view cli-kex.c @ 1659:d32bcb5c557d

Add Ed25519 support (#91) * Add support for Ed25519 as a public key type Ed25519 is a elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance. It may be used for both user and host keys. OpenSSH key import and fuzzer are not supported yet. Initially inspired by Peter Szabo. * Add curve25519 and ed25519 fuzzers * Add import and export of Ed25519 keys
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Wed, 11 Mar 2020 21:09:45 +0500
parents 06d52bcb8094
children ba6fc7afe1c5
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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 "dbrandom.h"
#include "runopts.h"
#include "signkey.h"
#include "ecc.h"


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

void send_msg_kexdh_init() {
	TRACE(("send_msg_kexdh_init()"))	

	CHECKCLEARTOWRITE();
	buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_INIT);
	switch (ses.newkeys->algo_kex->mode) {
#if DROPBEAR_NORMAL_DH
		case DROPBEAR_KEX_NORMAL_DH:
			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
				|| !cli_ses.dh_param) {
				if (cli_ses.dh_param) {
					free_kexdh_param(cli_ses.dh_param);
				}
				cli_ses.dh_param = gen_kexdh_param();
			}
			buf_putmpint(ses.writepayload, &cli_ses.dh_param->pub);
			break;
#endif
#if DROPBEAR_ECDH
		case DROPBEAR_KEX_ECDH:
			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
				|| !cli_ses.ecdh_param) {
				if (cli_ses.ecdh_param) {
					free_kexecdh_param(cli_ses.ecdh_param);
				}
				cli_ses.ecdh_param = gen_kexecdh_param();
			}
			buf_put_ecc_raw_pubkey_string(ses.writepayload, &cli_ses.ecdh_param->key);
			break;
#endif
#if DROPBEAR_CURVE25519
		case DROPBEAR_KEX_CURVE25519:
			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
				|| !cli_ses.curve25519_param) {
				if (cli_ses.curve25519_param) {
					free_kexcurve25519_param(cli_ses.curve25519_param);
				}
				cli_ses.curve25519_param = gen_kexcurve25519_param();
			}
			buf_putstring(ses.writepayload, cli_ses.curve25519_param->pub, CURVE25519_LEN);
			break;
#endif
	}

	cli_ses.param_kex_algo = ses.newkeys->algo_kex;
	encrypt_packet();
}

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

	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");
	}
	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");
	}

	switch (ses.newkeys->algo_kex->mode) {
#if DROPBEAR_NORMAL_DH
		case DROPBEAR_KEX_NORMAL_DH:
			{
			DEF_MP_INT(dh_f);
			m_mp_init(&dh_f);
			if (buf_getmpint(ses.payload, &dh_f) != DROPBEAR_SUCCESS) {
				TRACE(("failed getting mpint"))
				dropbear_exit("Bad KEX packet");
			}

			kexdh_comb_key(cli_ses.dh_param, &dh_f, hostkey);
			mp_clear(&dh_f);
			}
			break;
#endif
#if DROPBEAR_ECDH
		case DROPBEAR_KEX_ECDH:
			{
			buffer *ecdh_qs = buf_getstringbuf(ses.payload);
			kexecdh_comb_key(cli_ses.ecdh_param, ecdh_qs, hostkey);
			buf_free(ecdh_qs);
			}
			break;
#endif
#if DROPBEAR_CURVE25519
		case DROPBEAR_KEX_CURVE25519:
			{
			buffer *ecdh_qs = buf_getstringbuf(ses.payload);
			kexcurve25519_comb_key(cli_ses.curve25519_param, ecdh_qs, hostkey);
			buf_free(ecdh_qs);
			}
			break;
#endif
	}

	if (cli_ses.dh_param) {
		free_kexdh_param(cli_ses.dh_param);
		cli_ses.dh_param = NULL;
	}
#if DROPBEAR_ECDH
	if (cli_ses.ecdh_param) {
		free_kexecdh_param(cli_ses.ecdh_param);
		cli_ses.ecdh_param = NULL;
	}
#endif
#if DROPBEAR_CURVE25519
	if (cli_ses.curve25519_param) {
		free_kexcurve25519_param(cli_ses.curve25519_param);
		cli_ses.curve25519_param = NULL;
	}
#endif

	cli_ses.param_kex_algo = NULL;
	if (buf_verify(ses.payload, hostkey, ses.hash) != 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(const unsigned char* keyblob, unsigned int keybloblen,
	const char* algoname) {

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

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

	if (cli_opts.no_hostkey_check) {
		dropbear_log(LOG_INFO, "Caution, skipping hostkey check for %s\n", cli_opts.remotehost);
		return;
	}

	algoname = signkey_name_from_type(ses.newkeys->algo_hostkey, &algolen);

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

	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, (const char *) buf_getptr(line, hostlen),
					hostlen) != 0) {
			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((const char *) 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, (const unsigned char *) 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\n%s host 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", 
					algoname,
					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, algoname);

	/* 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, (const unsigned char *) cli_opts.remotehost, hostlen);
		buf_putbyte(line, ' ');
		buf_putbytes(line, (const unsigned char *) algoname, algolen);
		buf_putbyte(line, ' ');
		len = line->size - line->pos;
		/* 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);
	}
	m_free(fingerprint);
}