dropbear/cli-agentfwd.c

/*
 * Dropbear - a SSH2 server
 * 
 * Copyright (c) 2005 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. */

/* The basic protocol use to communicate with the agent is defined in
 * draft-ylonen-ssh-protocol-00.txt, with the ssh2 extensions defined through
 * openssh's implementation. */

#include "includes.h"

#ifdef ENABLE_CLI_AGENTFWD

#include "agentfwd.h"
#include "session.h"
#include "ssh.h"
#include "dbutil.h"
#include "chansession.h"
#include "channel.h"
#include "packet.h"
#include "buffer.h"
#include "random.h"
#include "listener.h"
#include "runopts.h"
#include "atomicio.h"
#include "signkey.h"
#include "auth.h"

static int new_agent_chan(struct Channel * channel);

const struct ChanType cli_chan_agent = {
	0, /* sepfds */
	"auth-agent@openssh.com",
	new_agent_chan,
	NULL,
	NULL,
	NULL
};

static int connect_agent() {

	int fd = -1;
	char* agent_sock = NULL;

	agent_sock = getenv("SSH_AUTH_SOCK");
	if (agent_sock == NULL)
		return -1;

	fd = connect_unix(agent_sock);

	return fd;
}

// handle a request for a connection to the locally running ssh-agent
// or forward.
static int new_agent_chan(struct Channel * channel) {

	int fd = -1;

	if (!cli_opts.agent_fwd)
		return SSH_OPEN_ADMINISTRATIVELY_PROHIBITED;

	fd = connect_agent();

	setnonblocking(fd);

	ses.maxfd = MAX(ses.maxfd, fd);

	channel->readfd = fd;
	channel->writefd = fd;

	// success
	return 0;
}

/* Sends a request to the agent, returning a newly allocated buffer
 * with the response */
/* Packet format (from draft-ylonen)
   4 bytes     Length, msb first.  Does not include length itself.
   1 byte      Packet type.  The value 255 is reserved for future extensions.
   data        Any data, depending on packet type.  Encoding as in the ssh packet
   protocol.

 In this case, data is always empty
*/
static buffer * agent_request(int fd, unsigned char type) {

	buffer * payload = NULL;
	buffer * inbuf = NULL;
	size_t readlen = 0;
	ssize_t ret;

	payload = buf_new(4 + 1);

	buf_putint(payload, 1);
	buf_putbyte(payload, type);

	ret = atomicio(write, fd, buf_getptr(payload, payload->len), payload->len);
	if ((size_t)ret != payload->len) {
		TRACE(("write failed for agent_request"))
		goto out;
	}

	buf_free(payload);
	payload = NULL;

	/* Now we read the response */
	inbuf = buf_new(4);
	ret = atomicio(read, fd, buf_getwriteptr(inbuf, 4), 4);
	if (ret != 4) {
		TRACE(("read of length failed for agent_request"))
		goto out;
	}

	readlen = buf_getint(inbuf);
	if (readlen > MAX_AGENT_REPLY) {
		TRACE(("agent reply is too big"));
		goto out;
	}

	buf_resize(inbuf, readlen);
	ret = atomicio(read, fd, buf_getwriteptr(inbuf, readlen), readlen);
	if ((size_t)ret != readlen) {
		TRACE(("read of data failed for agent_request"))
		goto out;
	}

out:
	if (payload)
		buf_free(payload);

	return inbuf;
}

static struct SignKeyList * agent_get_key_list(int fd)
{
	buffer * inbuf = NULL;
	unsigned int num = 0;
	unsigned char packet_type;
	unsigned int i;
	struct SignKeyList *retkey = NULL, *key = NULL;
	int ret;

	inbuf = agent_request(fd, SSH2_AGENTC_REQUEST_IDENTITIES);
	if (!inbuf) {
		goto out;
	}

	/* The reply has a format of:
	 * byte     packet_type
	 * int      num_keys
	 *
	 * string    keyblob1
	 * string    comment1
	 * ...
	 * string    keyblob(n)
	 * string    comment(n)
	 */
	packet_type = buf_getbyte(inbuf);
	if (packet_type != SSH2_AGENT_IDENTITIES_ANSWER) {
		goto out;
	}

	num = buf_getint(inbuf);
	for (i = 0; i < num; i++) {
		sign_key * pubkey = NULL;
		int key_type = DROPBEAR_SIGNKEY_ANY;
		struct SignKeyList *nextkey = NULL;

		nextkey = (struct SignKeyList*)m_malloc(sizeof(struct SignKeyList));
		if (key)
			key->next = nextkey;
		else
			retkey = nextkey;
		key = nextkey;

		pubkey = new_sign_key();
		ret = buf_get_pub_key(inbuf, pubkey, &key_type);
		if (ret != DROPBEAR_SUCCESS) {
			/* This is slack, properly would cleanup vars etc */
			dropbear_exit("Bad pubkey received from agent");
		}

		key->key = pubkey;
		key->next = NULL;
		key->type = key_type;
		key->source = SIGNKEY_SOURCE_AGENT;

		/* We'll ignore the comment */
		buf_eatstring(inbuf);
	}

out:
	if (inbuf) {
		buf_free(inbuf);
		inbuf = NULL;
	}

	return retkey;
}

void load_agent_keys()
{

	struct SignKeyList * ret_list;
	int fd;
	fd = connect_agent();
	if (fd < 0) {
		dropbear_log(LOG_INFO, "Failed to connect to agent");
		return;
	}

	ret_list =  agent_get_key_list(fd);
	close(fd);
}
	
// general procedure:
// - get the list of keys from the agent
// - foreach, send a dummy userauth_pubkey message to the server and see
// if it lets us in
// - if it does, sign and auth
// - if not, repeat.
//

#endif