svr-authpubkey.c - third_party/dropbear - Git at Google

 /*
  * Dropbear - a SSH2 server
  *
  * Copyright (c) 2002,2003 Matt Johnston
  * All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE. */
 /*
  * This file incorporates work covered by the following copyright and
  * permission notice:
  *
  * 	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.
  *
  * This copyright and permission notice applies to the code parsing public keys
  * options string which can also be found in OpenSSH auth2-pubkey.c file
  * (user_key_allowed2). It has been adapted to work with buffers.
  *
  */

 /* Process a pubkey auth request */

 #include "includes.h"
 #include "session.h"
 #include "dbutil.h"
 #include "buffer.h"
 #include "signkey.h"
 #include "auth.h"
 #include "ssh.h"
 #include "packet.h"
 #include "algo.h"

 #ifdef ENABLE_SVR_PUBKEY_AUTH

 #define MIN_AUTHKEYS_LINE 10 /* "ssh-rsa AB" - short but doesn't matter */
 #define MAX_AUTHKEYS_LINE 4200 /* max length of a line in authkeys */

 static int checkpubkey(unsigned char* algo, unsigned int algolen,
 		unsigned char* keyblob, unsigned int keybloblen);
 static int checkpubkeyperms();
 static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
 		unsigned char* keyblob, unsigned int keybloblen);
 static int checkfileperm(char * filename);

 /* process a pubkey auth request, sending success or failure message as
  * appropriate */
 void svr_auth_pubkey() {

 	unsigned char testkey; /* whether we're just checking if a key is usable */
 	unsigned char* algo = NULL; /* pubkey algo */
 	unsigned int algolen;
 	unsigned char* keyblob = NULL;
 	unsigned int keybloblen;
 	buffer * signbuf = NULL;
 	sign_key * key = NULL;
 	char* fp = NULL;
 	int type = -1;

 	TRACE(("enter pubkeyauth"))

 	/* 0 indicates user just wants to check if key can be used, 1 is an
 	 * actual attempt*/
 	testkey = (buf_getbool(ses.payload) == 0);

 	algo = buf_getstring(ses.payload, &algolen);
 	keybloblen = buf_getint(ses.payload);
 	keyblob = buf_getptr(ses.payload, keybloblen);

 	/* check if the key is valid */
 	if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
 		send_msg_userauth_failure(0, 0);
 		goto out;
 	}

 	/* let them know that the key is ok to use */
 	if (testkey) {
 		send_msg_userauth_pk_ok(algo, algolen, keyblob, keybloblen);
 		goto out;
 	}

 	/* now we can actually verify the signature */

 	/* get the key */
 	key = new_sign_key();
 	type = DROPBEAR_SIGNKEY_ANY;
 	if (buf_get_pub_key(ses.payload, key, &type) == DROPBEAR_FAILURE) {
 		send_msg_userauth_failure(0, 1);
 		goto out;
 	}

 	/* create the data which has been signed - this a string containing
 	 * session_id, concatenated with the payload packet up to the signature */
 	signbuf = buf_new(ses.payload->pos + 4 + SHA1_HASH_SIZE);
 	buf_putstring(signbuf, ses.session_id, SHA1_HASH_SIZE);
 	buf_putbytes(signbuf, ses.payload->data, ses.payload->pos);
 	buf_setpos(signbuf, 0);

 	/* ... and finally verify the signature */
 	fp = sign_key_fingerprint(keyblob, keybloblen);
 	if (buf_verify(ses.payload, key, buf_getptr(signbuf, signbuf->len),
 				signbuf->len) == DROPBEAR_SUCCESS) {
 		dropbear_log(LOG_NOTICE,
 				"Pubkey auth succeeded for '%s' with key %s from %s",
 				ses.authstate.pw_name, fp, svr_ses.addrstring);
 		send_msg_userauth_success();
 	} else {
 		dropbear_log(LOG_WARNING,
 				"Pubkey auth bad signature for '%s' with key %s from %s",
 				ses.authstate.pw_name, fp, svr_ses.addrstring);
 		send_msg_userauth_failure(0, 1);
 	}
 	m_free(fp);

 out:
 	/* cleanup stuff */
 	if (signbuf) {
 		buf_free(signbuf);
 	}
 	if (algo) {
 		m_free(algo);
 	}
 	if (key) {
 		sign_key_free(key);
 		key = NULL;
 	}
 	TRACE(("leave pubkeyauth"))
 }

 /* Reply that the key is valid for auth, this is sent when the user sends
  * a straight copy of their pubkey to test, to avoid having to perform
  * expensive signing operations with a worthless key */
 static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
 		unsigned char* keyblob, unsigned int keybloblen) {

 	TRACE(("enter send_msg_userauth_pk_ok"))
 	CHECKCLEARTOWRITE();

 	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_PK_OK);
 	buf_putstring(ses.writepayload, algo, algolen);
 	buf_putstring(ses.writepayload, keyblob, keybloblen);

 	encrypt_packet();
 	TRACE(("leave send_msg_userauth_pk_ok"))

 }

 /* Checks whether a specified publickey (and associated algorithm) is an
  * acceptable key for authentication */
 /* Returns DROPBEAR_SUCCESS if key is ok for auth, DROPBEAR_FAILURE otherwise */
 static int checkpubkey(unsigned char* algo, unsigned int algolen,
 		unsigned char* keyblob, unsigned int keybloblen) {

 	FILE * authfile = NULL;
 	char * filename = NULL;
 	int ret = DROPBEAR_FAILURE;
 	buffer * line = NULL;
 	unsigned int len, pos;
 	buffer * options_buf = NULL;
 	int line_num;

 	TRACE(("enter checkpubkey"))

 	/* check that we can use the algo */
 	if (have_algo(algo, algolen, sshhostkey) == DROPBEAR_FAILURE) {
 		dropbear_log(LOG_WARNING,
 				"Pubkey auth attempt with unknown algo for '%s' from %s",
 				ses.authstate.pw_name, svr_ses.addrstring);
 		goto out;
 	}

 	/* check file permissions, also whether file exists */
 	if (checkpubkeyperms() == DROPBEAR_FAILURE) {
 		TRACE(("bad authorized_keys permissions, or file doesn't exist"))
 		goto out;
 	}

 	/* we don't need to check pw and pw_dir for validity, since
 	 * its been done in checkpubkeyperms. */
 	len = strlen(ses.authstate.pw_dir);
 	/* allocate max required pathname storage,
 	 * = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
 	filename = m_malloc(len + 22);
 	snprintf(filename, len + 22, "%s/.ssh/authorized_keys",
 				ses.authstate.pw_dir);

 	/* open the file */
 	authfile = fopen(filename, "r");
 	if (authfile == NULL) {
 		goto out;
 	}
 	TRACE(("checkpubkey: opened authorized_keys OK"))

 	line = buf_new(MAX_AUTHKEYS_LINE);
 	line_num = 0;

 	/* iterate through the lines */
 	do {
 		/* new line : potentially new options */
 		if (options_buf) {
 			buf_free(options_buf);
 			options_buf = NULL;
 		}

 		if (buf_getline(line, authfile) == DROPBEAR_FAILURE) {
 			/* EOF reached */
 			TRACE(("checkpubkey: authorized_keys EOF reached"))
 			break;
 		}
 		line_num++;

 		if (line->len < MIN_AUTHKEYS_LINE) {
 			TRACE(("checkpubkey: line too short"))
 			continue; /* line is too short for it to be a valid key */
 		}

 		/* check the key type - will fail if there are options */
 		TRACE(("a line!"))

 		if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
 			int is_comment = 0;
 			char *options_start = NULL;
 			int options_len = 0;
 			int escape, quoted;

 			/* skip over any comments or leading whitespace */
 			while (line->pos < line->len) {
 				const char c = buf_getbyte(line);
 				if (c == ' ' || c == '\t') {
 					continue;
 				} else if (c == '#') {
 					is_comment = 1;
 					break;
 				}
 				buf_incrpos(line, -1);
 				break;
 			}
 			if (is_comment) {
 				/* next line */
 				continue;
 			}

 			/* remember start of options */
 			options_start = buf_getptr(line, 1);
 			quoted = 0;
 			escape = 0;
 			options_len = 0;

 			/* figure out where the options are */
 			while (line->pos < line->len) {
 				const char c = buf_getbyte(line);
 				if (!quoted && (c == ' ' || c == '\t')) {
 					break;
 				}
 				escape = (!escape && c == '\\');
 				if (!escape && c == '"') {
 					quoted = !quoted;
 				}
 				options_len++;
 			}
 			options_buf = buf_new(options_len);
 			buf_putbytes(options_buf, options_start, options_len);

 			/* compare the algorithm */
 			if (line->pos + algolen > line->len) {
 				continue;
 			}
 			if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
 				continue;
 			}
 		}
 		buf_incrpos(line, algolen);

 		/* check for space (' ') character */
 		if (buf_getbyte(line) != ' ') {
 			TRACE(("checkpubkey: space character expected, isn't there"))
 			continue;
 		}

 		/* truncate the line at the space after the base64 data */
 		pos = line->pos;
 		for (len = 0; line->pos < line->len; len++) {
 			if (buf_getbyte(line) == ' ') break;
 		}
 		buf_setpos(line, pos);
 		buf_setlen(line, line->pos + len);

 		TRACE(("checkpubkey: line pos = %d len = %d", line->pos, line->len))

 		ret = cmp_base64_key(keyblob, keybloblen, algo, algolen, line, NULL);

 		if (ret == DROPBEAR_SUCCESS && options_buf) {
 			ret = svr_add_pubkey_options(options_buf, line_num, filename);
 		}

 		if (ret == DROPBEAR_SUCCESS) {
 			break;
 		}

 		/* We continue to the next line otherwise */

 	} while (1);

 out:
 	if (authfile) {
 		fclose(authfile);
 	}
 	if (line) {
 		buf_free(line);
 	}
 	m_free(filename);
 	if (options_buf) {
 		buf_free(options_buf);
 	}
 	TRACE(("leave checkpubkey: ret=%d", ret))
 	return ret;
 }


 /* Returns DROPBEAR_SUCCESS if file permissions for pubkeys are ok,
  * DROPBEAR_FAILURE otherwise.
  * Checks that the user's homedir, ~/.ssh, and
  * ~/.ssh/authorized_keys are all owned by either root or the user, and are
  * g-w, o-w */
 static int checkpubkeyperms() {

 	char* filename = NULL;
 	int ret = DROPBEAR_FAILURE;
 	unsigned int len;

 	TRACE(("enter checkpubkeyperms"))

 	if (ses.authstate.pw_dir == NULL) {
 		goto out;
 	}

 	if ((len = strlen(ses.authstate.pw_dir)) == 0) {
 		goto out;
 	}

 	/* allocate max required pathname storage,
 	 * = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
 	filename = m_malloc(len + 22);
 	strncpy(filename, ses.authstate.pw_dir, len+1);

 	/* check ~ */
 	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
 		goto out;
 	}

 	/* check ~/.ssh */
 	strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */
 	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
 		goto out;
 	}

 	/* now check ~/.ssh/authorized_keys */
 	strncat(filename, "/authorized_keys", 16);
 	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
 		goto out;
 	}

 	/* file looks ok, return success */
 	ret = DROPBEAR_SUCCESS;

 out:
 	m_free(filename);

 	TRACE(("leave checkpubkeyperms"))
 	return ret;
 }

 /* Checks that a file is owned by the user or root, and isn't writable by
  * group or other */
 /* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
 static int checkfileperm(char * filename) {
 	struct stat filestat;
 	int badperm = 0;

 	TRACE(("enter checkfileperm(%s)", filename))

 	if (stat(filename, &filestat) != 0) {
 		TRACE(("leave checkfileperm: stat() != 0"))
 		return DROPBEAR_FAILURE;
 	}
 	/* check ownership - user or root only*/
 	if (filestat.st_uid != ses.authstate.pw_uid
 			&& filestat.st_uid != 0) {
 		badperm = 1;
 		TRACE(("wrong ownership"))
 	}
 	/* check permissions - don't want group or others +w */
 	if (filestat.st_mode & (S_IWGRP | S_IWOTH)) {
 		badperm = 1;
 		TRACE(("wrong perms"))
 	}
 	if (badperm) {
 		if (!ses.authstate.perm_warn) {
 			ses.authstate.perm_warn = 1;
 			dropbear_log(LOG_INFO, "%s must be owned by user or root, and not writable by others", filename);
 		}
 		TRACE(("leave checkfileperm: failure perms/owner"))
 		return DROPBEAR_FAILURE;
 	}

 	TRACE(("leave checkfileperm: success"))
 	return DROPBEAR_SUCCESS;
 }

 #endif
	/*
	* Dropbear - a SSH2 server
	*
	* Copyright (c) 2002,2003 Matt Johnston
	* All rights reserved.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE. */
	/*
	* This file incorporates work covered by the following copyright and
	* permission notice:
	*
	* 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.
	*
	* This copyright and permission notice applies to the code parsing public keys
	* options string which can also be found in OpenSSH auth2-pubkey.c file
	* (user_key_allowed2). It has been adapted to work with buffers.
	*
	*/

	/* Process a pubkey auth request */

	#include "includes.h"
	#include "session.h"
	#include "dbutil.h"
	#include "buffer.h"
	#include "signkey.h"
	#include "auth.h"
	#include "ssh.h"
	#include "packet.h"
	#include "algo.h"

	#ifdef ENABLE_SVR_PUBKEY_AUTH

	#define MIN_AUTHKEYS_LINE 10 /* "ssh-rsa AB" - short but doesn't matter */
	#define MAX_AUTHKEYS_LINE 4200 /* max length of a line in authkeys */

	static int checkpubkey(unsigned char* algo, unsigned int algolen,
	unsigned char* keyblob, unsigned int keybloblen);
	static int checkpubkeyperms();
	static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
	unsigned char* keyblob, unsigned int keybloblen);
	static int checkfileperm(char * filename);

	/* process a pubkey auth request, sending success or failure message as
	* appropriate */
	void svr_auth_pubkey() {

	unsigned char testkey; /* whether we're just checking if a key is usable */
	unsigned char* algo = NULL; /* pubkey algo */
	unsigned int algolen;
	unsigned char* keyblob = NULL;
	unsigned int keybloblen;
	buffer * signbuf = NULL;
	sign_key * key = NULL;
	char* fp = NULL;
	int type = -1;

	TRACE(("enter pubkeyauth"))

	/* 0 indicates user just wants to check if key can be used, 1 is an
	* actual attempt*/
	testkey = (buf_getbool(ses.payload) == 0);

	algo = buf_getstring(ses.payload, &algolen);
	keybloblen = buf_getint(ses.payload);
	keyblob = buf_getptr(ses.payload, keybloblen);

	/* check if the key is valid */
	if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
	send_msg_userauth_failure(0, 0);
	goto out;
	}

	/* let them know that the key is ok to use */
	if (testkey) {
	send_msg_userauth_pk_ok(algo, algolen, keyblob, keybloblen);
	goto out;
	}

	/* now we can actually verify the signature */

	/* get the key */
	key = new_sign_key();
	type = DROPBEAR_SIGNKEY_ANY;
	if (buf_get_pub_key(ses.payload, key, &type) == DROPBEAR_FAILURE) {
	send_msg_userauth_failure(0, 1);
	goto out;
	}

	/* create the data which has been signed - this a string containing
	* session_id, concatenated with the payload packet up to the signature */
	signbuf = buf_new(ses.payload->pos + 4 + SHA1_HASH_SIZE);
	buf_putstring(signbuf, ses.session_id, SHA1_HASH_SIZE);
	buf_putbytes(signbuf, ses.payload->data, ses.payload->pos);
	buf_setpos(signbuf, 0);

	/* ... and finally verify the signature */
	fp = sign_key_fingerprint(keyblob, keybloblen);
	if (buf_verify(ses.payload, key, buf_getptr(signbuf, signbuf->len),
	signbuf->len) == DROPBEAR_SUCCESS) {
	dropbear_log(LOG_NOTICE,
	"Pubkey auth succeeded for '%s' with key %s from %s",
	ses.authstate.pw_name, fp, svr_ses.addrstring);
	send_msg_userauth_success();
	} else {
	dropbear_log(LOG_WARNING,
	"Pubkey auth bad signature for '%s' with key %s from %s",
	ses.authstate.pw_name, fp, svr_ses.addrstring);
	send_msg_userauth_failure(0, 1);
	}
	m_free(fp);

	out:
	/* cleanup stuff */
	if (signbuf) {
	buf_free(signbuf);
	}
	if (algo) {
	m_free(algo);
	}
	if (key) {
	sign_key_free(key);
	key = NULL;
	}
	TRACE(("leave pubkeyauth"))
	}

	/* Reply that the key is valid for auth, this is sent when the user sends
	* a straight copy of their pubkey to test, to avoid having to perform
	* expensive signing operations with a worthless key */
	static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
	unsigned char* keyblob, unsigned int keybloblen) {

	TRACE(("enter send_msg_userauth_pk_ok"))
	CHECKCLEARTOWRITE();

	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_PK_OK);
	buf_putstring(ses.writepayload, algo, algolen);
	buf_putstring(ses.writepayload, keyblob, keybloblen);

	encrypt_packet();
	TRACE(("leave send_msg_userauth_pk_ok"))

	}

	/* Checks whether a specified publickey (and associated algorithm) is an
	* acceptable key for authentication */
	/* Returns DROPBEAR_SUCCESS if key is ok for auth, DROPBEAR_FAILURE otherwise */
	static int checkpubkey(unsigned char* algo, unsigned int algolen,
	unsigned char* keyblob, unsigned int keybloblen) {

	FILE * authfile = NULL;
	char * filename = NULL;
	int ret = DROPBEAR_FAILURE;
	buffer * line = NULL;
	unsigned int len, pos;
	buffer * options_buf = NULL;
	int line_num;

	TRACE(("enter checkpubkey"))

	/* check that we can use the algo */
	if (have_algo(algo, algolen, sshhostkey) == DROPBEAR_FAILURE) {
	dropbear_log(LOG_WARNING,
	"Pubkey auth attempt with unknown algo for '%s' from %s",
	ses.authstate.pw_name, svr_ses.addrstring);
	goto out;
	}

	/* check file permissions, also whether file exists */
	if (checkpubkeyperms() == DROPBEAR_FAILURE) {
	TRACE(("bad authorized_keys permissions, or file doesn't exist"))
	goto out;
	}

	/* we don't need to check pw and pw_dir for validity, since
	* its been done in checkpubkeyperms. */
	len = strlen(ses.authstate.pw_dir);
	/* allocate max required pathname storage,
	* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
	filename = m_malloc(len + 22);
	snprintf(filename, len + 22, "%s/.ssh/authorized_keys",
	ses.authstate.pw_dir);

	/* open the file */
	authfile = fopen(filename, "r");
	if (authfile == NULL) {
	goto out;
	}
	TRACE(("checkpubkey: opened authorized_keys OK"))

	line = buf_new(MAX_AUTHKEYS_LINE);
	line_num = 0;

	/* iterate through the lines */
	do {
	/* new line : potentially new options */
	if (options_buf) {
	buf_free(options_buf);
	options_buf = NULL;
	}

	if (buf_getline(line, authfile) == DROPBEAR_FAILURE) {
	/* EOF reached */
	TRACE(("checkpubkey: authorized_keys EOF reached"))
	break;
	}
	line_num++;

	if (line->len < MIN_AUTHKEYS_LINE) {
	TRACE(("checkpubkey: line too short"))
	continue; /* line is too short for it to be a valid key */
	}

	/* check the key type - will fail if there are options */
	TRACE(("a line!"))

	if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
	int is_comment = 0;
	char *options_start = NULL;
	int options_len = 0;
	int escape, quoted;

	/* skip over any comments or leading whitespace */
	while (line->pos < line->len) {
	const char c = buf_getbyte(line);
	if (c == ' ' \|\| c == '\t') {
	continue;
	} else if (c == '#') {
	is_comment = 1;
	break;
	}
	buf_incrpos(line, -1);
	break;
	}
	if (is_comment) {
	/* next line */
	continue;
	}

	/* remember start of options */
	options_start = buf_getptr(line, 1);
	quoted = 0;
	escape = 0;
	options_len = 0;

	/* figure out where the options are */
	while (line->pos < line->len) {
	const char c = buf_getbyte(line);
	if (!quoted && (c == ' ' \|\| c == '\t')) {
	break;
	}
	escape = (!escape && c == '\\');
	if (!escape && c == '"') {
	quoted = !quoted;
	}
	options_len++;
	}
	options_buf = buf_new(options_len);
	buf_putbytes(options_buf, options_start, options_len);

	/* compare the algorithm */
	if (line->pos + algolen > line->len) {
	continue;
	}
	if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
	continue;
	}
	}
	buf_incrpos(line, algolen);

	/* check for space (' ') character */
	if (buf_getbyte(line) != ' ') {
	TRACE(("checkpubkey: space character expected, isn't there"))
	continue;
	}

	/* truncate the line at the space after the base64 data */
	pos = line->pos;
	for (len = 0; line->pos < line->len; len++) {
	if (buf_getbyte(line) == ' ') break;
	}
	buf_setpos(line, pos);
	buf_setlen(line, line->pos + len);

	TRACE(("checkpubkey: line pos = %d len = %d", line->pos, line->len))

	ret = cmp_base64_key(keyblob, keybloblen, algo, algolen, line, NULL);

	if (ret == DROPBEAR_SUCCESS && options_buf) {
	ret = svr_add_pubkey_options(options_buf, line_num, filename);
	}

	if (ret == DROPBEAR_SUCCESS) {
	break;
	}

	/* We continue to the next line otherwise */

	} while (1);

	out:
	if (authfile) {
	fclose(authfile);
	}
	if (line) {
	buf_free(line);
	}
	m_free(filename);
	if (options_buf) {
	buf_free(options_buf);
	}
	TRACE(("leave checkpubkey: ret=%d", ret))
	return ret;
	}


	/* Returns DROPBEAR_SUCCESS if file permissions for pubkeys are ok,
	* DROPBEAR_FAILURE otherwise.
	* Checks that the user's homedir, ~/.ssh, and
	* ~/.ssh/authorized_keys are all owned by either root or the user, and are
	* g-w, o-w */
	static int checkpubkeyperms() {

	char* filename = NULL;
	int ret = DROPBEAR_FAILURE;
	unsigned int len;

	TRACE(("enter checkpubkeyperms"))

	if (ses.authstate.pw_dir == NULL) {
	goto out;
	}

	if ((len = strlen(ses.authstate.pw_dir)) == 0) {
	goto out;
	}

	/* allocate max required pathname storage,
	* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
	filename = m_malloc(len + 22);
	strncpy(filename, ses.authstate.pw_dir, len+1);

	/* check ~ */
	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
	goto out;
	}

	/* check ~/.ssh */
	strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */
	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
	goto out;
	}

	/* now check ~/.ssh/authorized_keys */
	strncat(filename, "/authorized_keys", 16);
	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
	goto out;
	}

	/* file looks ok, return success */
	ret = DROPBEAR_SUCCESS;

	out:
	m_free(filename);

	TRACE(("leave checkpubkeyperms"))
	return ret;
	}

	/* Checks that a file is owned by the user or root, and isn't writable by
	* group or other */
	/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
	static int checkfileperm(char * filename) {
	struct stat filestat;
	int badperm = 0;

	TRACE(("enter checkfileperm(%s)", filename))

	if (stat(filename, &filestat) != 0) {
	TRACE(("leave checkfileperm: stat() != 0"))
	return DROPBEAR_FAILURE;
	}
	/* check ownership - user or root only*/
	if (filestat.st_uid != ses.authstate.pw_uid
	&& filestat.st_uid != 0) {
	badperm = 1;
	TRACE(("wrong ownership"))
	}
	/* check permissions - don't want group or others +w */
	if (filestat.st_mode & (S_IWGRP \| S_IWOTH)) {
	badperm = 1;
	TRACE(("wrong perms"))
	}
	if (badperm) {
	if (!ses.authstate.perm_warn) {
	ses.authstate.perm_warn = 1;
	dropbear_log(LOG_INFO, "%s must be owned by user or root, and not writable by others", filename);
	}
	TRACE(("leave checkfileperm: failure perms/owner"))
	return DROPBEAR_FAILURE;
	}

	TRACE(("leave checkfileperm: success"))
	return DROPBEAR_SUCCESS;
	}

	#endif