auth2-pubkey.c - third_party/openssh-portable - Git at Google

 /*
  * 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"
 RCSID("$OpenBSD: auth2-pubkey.c,v 1.2 2002/05/31 11:35:15 markus Exp $");

 #include "ssh2.h"
 #include "xmalloc.h"
 #include "packet.h"
 #include "buffer.h"
 #include "log.h"
 #include "servconf.h"
 #include "compat.h"
 #include "bufaux.h"
 #include "auth.h"
 #include "key.h"
 #include "pathnames.h"
 #include "uidswap.h"
 #include "auth-options.h"
 #include "canohost.h"
 #include "monitor_wrap.h"

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

 static int
 userauth_pubkey(Authctxt *authctxt)
 {
 	Buffer b;
 	Key *key = NULL;
 	char *pkalg;
 	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 */
 		log("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 (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);
 		buffer_put_cstring(&b, authctxt->user);
 		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
 		/* 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;
 		buffer_clear(&b);
 		xfree(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);
 	xfree(pkalg);
 	xfree(pkblob);
 #ifdef HAVE_CYGWIN
 	if (check_nt_auth(0, authctxt->pw) == 0)
 		return(0);
 #endif
 	return authenticated;
 }

 /* return 1 if user allows given key */
 static int
 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 {
 	char line[8192];
 	int found_key = 0;
 	FILE *f;
 	u_long linenum = 0;
 	struct stat st;
 	Key *found;
 	char *fp;

 	if (pw == NULL)
 		return 0;

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

 	debug("trying public key file %s", file);

 	/* Fail quietly if file does not exist */
 	if (stat(file, &st) < 0) {
 		/* Restore the privileged uid. */
 		restore_uid();
 		return 0;
 	}
 	/* Open the file containing the authorized keys. */
 	f = fopen(file, "r");
 	if (!f) {
 		/* Restore the privileged uid. */
 		restore_uid();
 		return 0;
 	}
 	if (options.strict_modes &&
 	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 		fclose(f);
 		log("Authentication refused: %s", line);
 		restore_uid();
 		return 0;
 	}

 	found_key = 0;
 	found = key_new(key->type);

 	while (fgets(line, sizeof(line), f)) {
 		char *cp, *options = NULL;
 		linenum++;
 		/* 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);
 			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_equal(found, key) &&
 		    auth_parse_options(pw, options, file, linenum) == 1) {
 			found_key = 1;
 			debug("matching key found: file %s, line %lu",
 			    file, linenum);
 			fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 			verbose("Found matching %s key: %s",
 			    key_type(found), fp);
 			xfree(fp);
 			break;
 		}
 	}
 	restore_uid();
 	fclose(f);
 	key_free(found);
 	if (!found_key)
 		debug2("key not found");
 	return found_key;
 }

 /* check whether given key is in .ssh/authorized_keys* */
 int
 user_key_allowed(struct passwd *pw, Key *key)
 {
 	int success;
 	char *file;

 	file = authorized_keys_file(pw);
 	success = user_key_allowed2(pw, key, file);
 	xfree(file);
 	if (success)
 		return success;

 	/* try suffix "2" for backward compat, too */
 	file = authorized_keys_file2(pw);
 	success = user_key_allowed2(pw, key, file);
 	xfree(file);
 	return success;
 }

 Authmethod method_pubkey = {
 	"publickey",
 	userauth_pubkey,
 	&options.pubkey_authentication
 };
	/*
	* 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"
	RCSID("$OpenBSD: auth2-pubkey.c,v 1.2 2002/05/31 11:35:15 markus Exp $");

	#include "ssh2.h"
	#include "xmalloc.h"
	#include "packet.h"
	#include "buffer.h"
	#include "log.h"
	#include "servconf.h"
	#include "compat.h"
	#include "bufaux.h"
	#include "auth.h"
	#include "key.h"
	#include "pathnames.h"
	#include "uidswap.h"
	#include "auth-options.h"
	#include "canohost.h"
	#include "monitor_wrap.h"

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

	static int
	userauth_pubkey(Authctxt *authctxt)
	{
	Buffer b;
	Key *key = NULL;
	char *pkalg;
	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 */
	log("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 (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);
	buffer_put_cstring(&b, authctxt->user);
	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
	/* 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;
	buffer_clear(&b);
	xfree(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);
	xfree(pkalg);
	xfree(pkblob);
	#ifdef HAVE_CYGWIN
	if (check_nt_auth(0, authctxt->pw) == 0)
	return(0);
	#endif
	return authenticated;
	}

	/* return 1 if user allows given key */
	static int
	user_key_allowed2(struct passwd pw, Key key, char *file)
	{
	char line[8192];
	int found_key = 0;
	FILE *f;
	u_long linenum = 0;
	struct stat st;
	Key *found;
	char *fp;

	if (pw == NULL)
	return 0;

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

	debug("trying public key file %s", file);

	/* Fail quietly if file does not exist */
	if (stat(file, &st) < 0) {
	/* Restore the privileged uid. */
	restore_uid();
	return 0;
	}
	/* Open the file containing the authorized keys. */
	f = fopen(file, "r");
	if (!f) {
	/* Restore the privileged uid. */
	restore_uid();
	return 0;
	}
	if (options.strict_modes &&
	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
	fclose(f);
	log("Authentication refused: %s", line);
	restore_uid();
	return 0;
	}

	found_key = 0;
	found = key_new(key->type);

	while (fgets(line, sizeof(line), f)) {
	char cp, options = NULL;
	linenum++;
	/* 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);
	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_equal(found, key) &&
	auth_parse_options(pw, options, file, linenum) == 1) {
	found_key = 1;
	debug("matching key found: file %s, line %lu",
	file, linenum);
	fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
	verbose("Found matching %s key: %s",
	key_type(found), fp);
	xfree(fp);
	break;
	}
	}
	restore_uid();
	fclose(f);
	key_free(found);
	if (!found_key)
	debug2("key not found");
	return found_key;
	}

	/* check whether given key is in .ssh/authorized_keys* */
	int
	user_key_allowed(struct passwd pw, Key key)
	{
	int success;
	char *file;

	file = authorized_keys_file(pw);
	success = user_key_allowed2(pw, key, file);
	xfree(file);
	if (success)
	return success;

	/* try suffix "2" for backward compat, too */
	file = authorized_keys_file2(pw);
	success = user_key_allowed2(pw, key, file);
	xfree(file);
	return success;
	}

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