view cli-kex.c @ 447:278805938dcf

Patch from Nicolai Ehemann to try binding before going to the background, so that if it exits early (because something's already listening etc) then it will return an exitcode of 1.
author Matt Johnston <matt@ucc.asn.au>
date Thu, 19 Jul 2007 15:54:18 +0000
parents 91939c8c2572
children 9e51707cd6f2 76097ec1a29a
line wrap: on
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/*
 * Dropbear - a SSH2 server
 * 
 * Copyright (c) 2002-2004 Matt Johnston
 * Copyright (c) 2004 by Mihnea Stoenescu
 * 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. */

#include "includes.h"
#include "session.h"
#include "dbutil.h"
#include "algo.h"
#include "buffer.h"
#include "session.h"
#include "kex.h"
#include "ssh.h"
#include "packet.h"
#include "bignum.h"
#include "random.h"
#include "runopts.h"
#include "signkey.h"


static void checkhostkey(unsigned char* keyblob, unsigned int keybloblen);
#define MAX_KNOWNHOSTS_LINE 4500

void send_msg_kexdh_init() {

	cli_ses.dh_e = (mp_int*)m_malloc(sizeof(mp_int));
	cli_ses.dh_x = (mp_int*)m_malloc(sizeof(mp_int));
	m_mp_init_multi(cli_ses.dh_e, cli_ses.dh_x, NULL);

	gen_kexdh_vals(cli_ses.dh_e, cli_ses.dh_x);

	CHECKCLEARTOWRITE();
	buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_INIT);
	buf_putmpint(ses.writepayload, cli_ses.dh_e);
	encrypt_packet();
	ses.requirenext = SSH_MSG_KEXDH_REPLY;
}

/* Handle a diffie-hellman key exchange reply. */
void recv_msg_kexdh_reply() {

	DEF_MP_INT(dh_f);
	sign_key *hostkey = NULL;
	unsigned int type, keybloblen;
	unsigned char* keyblob = NULL;


	TRACE(("enter recv_msg_kexdh_reply"))

	if (cli_ses.kex_state != KEXDH_INIT_SENT) {
		dropbear_exit("Received out-of-order kexdhreply");
	}
	m_mp_init(&dh_f);
	type = ses.newkeys->algo_hostkey;
	TRACE(("type is %d", type))

	hostkey = new_sign_key();
	keybloblen = buf_getint(ses.payload);

	keyblob = buf_getptr(ses.payload, keybloblen);
	if (!ses.kexstate.donefirstkex) {
		/* Only makes sense the first time */
		checkhostkey(keyblob, keybloblen);
	}

	if (buf_get_pub_key(ses.payload, hostkey, &type) != DROPBEAR_SUCCESS) {
		TRACE(("failed getting pubkey"))
		dropbear_exit("Bad KEX packet");
	}

	if (buf_getmpint(ses.payload, &dh_f) != DROPBEAR_SUCCESS) {
		TRACE(("failed getting mpint"))
		dropbear_exit("Bad KEX packet");
	}

	kexdh_comb_key(cli_ses.dh_e, cli_ses.dh_x, &dh_f, hostkey);
	mp_clear(&dh_f);
	mp_clear_multi(cli_ses.dh_e, cli_ses.dh_x, NULL);
	m_free(cli_ses.dh_e);
	m_free(cli_ses.dh_x);

	if (buf_verify(ses.payload, hostkey, ses.hash, SHA1_HASH_SIZE) 
			!= DROPBEAR_SUCCESS) {
		dropbear_exit("Bad hostkey signature");
	}

	sign_key_free(hostkey);
	hostkey = NULL;

	send_msg_newkeys();
	ses.requirenext = SSH_MSG_NEWKEYS;
	TRACE(("leave recv_msg_kexdh_init"))
}

static void ask_to_confirm(unsigned char* keyblob, unsigned int keybloblen) {

	char* fp = NULL;
	FILE *tty = NULL;
	char response = 'z';

	fp = sign_key_fingerprint(keyblob, keybloblen);
	if (cli_opts.always_accept_key) {
		fprintf(stderr, "\nHost '%s' key accepted unconditionally.\n(fingerprint %s)\n",
				cli_opts.remotehost,
				fp);
		m_free(fp);
		return;
	}
	fprintf(stderr, "\nHost '%s' is not in the trusted hosts file.\n(fingerprint %s)\nDo you want to continue connecting? (y/n) ", 
			cli_opts.remotehost, 
			fp);
	m_free(fp);

	tty = fopen(_PATH_TTY, "r");
	if (tty) {
		response = getc(tty);
		fclose(tty);
	} else {
		response = getc(stdin);
	}

	if (response == 'y') {
		return;
	}

	dropbear_exit("Didn't validate host key");
}

static FILE* open_known_hosts_file(int * readonly)
{
	FILE * hostsfile = NULL;
	char * filename = NULL;
	char * homedir = NULL;
	
	homedir = getenv("HOME");

	if (!homedir) {
		struct passwd * pw = NULL;
		pw = getpwuid(getuid());
		if (pw) {
			homedir = pw->pw_dir;
		}
	}

	if (homedir) {
		unsigned int len;
		len = strlen(homedir);
		filename = m_malloc(len + 18); /* "/.ssh/known_hosts" and null-terminator*/

		snprintf(filename, len+18, "%s/.ssh", homedir);
		/* Check that ~/.ssh exists - easiest way is just to mkdir */
		if (mkdir(filename, S_IRWXU) != 0) {
			if (errno != EEXIST) {
				dropbear_log(LOG_INFO, "Warning: failed creating %s/.ssh: %s",
						homedir, strerror(errno));
				TRACE(("mkdir didn't work: %s", strerror(errno)))
				goto out;
			}
		}

		snprintf(filename, len+18, "%s/.ssh/known_hosts", homedir);
		hostsfile = fopen(filename, "a+");
		
		if (hostsfile != NULL) {
			*readonly = 0;
			fseek(hostsfile, 0, SEEK_SET);
		} else {
			/* We mightn't have been able to open it if it was read-only */
			if (errno == EACCES || errno == EROFS) {
					TRACE(("trying readonly: %s", strerror(errno)))
					*readonly = 1;
					hostsfile = fopen(filename, "r");
			}
		}
	}

	if (hostsfile == NULL) {
		TRACE(("hostsfile didn't open: %s", strerror(errno)))
		dropbear_log(LOG_WARNING, "Failed to open %s/.ssh/known_hosts",
				homedir);
		goto out;
	}	

out:
	m_free(filename);
	return hostsfile;
}

static void checkhostkey(unsigned char* keyblob, unsigned int keybloblen) {

	FILE *hostsfile = NULL;
	int readonly = 0;
	unsigned int hostlen, algolen;
	unsigned long len;
	const char *algoname = NULL;
	char * fingerprint = NULL;
	buffer * line = NULL;
	int ret;

	hostsfile = open_known_hosts_file(&readonly);
	if (!hostsfile)	{
		ask_to_confirm(keyblob, keybloblen);
		/* ask_to_confirm will exit upon failure */
		return;
	}
	
	line = buf_new(MAX_KNOWNHOSTS_LINE);
	hostlen = strlen(cli_opts.remotehost);
	algoname = signkey_name_from_type(ses.newkeys->algo_hostkey, &algolen);

	do {
		if (buf_getline(line, hostsfile) == DROPBEAR_FAILURE) {
			TRACE(("failed reading line: prob EOF"))
			break;
		}

		/* The line is too short to be sensible */
		/* "30" is 'enough to hold ssh-dss plus the spaces, ie so we don't
		 * buf_getfoo() past the end and die horribly - the base64 parsing
		 * code is what tiptoes up to the end nicely */
		if (line->len < (hostlen+30) ) {
			TRACE(("line is too short to be sensible"))
			continue;
		}

		/* Compare hostnames */
		if (strncmp(cli_opts.remotehost, buf_getptr(line, hostlen),
					hostlen) != 0) {
			TRACE(("hosts don't match"))
			continue;
		}

		buf_incrpos(line, hostlen);
		if (buf_getbyte(line) != ' ') {
			/* there wasn't a space after the hostname, something dodgy */
			TRACE(("missing space afte matching hostname"))
			continue;
		}

		if (strncmp(buf_getptr(line, algolen), algoname, algolen) != 0) {
			TRACE(("algo doesn't match"))
			continue;
		}

		buf_incrpos(line, algolen);
		if (buf_getbyte(line) != ' ') {
			TRACE(("missing space after algo"))
			continue;
		}

		/* Now we're at the interesting hostkey */
		ret = cmp_base64_key(keyblob, keybloblen, algoname, algolen,
						line, &fingerprint);

		if (ret == DROPBEAR_SUCCESS) {
			/* Good matching key */
			TRACE(("good matching key"))
			goto out;
		}

		/* The keys didn't match. eep. Note that we're "leaking"
		   the fingerprint strings here, but we're exiting anyway */
		dropbear_exit("\n\nHost key mismatch for %s !\n"
					"Fingerprint is %s\n"
					"Expected %s\n"
					"If you know that the host key is correct you can\nremove the bad entry from ~/.ssh/known_hosts", 
					cli_opts.remotehost,
					sign_key_fingerprint(keyblob, keybloblen),
					fingerprint ? fingerprint : "UNKNOWN");
	} while (1); /* keep going 'til something happens */

	/* Key doesn't exist yet */
	ask_to_confirm(keyblob, keybloblen);

	/* If we get here, they said yes */

	if (readonly) {
		TRACE(("readonly"))
		goto out;
	}

	if (!cli_opts.always_accept_key) {
		/* put the new entry in the file */
		fseek(hostsfile, 0, SEEK_END); /* In case it wasn't opened append */
		buf_setpos(line, 0);
		buf_setlen(line, 0);
		buf_putbytes(line, ses.remotehost, hostlen);
		buf_putbyte(line, ' ');
		buf_putbytes(line, algoname, algolen);
		buf_putbyte(line, ' ');
		len = line->size - line->pos;
		TRACE(("keybloblen %d, len %d", keybloblen, len))
		/* The only failure with base64 is buffer_overflow, but buf_getwriteptr
		 * will die horribly in the case anyway */
		base64_encode(keyblob, keybloblen, buf_getwriteptr(line, len), &len);
		buf_incrwritepos(line, len);
		buf_putbyte(line, '\n');
		buf_setpos(line, 0);
		fwrite(buf_getptr(line, line->len), line->len, 1, hostsfile);
		/* We ignore errors, since there's not much we can do about them */
	}

out:
	if (hostsfile != NULL) {
		fclose(hostsfile);
	}
	if (line != NULL) {
		buf_free(line);
	}
}