(pw);

 	close(p[1]);
 	if ((f = fdopen(p[0], "r")) == NULL) {
 		error("%s: fdopen: %s", __func__, strerror(errno));
 		close(p[0]);
 		/* Don't leave zombie child */
 		kill(pid, SIGTERM);
 		while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
 			;
 		goto out;
 	}
 	ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
 	fclose(f);

 	while (waitpid(pid, &status, 0) == -1) {
 		if (errno != EINTR) {
 			error("%s: waitpid: %s", __func__, strerror(errno));
 			goto out;
 		}
 	}
 	if (WIFSIGNALED(status)) {
 		error("AuthorizedKeysCommand %s exited on signal %d",
 		    options.authorized_keys_command, WTERMSIG(status));
 		goto out;
 	} else if (WEXITSTATUS(status) != 0) {
 		error("AuthorizedKeysCommand %s returned status %d",
 		    options.authorized_keys_command, WEXITSTATUS(status));
 		goto out;
 	}
 	found_key = ok;
  out:
 	restore_uid();
 	return found_key;
 }

 /*
  * Check whether key authenticates and authorises the user.
  */
 int
 user_key_allowed(struct passwd *pw, Key *key)
 {
 	u_int success, i;
 	char *file;

 	if (auth_key_is_revoked(key))
 		return 0;
 	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
 		return 0;

 	success = user_cert_trusted_ca(pw, key);
 	if (success)
 		return success;

 	success = user_key_command_allowed2(pw, key);
 	if (success > 0)
 		return success;

 	for (i = 0; !success && i < options.num_authkeys_files; i++) {

 		if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
 			continue;
 		file = expand_authorized_keys(
 		    options.authorized_keys_files[i], pw);

 		success = user_key_allowed2(pw, key, file);
 		free(file);
 	}

 	return success;
 }

 /* Records a public key in the list of previously-successful keys */
 void
 auth2_record_userkey(Authctxt *authctxt, struct sshkey *key)
 {
 	struct sshkey **tmp;

 	if (authctxt->nprev_userkeys >= INT_MAX ||
 	    (tmp = reallocarray(authctxt->prev_userkeys,
 	    authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL)
 		fatal("%s: reallocarray failed", __func__);
 	authctxt->prev_userkeys = tmp;
 	authctxt->prev_userkeys[authctxt->nprev_userkeys] = key;
 	authctxt->nprev_userkeys++;
 }

 /* Checks whether a key has already been used successfully for authentication */
 int
 auth2_userkey_already_used(Authctxt *authctxt, struct sshkey *key)
 {
 	u_int i;

 	for (i = 0; i < authctxt->nprev_userkeys; i++) {
 		if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) {
 			return 1;
 		}
 	}
 	return 0;
 }

 Authmethod method_pubkey = {
 	"publickey",
 	userauth_pubkey,
 	&options.pubkey_authentication
 };
	/* $OpenBSD: auth2-pubkey.c,v 1.49 2015/05/04 06:10:48 djm Exp $ */
	/*
	* Copyright (c) 2000 Markus Friedl. 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"

	#include <sys/types.h>
	#include <sys/stat.h>
	#include <sys/wait.h>

	#include <errno.h>
	#include <fcntl.h>
	#ifdef HAVE_PATHS_H
	# include <paths.h>
	#endif
	#include <pwd.h>
	#include <signal.h>
	#include <stdio.h>
	#include <stdarg.h>
	#include <string.h>
	#include <time.h>
	#include <unistd.h>
	#include <limits.h>

	#include "xmalloc.h"
	#include "ssh.h"
	#include "ssh2.h"
	#include "packet.h"
	#include "buffer.h"
	#include "log.h"
	#include "misc.h"
	#include "servconf.h"
	#include "compat.h"
	#include "key.h"
	#include "hostfile.h"
	#include "auth.h"
	#include "pathnames.h"
	#include "uidswap.h"
	#include "auth-options.h"
	#include "canohost.h"
	#ifdef GSSAPI
	#include "ssh-gss.h"
	#endif
	#include "monitor_wrap.h"
	#include "authfile.h"
	#include "match.h"

	/* import */
	extern ServerOptions options;
	extern u_char *session_id2;
	extern u_int session_id2_len;

	static int
	userauth_pubkey(Authctxt *authctxt)
	{
	Buffer b;
	Key *key = NULL;
	char pkalg, userstyle;
	u_char pkblob, sig;
	u_int alen, blen, slen;
	int have_sig, pktype;
	int authenticated = 0;

	if (!authctxt->valid) {
	debug2("userauth_pubkey: disabled because of invalid user");
	return 0;
	}
	have_sig = packet_get_char();
	if (datafellows & SSH_BUG_PKAUTH) {
	debug2("userauth_pubkey: SSH_BUG_PKAUTH");
	/* no explicit pkalg given */
	pkblob = packet_get_string(&blen);
	buffer_init(&b);
	buffer_append(&b, pkblob, blen);
	/* so we have to extract the pkalg from the pkblob */
	pkalg = buffer_get_string(&b, &alen);
	buffer_free(&b);
	} else {
	pkalg = packet_get_string(&alen);
	pkblob = packet_get_string(&blen);
	}
	pktype = key_type_from_name(pkalg);
	if (pktype == KEY_UNSPEC) {
	/* this is perfectly legal */
	logit("userauth_pubkey: unsupported public key algorithm: %s",
	pkalg);
	goto done;
	}
	key = key_from_blob(pkblob, blen);
	if (key == NULL) {
	error("userauth_pubkey: cannot decode key: %s", pkalg);
	goto done;
	}
	if (key->type != pktype) {
	error("userauth_pubkey: type mismatch for decoded key "
	"(received %d, expected %d)", key->type, pktype);
	goto done;
	}
	if (key_type_plain(key->type) == KEY_RSA &&
	(datafellows & SSH_BUG_RSASIGMD5) != 0) {
	logit("Refusing RSA key because client uses unsafe "
	"signature scheme");
	goto done;
	}
	if (auth2_userkey_already_used(authctxt, key)) {
	logit("refusing previously-used %s key", key_type(key));
	goto done;
	}
	if (match_pattern_list(sshkey_ssh_name(key),
	options.pubkey_key_types, 0) != 1) {
	logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
	__func__, sshkey_ssh_name(key));
	goto done;
	}

	if (have_sig) {
	sig = packet_get_string(&slen);
	packet_check_eom();
	buffer_init(&b);
	if (datafellows & SSH_OLD_SESSIONID) {
	buffer_append(&b, session_id2, session_id2_len);
	} else {
	buffer_put_string(&b, session_id2, session_id2_len);
	}
	/* reconstruct packet */
	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
	xasprintf(&userstyle, "%s%s%s", authctxt->user,
	authctxt->style ? ":" : "",
	authctxt->style ? authctxt->style : "");
	buffer_put_cstring(&b, userstyle);
	free(userstyle);
	buffer_put_cstring(&b,
	datafellows & SSH_BUG_PKSERVICE ?
	"ssh-userauth" :
	authctxt->service);
	if (datafellows & SSH_BUG_PKAUTH) {
	buffer_put_char(&b, have_sig);
	} else {
	buffer_put_cstring(&b, "publickey");
	buffer_put_char(&b, have_sig);
	buffer_put_cstring(&b, pkalg);
	}
	buffer_put_string(&b, pkblob, blen);
	#ifdef DEBUG_PK
	buffer_dump(&b);
	#endif
	pubkey_auth_info(authctxt, key, NULL);

	/* test for correct signature */
	authenticated = 0;
	if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
	PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
	buffer_len(&b))) == 1) {
	authenticated = 1;
	/* Record the successful key to prevent reuse */
	auth2_record_userkey(authctxt, key);
	key = NULL; /* Don't free below */
	}
	buffer_free(&b);
	free(sig);
	} else {
	debug("test whether pkalg/pkblob are acceptable");
	packet_check_eom();

	/* XXX fake reply and always send PK_OK ? */
	/*
	* XXX this allows testing whether a user is allowed
	* to login: if you happen to have a valid pubkey this
	* message is sent. the message is NEVER sent at all
	* if a user is not allowed to login. is this an
	* issue? -markus
	*/
	if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
	packet_start(SSH2_MSG_USERAUTH_PK_OK);
	packet_put_string(pkalg, alen);
	packet_put_string(pkblob, blen);
	packet_send();
	packet_write_wait();
	authctxt->postponed = 1;
	}
	}
	if (authenticated != 1)
	auth_clear_options();
	done:
	debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
	if (key != NULL)
	key_free(key);
	free(pkalg);
	free(pkblob);
	return authenticated;
	}

	void
	pubkey_auth_info(Authctxt authctxt, const Key key, const char *fmt, ...)
	{
	char fp, extra;
	va_list ap;
	int i;

	extra = NULL;
	if (fmt != NULL) {
	va_start(ap, fmt);
	i = vasprintf(&extra, fmt, ap);
	va_end(ap);
	if (i < 0 \|\| extra == NULL)
	fatal("%s: vasprintf failed", __func__);
	}

	if (key_is_cert(key)) {
	fp = sshkey_fingerprint(key->cert->signature_key,
	options.fingerprint_hash, SSH_FP_DEFAULT);
	auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
	key_type(key), key->cert->key_id,
	(unsigned long long)key->cert->serial,
	key_type(key->cert->signature_key),
	fp == NULL ? "(null)" : fp,
	extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
	free(fp);
	} else {
	fp = sshkey_fingerprint(key, options.fingerprint_hash,
	SSH_FP_DEFAULT);
	auth_info(authctxt, "%s %s%s%s", key_type(key),
	fp == NULL ? "(null)" : fp,
	extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
	free(fp);
	}
	free(extra);
	}

	static int
	match_principals_option(const char principal_list, struct sshkey_cert cert)
	{
	char *result;
	u_int i;

	/* XXX percent_expand() sequences for authorized_principals? */

	for (i = 0; i < cert->nprincipals; i++) {
	if ((result = match_list(cert->principals[i],
	principal_list, NULL)) != NULL) {
	debug3("matched principal from key options \"%.100s\"",
	result);
	free(result);
	return 1;
	}
	}
	return 0;
	}

	static int
	match_principals_file(char file, struct passwd pw, struct sshkey_cert *cert)
	{
	FILE *f;
	char line[SSH_MAX_PUBKEY_BYTES], cp, ep, *line_opts;
	u_long linenum = 0;
	u_int i;

	temporarily_use_uid(pw);
	debug("trying authorized principals file %s", file);
	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
	restore_uid();
	return 0;
	}
	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
	/* Skip leading whitespace. */
	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	;
	/* Skip blank and comment lines. */
	if ((ep = strchr(cp, '#')) != NULL)
	*ep = '\0';
	if (!cp \|\| cp == '\n')
	continue;
	/* Trim trailing whitespace. */
	ep = cp + strlen(cp) - 1;
	while (ep > cp && (ep == '\n' \|\| ep == ' ' \|\| *ep == '\t'))
	*ep-- = '\0';
	/*
	* If the line has internal whitespace then assume it has
	* key options.
	*/
	line_opts = NULL;
	if ((ep = strrchr(cp, ' ')) != NULL \|\|
	(ep = strrchr(cp, '\t')) != NULL) {
	for (; ep == ' ' \|\| ep == '\t'; ep++)
	;
	line_opts = cp;
	cp = ep;
	}
	for (i = 0; i < cert->nprincipals; i++) {
	if (strcmp(cp, cert->principals[i]) == 0) {
	debug3("matched principal \"%.100s\" "
	"from file \"%s\" on line %lu",
	cert->principals[i], file, linenum);
	if (auth_parse_options(pw, line_opts,
	file, linenum) != 1)
	continue;
	fclose(f);
	restore_uid();
	return 1;
	}
	}
	}
	fclose(f);
	restore_uid();
	return 0;
	}

	/*
	* Checks whether key is allowed in authorized_keys-format file,
	* returns 1 if the key is allowed or 0 otherwise.
	*/
	static int
	check_authkeys_file(FILE f, char file, Key* key, struct passwd *pw)
	{
	char line[SSH_MAX_PUBKEY_BYTES];
	const char *reason;
	int found_key = 0;
	u_long linenum = 0;
	Key *found;
	char *fp;

	found_key = 0;

	found = NULL;
	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
	char cp, key_options = NULL;
	if (found != NULL)
	key_free(found);
	found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
	auth_clear_options();

	/* Skip leading whitespace, empty and comment lines. */
	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	;
	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	continue;

	if (key_read(found, &cp) != 1) {
	/* no key? check if there are options for this key */
	int quoted = 0;
	debug2("user_key_allowed: check options: '%s'", cp);
	key_options = cp;
	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	if (*cp == '\\' && cp[1] == '"')
	cp++; /* Skip both */
	else if (*cp == '"')
	quoted = !quoted;
	}
	/* Skip remaining whitespace. */
	for (; cp == ' ' \|\| cp == '\t'; cp++)
	;
	if (key_read(found, &cp) != 1) {
	debug2("user_key_allowed: advance: '%s'", cp);
	/* still no key? advance to next line*/
	continue;
	}
	}
	if (key_is_cert(key)) {
	if (!key_equal(found, key->cert->signature_key))
	continue;
	if (auth_parse_options(pw, key_options, file,
	linenum) != 1)
	continue;
	if (!key_is_cert_authority)
	continue;
	if ((fp = sshkey_fingerprint(found,
	options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
	continue;
	debug("matching CA found: file %s, line %lu, %s %s",
	file, linenum, key_type(found), fp);
	/*
	* If the user has specified a list of principals as
	* a key option, then prefer that list to matching
	* their username in the certificate principals list.
	*/
	if (authorized_principals != NULL &&
	!match_principals_option(authorized_principals,
	key->cert)) {
	reason = "Certificate does not contain an "
	"authorized principal";
	fail_reason:
	free(fp);
	error("%s", reason);
	auth_debug_add("%s", reason);
	continue;
	}
	if (key_cert_check_authority(key, 0, 0,
	authorized_principals == NULL ? pw->pw_name : NULL,
	&reason) != 0)
	goto fail_reason;
	if (auth_cert_options(key, pw) != 0) {
	free(fp);
	continue;
	}
	verbose("Accepted certificate ID \"%s\" "
	"signed by %s CA %s via %s", key->cert->key_id,
	key_type(found), fp, file);
	free(fp);
	found_key = 1;
	break;
	} else if (key_equal(found, key)) {
	if (auth_parse_options(pw, key_options, file,
	linenum) != 1)
	continue;
	if (key_is_cert_authority)
	continue;
	if ((fp = sshkey_fingerprint(found,
	options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
	continue;
	debug("matching key found: file %s, line %lu %s %s",
	file, linenum, key_type(found), fp);
	free(fp);
	found_key = 1;
	break;
	}
	}
	if (found != NULL)
	key_free(found);
	if (!found_key)
	debug2("key not found");
	return found_key;
	}

	/* Authenticate a certificate key against TrustedUserCAKeys */
	static int
	user_cert_trusted_ca(struct passwd pw, Key key)
	{
	char ca_fp, principals_file = NULL;
	const char *reason;
	int ret = 0;

	if (!key_is_cert(key) \|\| options.trusted_user_ca_keys == NULL)
	return 0;

	if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
	options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
	return 0;

	if (sshkey_in_file(key->cert->signature_key,
	options.trusted_user_ca_keys, 1, 0) != 0) {
	debug2("%s: CA %s %s is not listed in %s", __func__,
	key_type(key->cert->signature_key), ca_fp,
	options.trusted_user_ca_keys);
	goto out;
	}
	/*
	* If AuthorizedPrincipals is in use, then compare the certificate
	* principals against the names in that file rather than matching
	* against the username.
	*/
	if ((principals_file = authorized_principals_file(pw)) != NULL) {
	if (!match_principals_file(principals_file, pw, key->cert)) {
	reason = "Certificate does not contain an "
	"authorized principal";
	fail_reason:
	error("%s", reason);
	auth_debug_add("%s", reason);
	goto out;
	}
	}
	if (key_cert_check_authority(key, 0, 1,
	principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
	goto fail_reason;
	if (auth_cert_options(key, pw) != 0)
	goto out;

	verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
	key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
	options.trusted_user_ca_keys);
	ret = 1;

	out:
	free(principals_file);
	free(ca_fp);
	return ret;
	}

	/*
	* Checks whether key is allowed in file.
	* returns 1 if the key is allowed or 0 otherwise.
	*/
	static int
	user_key_allowed2(struct passwd pw, Key key, char *file)
	{
	FILE *f;
	int found_key = 0;

	/* Temporarily use the user's uid. */
	temporarily_use_uid(pw);

	debug("trying public key file %s", file);
	if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
	found_key = check_authkeys_file(f, file, key, pw);
	fclose(f);
	}

	restore_uid();
	return found_key;
	}

	/*
	* Checks whether key is allowed in output of command.
	* returns 1 if the key is allowed or 0 otherwise.
	*/
	static int
	user_key_command_allowed2(struct passwd user_pw, Key key)
	{
	FILE *f;
	int ok, found_key = 0;
	struct passwd *pw;
	struct stat st;
	int status, devnull, p[2], i;
	pid_t pid;
	char *username, errmsg[512];

	if (options.authorized_keys_command == NULL \|\|
	options.authorized_keys_command[0] != '/')
	return 0;

	if (options.authorized_keys_command_user == NULL) {
	error("No user for AuthorizedKeysCommand specified, skipping");
	return 0;
	}

	username = percent_expand(options.authorized_keys_command_user,
	"u", user_pw->pw_name, (char *)NULL);
	pw = getpwnam(username);
	if (pw == NULL) {
	error("AuthorizedKeysCommandUser \"%s\" not found: %s",
	username, strerror(errno));
	free(username);
	return 0;
	}
	free(username);

	temporarily_use_uid(pw);

	if (stat(options.authorized_keys_command, &st) < 0) {
	error("Could not stat AuthorizedKeysCommand \"%s\": %s",
	options.authorized_keys_command, strerror(errno));
	goto out;
	}
	if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
	errmsg, sizeof(errmsg)) != 0) {
	error("Unsafe AuthorizedKeysCommand: %s", errmsg);
	goto out;
	}

	if (pipe(p) != 0) {
	error("%s: pipe: %s", __func__, strerror(errno));
	goto out;
	}

	debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
	options.authorized_keys_command, user_pw->pw_name, pw->pw_name);

	/*
	* Don't want to call this in the child, where it can fatal() and
	* run cleanup_exit() code.
	*/
	restore_uid();

	switch ((pid = fork())) {
	case -1: /* error */
	error("%s: fork: %s", __func__, strerror(errno));
	close(p[0]);
	close(p[1]);
	return 0;
	case 0: /* child */
	for (i = 0; i < NSIG; i++)
	signal(i, SIG_DFL);

	if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
	error("%s: open %s: %s", __func__, _PATH_DEVNULL,
	strerror(errno));
	_exit(1);
	}
	/* Keep stderr around a while longer to catch errors */
	if (dup2(devnull, STDIN_FILENO) == -1 \|\|
	dup2(p[1], STDOUT_FILENO) == -1) {
	error("%s: dup2: %s", __func__, strerror(errno));
	_exit(1);
	}
	closefrom(STDERR_FILENO + 1);

	/* Don't use permanently_set_uid() here to avoid fatal() */
	if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
	error("setresgid %u: %s", (u_int)pw->pw_gid,
	strerror(errno));
	_exit(1);
	}
	if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
	error("setresuid %u: %s", (u_int)pw->pw_uid,
	strerror(errno));
	_exit(1);
	}
	/* stdin is pointed to /dev/null at this point */
	if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
	error("%s: dup2: %s", __func__, strerror(errno));
	_exit(1);
	}

	execl(options.authorized_keys_command,
	options.authorized_keys_command, user_pw->pw_name, NULL);

	error("AuthorizedKeysCommand %s exec failed: %s",
	options.authorized_keys_command, strerror(errno));
	_exit(127);
	default: /* parent */
	break;
	}

	temporarily_use_uid(pw);

	close(p[1]);
	if ((f = fdopen(p[0], "r")) == NULL) {
	error("%s: fdopen: %s", __func__, strerror(errno));
	close(p[0]);
	/* Don't leave zombie child */
	kill(pid, SIGTERM);
	while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
	;
	goto out;
	}
	ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
	fclose(f);

	while (waitpid(pid, &status, 0) == -1) {
	if (errno != EINTR) {
	error("%s: waitpid: %s", __func__, strerror(errno));
	goto out;
	}
	}
	if (WIFSIGNALED(status)) {
	error("AuthorizedKeysCommand %s exited on signal %d",
	options.authorized_keys_command, WTERMSIG(status));
	goto out;
	} else if (WEXITSTATUS(status) != 0) {
	error("AuthorizedKeysCommand %s returned status %d",
	options.authorized_keys_command, WEXITSTATUS(status));
	goto out;
	}
	found_key = ok;
	out:
	restore_uid();
	return found_key;
	}

	/*
	* Check whether key authenticates and authorises the user.
	*/
	int
	user_key_allowed(struct passwd pw, Key key)
	{
	u_int success, i;
	char *file;

	if (auth_key_is_revoked(key))
	return 0;
	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
	return 0;

	success = user_cert_trusted_ca(pw, key);
	if (success)
	return success;

	success = user_key_command_allowed2(pw, key);
	if (success > 0)
	return success;

	for (i = 0; !success && i < options.num_authkeys_files; i++) {

	if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
	continue;
	file = expand_authorized_keys(
	options.authorized_keys_files[i], pw);

	success = user_key_allowed2(pw, key, file);
	free(file);
	}

	return success;
	}

	/* Records a public key in the list of previously-successful keys */
	void
	auth2_record_userkey(Authctxt authctxt, struct sshkey key)
	{
	struct sshkey **tmp;

	if (authctxt->nprev_userkeys >= INT_MAX \|\|
	(tmp = reallocarray(authctxt->prev_userkeys,
	authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL)
	fatal("%s: reallocarray failed", __func__);
	authctxt->prev_userkeys = tmp;
	authctxt->prev_userkeys[authctxt->nprev_userkeys] = key;
	authctxt->nprev_userkeys++;
	}

	/* Checks whether a key has already been used successfully for authentication */
	int
	auth2_userkey_already_used(Authctxt authctxt, struct sshkey key)
	{
	u_int i;

	for (i = 0; i < authctxt->nprev_userkeys; i++) {
	if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) {
	return 1;
	}
	}
	return 0;
	}

	Authmethod method_pubkey = {
	"publickey",
	userauth_pubkey,
	&options.pubkey_authentication
	};