packet.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. */

 #include "includes.h"
 #include "packet.h"
 #include "session.h"
 #include "dbutil.h"
 #include "ssh.h"
 #include "algo.h"
 #include "buffer.h"
 #include "kex.h"
 #include "random.h"
 #include "service.h"
 #include "auth.h"
 #include "channel.h"

 static int read_packet_init();
 static void make_mac(unsigned int seqno, const struct key_context_directional * key_state,
 		buffer * clear_buf, unsigned int clear_len,
 		unsigned char *output_mac);
 static int checkmac();

 #define ZLIB_COMPRESS_INCR 100
 #define ZLIB_DECOMPRESS_INCR 100
 #ifndef DISABLE_ZLIB
 static buffer* buf_decompress(buffer* buf, unsigned int len);
 static void buf_compress(buffer * dest, buffer * src, unsigned int len);
 #endif

 /* non-blocking function writing out a current encrypted packet */
 void write_packet() {

 	int len, written;
 	buffer * writebuf = NULL;
 	time_t now;
 	unsigned packet_type;

 	TRACE(("enter write_packet"))
 	dropbear_assert(!isempty(&ses.writequeue));

 	/* Get the next buffer in the queue of encrypted packets to write*/
 	writebuf = (buffer*)examine(&ses.writequeue);

 	/* The last byte of the buffer is not to be transmitted, but is
 	 * a cleartext packet_type indicator */
 	packet_type = writebuf->data[writebuf->len-1];
 	len = writebuf->len - 1 - writebuf->pos;
 	dropbear_assert(len > 0);
 	/* Try to write as much as possible */
 	written = write(ses.sock_out, buf_getptr(writebuf, len), len);

 	if (written < 0) {
 		if (errno == EINTR) {
 			TRACE(("leave writepacket: EINTR"))
 			return;
 		} else {
 			dropbear_exit("Error writing");
 		}
 	}

 	now = time(NULL);
 	ses.last_trx_packet_time = now;

 	if (packet_type != SSH_MSG_IGNORE) {
 		ses.last_packet_time = now;
 	}

 	if (written == 0) {
 		ses.remoteclosed();
 	}

 	if (written == len) {
 		/* We've finished with the packet, free it */
 		dequeue(&ses.writequeue);
 		buf_free(writebuf);
 		writebuf = NULL;
 	} else {
 		/* More packet left to write, leave it in the queue for later */
 		buf_incrpos(writebuf, written);
 	}

 	TRACE(("leave write_packet"))
 }

 /* Non-blocking function reading available portion of a packet into the
  * ses's buffer, decrypting the length if encrypted, decrypting the
  * full portion if possible */
 void read_packet() {

 	int len;
 	unsigned int maxlen;
 	unsigned char blocksize;

 	TRACE(("enter read_packet"))
 	blocksize = ses.keys->recv.algo_crypt->blocksize;

 	if (ses.readbuf == NULL || ses.readbuf->len < blocksize) {
 		int ret;
 		/* In the first blocksize of a packet */

 		/* Read the first blocksize of the packet, so we can decrypt it and
 		 * find the length of the whole packet */
 		ret = read_packet_init();

 		if (ret == DROPBEAR_FAILURE) {
 			/* didn't read enough to determine the length */
 			TRACE(("leave read_packet: packetinit done"))
 			return;
 		}
 	}

 	/* Attempt to read the remainder of the packet, note that there
 	 * mightn't be any available (EAGAIN) */
 	maxlen = ses.readbuf->len - ses.readbuf->pos;
 	len = read(ses.sock_in, buf_getptr(ses.readbuf, maxlen), maxlen);

 	if (len == 0) {
 		ses.remoteclosed();
 	}

 	if (len < 0) {
 		if (errno == EINTR || errno == EAGAIN) {
 			TRACE(("leave read_packet: EINTR or EAGAIN"))
 			return;
 		} else {
 			dropbear_exit("Error reading: %s", strerror(errno));
 		}
 	}

 	buf_incrpos(ses.readbuf, len);

 	if ((unsigned int)len == maxlen) {
 		/* The whole packet has been read */
 		decrypt_packet();
 		/* The main select() loop process_packet() to
 		 * handle the packet contents... */
 	}
 	TRACE(("leave read_packet"))
 }

 /* Function used to read the initial portion of a packet, and determine the
  * length. Only called during the first BLOCKSIZE of a packet. */
 /* Returns DROPBEAR_SUCCESS if the length is determined,
  * DROPBEAR_FAILURE otherwise */
 static int read_packet_init() {

 	unsigned int maxlen;
 	int slen;
 	unsigned int len;
 	unsigned int blocksize;
 	unsigned int macsize;


 	blocksize = ses.keys->recv.algo_crypt->blocksize;
 	macsize = ses.keys->recv.algo_mac->hashsize;

 	if (ses.readbuf == NULL) {
 		/* start of a new packet */
 		ses.readbuf = buf_new(INIT_READBUF);
 	}

 	maxlen = blocksize - ses.readbuf->pos;

 	/* read the rest of the packet if possible */
 	slen = read(ses.sock_in, buf_getwriteptr(ses.readbuf, maxlen),
 			maxlen);
 	if (slen == 0) {
 		ses.remoteclosed();
 	}
 	if (slen < 0) {
 		if (errno == EINTR) {
 			TRACE(("leave read_packet_init: EINTR"))
 			return DROPBEAR_FAILURE;
 		}
 		dropbear_exit("Error reading: %s", strerror(errno));
 	}

 	buf_incrwritepos(ses.readbuf, slen);

 	if ((unsigned int)slen != maxlen) {
 		/* don't have enough bytes to determine length, get next time */
 		return DROPBEAR_FAILURE;
 	}

 	/* now we have the first block, need to get packet length, so we decrypt
 	 * the first block (only need first 4 bytes) */
 	buf_setpos(ses.readbuf, 0);
 	if (ses.keys->recv.crypt_mode->decrypt(buf_getptr(ses.readbuf, blocksize),
 				buf_getwriteptr(ses.readbuf, blocksize),
 				blocksize,
 				&ses.keys->recv.cipher_state) != CRYPT_OK) {
 		dropbear_exit("Error decrypting");
 	}
 	len = buf_getint(ses.readbuf) + 4 + macsize;

 	TRACE(("packet size is %d, block %d mac %d", len, blocksize, macsize))


 	/* check packet length */
 	if ((len > RECV_MAX_PACKET_LEN) ||
 		(len < MIN_PACKET_LEN + macsize) ||
 		((len - macsize) % blocksize != 0)) {
 		dropbear_exit("Integrity error (bad packet size %d)", len);
 	}

 	if (len > ses.readbuf->size) {
 		buf_resize(ses.readbuf, len);
 	}
 	buf_setlen(ses.readbuf, len);
 	buf_setpos(ses.readbuf, blocksize);
 	return DROPBEAR_SUCCESS;
 }

 /* handle the received packet */
 void decrypt_packet() {

 	unsigned char blocksize;
 	unsigned char macsize;
 	unsigned int padlen;
 	unsigned int len;

 	TRACE(("enter decrypt_packet"))
 	blocksize = ses.keys->recv.algo_crypt->blocksize;
 	macsize = ses.keys->recv.algo_mac->hashsize;

 	ses.kexstate.datarecv += ses.readbuf->len;

 	/* we've already decrypted the first blocksize in read_packet_init */
 	buf_setpos(ses.readbuf, blocksize);

 	/* decrypt it in-place */
 	len = ses.readbuf->len - macsize - ses.readbuf->pos;
 	if (ses.keys->recv.crypt_mode->decrypt(
 				buf_getptr(ses.readbuf, len),
 				buf_getwriteptr(ses.readbuf, len),
 				len,
 				&ses.keys->recv.cipher_state) != CRYPT_OK) {
 		dropbear_exit("Error decrypting");
 	}
 	buf_incrpos(ses.readbuf, len);

 	/* check the hmac */
 	if (checkmac() != DROPBEAR_SUCCESS) {
 		dropbear_exit("Integrity error");
 	}

 	/* get padding length */
 	buf_setpos(ses.readbuf, PACKET_PADDING_OFF);
 	padlen = buf_getbyte(ses.readbuf);

 	/* payload length */
 	/* - 4 - 1 is for LEN and PADLEN values */
 	len = ses.readbuf->len - padlen - 4 - 1 - macsize;
 	if ((len > RECV_MAX_PAYLOAD_LEN) || (len < 1)) {
 		dropbear_exit("Bad packet size %d", len);
 	}

 	buf_setpos(ses.readbuf, PACKET_PAYLOAD_OFF);

 #ifndef DISABLE_ZLIB
 	if (is_compress_recv()) {
 		/* decompress */
 		ses.payload = buf_decompress(ses.readbuf, len);
 	} else
 #endif
 	{
 		/* copy payload */
 		ses.payload = buf_new(len);
 		memcpy(ses.payload->data, buf_getptr(ses.readbuf, len), len);
 		buf_incrlen(ses.payload, len);
 	}

 	buf_free(ses.readbuf);
 	ses.readbuf = NULL;
 	buf_setpos(ses.payload, 0);

 	ses.recvseq++;

 	TRACE(("leave decrypt_packet"))
 }

 /* Checks the mac at the end of a decrypted readbuf.
  * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
 static int checkmac() {

 	unsigned char mac_bytes[MAX_MAC_LEN];
 	unsigned int mac_size, contents_len;

 	mac_size = ses.keys->trans.algo_mac->hashsize;
 	contents_len = ses.readbuf->len - mac_size;

 	buf_setpos(ses.readbuf, 0);
 	make_mac(ses.recvseq, &ses.keys->recv, ses.readbuf, contents_len, mac_bytes);

 	/* compare the hash */
 	buf_setpos(ses.readbuf, contents_len);
 	if (memcmp(mac_bytes, buf_getptr(ses.readbuf, mac_size), mac_size) != 0) {
 		return DROPBEAR_FAILURE;
 	} else {
 		return DROPBEAR_SUCCESS;
 	}
 }

 #ifndef DISABLE_ZLIB
 /* returns a pointer to a newly created buffer */
 static buffer* buf_decompress(buffer* buf, unsigned int len) {

 	int result;
 	buffer * ret;
 	z_streamp zstream;

 	zstream = ses.keys->recv.zstream;
 	ret = buf_new(len);

 	zstream->avail_in = len;
 	zstream->next_in = buf_getptr(buf, len);

 	/* decompress the payload, incrementally resizing the output buffer */
 	while (1) {

 		zstream->avail_out = ret->size - ret->pos;
 		zstream->next_out = buf_getwriteptr(ret, zstream->avail_out);

 		result = inflate(zstream, Z_SYNC_FLUSH);

 		buf_setlen(ret, ret->size - zstream->avail_out);
 		buf_setpos(ret, ret->len);

 		if (result != Z_BUF_ERROR && result != Z_OK) {
 			dropbear_exit("zlib error");
 		}

 		if (zstream->avail_in == 0 &&
 		   		(zstream->avail_out != 0 || result == Z_BUF_ERROR)) {
 			/* we can only exit if avail_out hasn't all been used,
 			 * and there's no remaining input */
 			return ret;
 		}

 		if (zstream->avail_out == 0) {
 			buf_resize(ret, ret->size + ZLIB_DECOMPRESS_INCR);
 		}
 	}
 }
 #endif


 /* returns 1 if the packet is a valid type during kex (see 7.1 of rfc4253) */
 static int packet_is_okay_kex(unsigned char type) {
 	if (type >= SSH_MSG_USERAUTH_REQUEST) {
 		return 0;
 	}
 	if (type == SSH_MSG_SERVICE_REQUEST || type == SSH_MSG_SERVICE_ACCEPT) {
 		return 0;
 	}
 	if (type == SSH_MSG_KEXINIT) {
 		/* XXX should this die horribly if !dataallowed ?? */
 		return 0;
 	}
 	return 1;
 }

 static void enqueue_reply_packet() {
 	struct packetlist * new_item = NULL;
 	new_item = m_malloc(sizeof(struct packetlist));
 	new_item->next = NULL;

 	new_item->payload = buf_newcopy(ses.writepayload);
 	buf_setpos(ses.writepayload, 0);
 	buf_setlen(ses.writepayload, 0);

 	if (ses.reply_queue_tail) {
 		ses.reply_queue_tail->next = new_item;
 	} else {
 		ses.reply_queue_head = new_item;
 	}
 	ses.reply_queue_tail = new_item;
 	TRACE(("leave enqueue_reply_packet"))
 }

 void maybe_flush_reply_queue() {
 	struct packetlist *tmp_item = NULL, *curr_item = NULL;
 	if (!ses.dataallowed)
 	{
 		TRACE(("maybe_empty_reply_queue - no data allowed"))
 		return;
 	}

 	for (curr_item = ses.reply_queue_head; curr_item; ) {
 		CHECKCLEARTOWRITE();
 		buf_putbytes(ses.writepayload,
 			curr_item->payload->data, curr_item->payload->len);

 		buf_free(curr_item->payload);
 		tmp_item = curr_item;
 		curr_item = curr_item->next;
 		m_free(tmp_item);
 		encrypt_packet();
 	}
 	ses.reply_queue_head = ses.reply_queue_tail = NULL;
 }

 /* encrypt the writepayload, putting into writebuf, ready for write_packet()
  * to put on the wire */
 void encrypt_packet() {

 	unsigned char padlen;
 	unsigned char blocksize, mac_size;
 	buffer * writebuf; /* the packet which will go on the wire. This is
 	                      encrypted in-place. */
 	unsigned char packet_type;
 	unsigned int len, encrypt_buf_size;
 	unsigned char mac_bytes[MAX_MAC_LEN];

 	TRACE(("enter encrypt_packet()"))

 	buf_setpos(ses.writepayload, 0);
 	packet_type = buf_getbyte(ses.writepayload);
 	buf_setpos(ses.writepayload, 0);

 	TRACE(("encrypt_packet type is %d", packet_type))

 	if (!ses.dataallowed && !packet_is_okay_kex(packet_type)) {
 		/* During key exchange only particular packets are allowed.
 			Since this packet_type isn't OK we just enqueue it to send
 			after the KEX, see maybe_flush_reply_queue */
 		enqueue_reply_packet();
 		return;
 	}

 	blocksize = ses.keys->trans.algo_crypt->blocksize;
 	mac_size = ses.keys->trans.algo_mac->hashsize;

 	/* Encrypted packet len is payload+5. We need to then make sure
 	 * there is enough space for padding or MIN_PACKET_LEN.
 	 * Add extra 3 since we need at least 4 bytes of padding */
 	encrypt_buf_size = (ses.writepayload->len+4+1)
 		+ MAX(MIN_PACKET_LEN, blocksize) + 3
 	/* add space for the MAC at the end */
 				+ mac_size
 #ifndef DISABLE_ZLIB
 	/* some extra in case 'compression' makes it larger */
 				+ ZLIB_COMPRESS_INCR
 #endif
 	/* and an extra cleartext (stripped before transmission) byte for the
 	 * packet type */
 				+ 1;

 	writebuf = buf_new(encrypt_buf_size);
 	buf_setlen(writebuf, PACKET_PAYLOAD_OFF);
 	buf_setpos(writebuf, PACKET_PAYLOAD_OFF);

 #ifndef DISABLE_ZLIB
 	/* compression */
 	if (is_compress_trans()) {
 		int compress_delta;
 		buf_compress(writebuf, ses.writepayload, ses.writepayload->len);
 		compress_delta = (writebuf->len - PACKET_PAYLOAD_OFF) - ses.writepayload->len;

 		/* Handle the case where 'compress' increased the size. */
 		if (compress_delta > ZLIB_COMPRESS_INCR) {
 			buf_resize(writebuf, writebuf->size + compress_delta);
 		}
 	} else
 #endif
 	{
 		memcpy(buf_getwriteptr(writebuf, ses.writepayload->len),
 				buf_getptr(ses.writepayload, ses.writepayload->len),
 				ses.writepayload->len);
 		buf_incrwritepos(writebuf, ses.writepayload->len);
 	}

 	/* finished with payload */
 	buf_setpos(ses.writepayload, 0);
 	buf_setlen(ses.writepayload, 0);

 	/* length of padding - packet length must be a multiple of blocksize,
 	 * with a minimum of 4 bytes of padding */
 	padlen = blocksize - (writebuf->len) % blocksize;
 	if (padlen < 4) {
 		padlen += blocksize;
 	}
 	/* check for min packet length */
 	if (writebuf->len + padlen < MIN_PACKET_LEN) {
 		padlen += blocksize;
 	}

 	buf_setpos(writebuf, 0);
 	/* packet length excluding the packetlength uint32 */
 	buf_putint(writebuf, writebuf->len + padlen - 4);

 	/* padding len */
 	buf_putbyte(writebuf, padlen);
 	/* actual padding */
 	buf_setpos(writebuf, writebuf->len);
 	buf_incrlen(writebuf, padlen);
 	genrandom(buf_getptr(writebuf, padlen), padlen);

 	make_mac(ses.transseq, &ses.keys->trans, writebuf, writebuf->len, mac_bytes);

 	/* do the actual encryption, in-place */
 	buf_setpos(writebuf, 0);
 	/* encrypt it in-place*/
 	len = writebuf->len;
 	if (ses.keys->trans.crypt_mode->encrypt(
 				buf_getptr(writebuf, len),
 				buf_getwriteptr(writebuf, len),
 				len,
 				&ses.keys->trans.cipher_state) != CRYPT_OK) {
 		dropbear_exit("Error encrypting");
 	}
 	buf_incrpos(writebuf, len);

     /* stick the MAC on it */
     buf_putbytes(writebuf, mac_bytes, mac_size);

 	/* The last byte of the buffer stores the cleartext packet_type. It is not
 	 * transmitted but is used for transmit timeout purposes */
 	buf_putbyte(writebuf, packet_type);
 	/* enqueue the packet for sending. It will get freed after transmission. */
 	buf_setpos(writebuf, 0);
 	enqueue(&ses.writequeue, (void*)writebuf);

 	/* Update counts */
 	ses.kexstate.datatrans += writebuf->len;
 	ses.transseq++;

 	TRACE(("leave encrypt_packet()"))
 }


 /* Create the packet mac, and append H(seqno|clearbuf) to the output */
 /* output_mac must have ses.keys->trans.algo_mac->hashsize bytes. */
 static void make_mac(unsigned int seqno, const struct key_context_directional * key_state,
 		buffer * clear_buf, unsigned int clear_len,
 		unsigned char *output_mac) {
 	unsigned char seqbuf[4];
 	unsigned long bufsize;
 	hmac_state hmac;

 	TRACE(("enter writemac"))

 	if (key_state->algo_mac->hashsize > 0) {
 		/* calculate the mac */
 		if (hmac_init(&hmac,
 					key_state->hash_index,
 					key_state->mackey,
 					key_state->algo_mac->keysize) != CRYPT_OK) {
 			dropbear_exit("HMAC error");
 		}

 		/* sequence number */
 		STORE32H(seqno, seqbuf);
 		if (hmac_process(&hmac, seqbuf, 4) != CRYPT_OK) {
 			dropbear_exit("HMAC error");
 		}

 		/* the actual contents */
 		buf_setpos(clear_buf, 0);
 		if (hmac_process(&hmac,
 					buf_getptr(clear_buf, clear_len),
 					clear_len) != CRYPT_OK) {
 			dropbear_exit("HMAC error");
 		}

         bufsize = MAX_MAC_LEN;
 		if (hmac_done(&hmac, output_mac, &bufsize) != CRYPT_OK) {
 			dropbear_exit("HMAC error");
 		}
 	}
 	TRACE(("leave writemac"))
 }

 #ifndef DISABLE_ZLIB
 /* compresses len bytes from src, outputting to dest (starting from the
  * respective current positions. */
 static void buf_compress(buffer * dest, buffer * src, unsigned int len) {

 	unsigned int endpos = src->pos + len;
 	int result;

 	TRACE(("enter buf_compress"))

 	while (1) {

 		ses.keys->trans.zstream->avail_in = endpos - src->pos;
 		ses.keys->trans.zstream->next_in =
 			buf_getptr(src, ses.keys->trans.zstream->avail_in);

 		ses.keys->trans.zstream->avail_out = dest->size - dest->pos;
 		ses.keys->trans.zstream->next_out =
 			buf_getwriteptr(dest, ses.keys->trans.zstream->avail_out);

 		result = deflate(ses.keys->trans.zstream, Z_SYNC_FLUSH);

 		buf_setpos(src, endpos - ses.keys->trans.zstream->avail_in);
 		buf_setlen(dest, dest->size - ses.keys->trans.zstream->avail_out);
 		buf_setpos(dest, dest->len);

 		if (result != Z_OK) {
 			dropbear_exit("zlib error");
 		}

 		if (ses.keys->trans.zstream->avail_in == 0) {
 			break;
 		}

 		dropbear_assert(ses.keys->trans.zstream->avail_out == 0);

 		/* the buffer has been filled, we must extend. This only happens in
 		 * unusual circumstances where the data grows in size after deflate(),
 		 * but it is possible */
 		buf_resize(dest, dest->size + ZLIB_COMPRESS_INCR);

 	}
 	TRACE(("leave buf_compress"))
 }
 #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. */

	#include "includes.h"
	#include "packet.h"
	#include "session.h"
	#include "dbutil.h"
	#include "ssh.h"
	#include "algo.h"
	#include "buffer.h"
	#include "kex.h"
	#include "random.h"
	#include "service.h"
	#include "auth.h"
	#include "channel.h"

	static int read_packet_init();
	static void make_mac(unsigned int seqno, const struct key_context_directional * key_state,
	buffer * clear_buf, unsigned int clear_len,
	unsigned char *output_mac);
	static int checkmac();

	#define ZLIB_COMPRESS_INCR 100
	#define ZLIB_DECOMPRESS_INCR 100
	#ifndef DISABLE_ZLIB
	static buffer* buf_decompress(buffer* buf, unsigned int len);
	static void buf_compress(buffer * dest, buffer * src, unsigned int len);
	#endif

	/* non-blocking function writing out a current encrypted packet */
	void write_packet() {

	int len, written;
	buffer * writebuf = NULL;
	time_t now;
	unsigned packet_type;

	TRACE(("enter write_packet"))
	dropbear_assert(!isempty(&ses.writequeue));

	/* Get the next buffer in the queue of encrypted packets to write*/
	writebuf = (buffer*)examine(&ses.writequeue);

	/* The last byte of the buffer is not to be transmitted, but is
	* a cleartext packet_type indicator */
	packet_type = writebuf->data[writebuf->len-1];
	len = writebuf->len - 1 - writebuf->pos;
	dropbear_assert(len > 0);
	/* Try to write as much as possible */
	written = write(ses.sock_out, buf_getptr(writebuf, len), len);

	if (written < 0) {
	if (errno == EINTR) {
	TRACE(("leave writepacket: EINTR"))
	return;
	} else {
	dropbear_exit("Error writing");
	}
	}

	now = time(NULL);
	ses.last_trx_packet_time = now;

	if (packet_type != SSH_MSG_IGNORE) {
	ses.last_packet_time = now;
	}

	if (written == 0) {
	ses.remoteclosed();
	}

	if (written == len) {
	/* We've finished with the packet, free it */
	dequeue(&ses.writequeue);
	buf_free(writebuf);
	writebuf = NULL;
	} else {
	/* More packet left to write, leave it in the queue for later */
	buf_incrpos(writebuf, written);
	}

	TRACE(("leave write_packet"))
	}

	/* Non-blocking function reading available portion of a packet into the
	* ses's buffer, decrypting the length if encrypted, decrypting the
	* full portion if possible */
	void read_packet() {

	int len;
	unsigned int maxlen;
	unsigned char blocksize;

	TRACE(("enter read_packet"))
	blocksize = ses.keys->recv.algo_crypt->blocksize;

	if (ses.readbuf == NULL \|\| ses.readbuf->len < blocksize) {
	int ret;
	/* In the first blocksize of a packet */

	/* Read the first blocksize of the packet, so we can decrypt it and
	* find the length of the whole packet */
	ret = read_packet_init();

	if (ret == DROPBEAR_FAILURE) {
	/* didn't read enough to determine the length */
	TRACE(("leave read_packet: packetinit done"))
	return;
	}
	}

	/* Attempt to read the remainder of the packet, note that there
	* mightn't be any available (EAGAIN) */
	maxlen = ses.readbuf->len - ses.readbuf->pos;
	len = read(ses.sock_in, buf_getptr(ses.readbuf, maxlen), maxlen);

	if (len == 0) {
	ses.remoteclosed();
	}

	if (len < 0) {
	if (errno == EINTR \|\| errno == EAGAIN) {
	TRACE(("leave read_packet: EINTR or EAGAIN"))
	return;
	} else {
	dropbear_exit("Error reading: %s", strerror(errno));
	}
	}

	buf_incrpos(ses.readbuf, len);

	if ((unsigned int)len == maxlen) {
	/* The whole packet has been read */
	decrypt_packet();
	/* The main select() loop process_packet() to
	* handle the packet contents... */
	}
	TRACE(("leave read_packet"))
	}

	/* Function used to read the initial portion of a packet, and determine the
	* length. Only called during the first BLOCKSIZE of a packet. */
	/* Returns DROPBEAR_SUCCESS if the length is determined,
	* DROPBEAR_FAILURE otherwise */
	static int read_packet_init() {

	unsigned int maxlen;
	int slen;
	unsigned int len;
	unsigned int blocksize;
	unsigned int macsize;


	blocksize = ses.keys->recv.algo_crypt->blocksize;
	macsize = ses.keys->recv.algo_mac->hashsize;

	if (ses.readbuf == NULL) {
	/* start of a new packet */
	ses.readbuf = buf_new(INIT_READBUF);
	}

	maxlen = blocksize - ses.readbuf->pos;

	/* read the rest of the packet if possible */
	slen = read(ses.sock_in, buf_getwriteptr(ses.readbuf, maxlen),
	maxlen);
	if (slen == 0) {
	ses.remoteclosed();
	}
	if (slen < 0) {
	if (errno == EINTR) {
	TRACE(("leave read_packet_init: EINTR"))
	return DROPBEAR_FAILURE;
	}
	dropbear_exit("Error reading: %s", strerror(errno));
	}

	buf_incrwritepos(ses.readbuf, slen);

	if ((unsigned int)slen != maxlen) {
	/* don't have enough bytes to determine length, get next time */
	return DROPBEAR_FAILURE;
	}

	/* now we have the first block, need to get packet length, so we decrypt
	* the first block (only need first 4 bytes) */
	buf_setpos(ses.readbuf, 0);
	if (ses.keys->recv.crypt_mode->decrypt(buf_getptr(ses.readbuf, blocksize),
	buf_getwriteptr(ses.readbuf, blocksize),
	blocksize,
	&ses.keys->recv.cipher_state) != CRYPT_OK) {
	dropbear_exit("Error decrypting");
	}
	len = buf_getint(ses.readbuf) + 4 + macsize;

	TRACE(("packet size is %d, block %d mac %d", len, blocksize, macsize))


	/* check packet length */
	if ((len > RECV_MAX_PACKET_LEN) \|\|
	(len < MIN_PACKET_LEN + macsize) \|\|
	((len - macsize) % blocksize != 0)) {
	dropbear_exit("Integrity error (bad packet size %d)", len);
	}

	if (len > ses.readbuf->size) {
	buf_resize(ses.readbuf, len);
	}
	buf_setlen(ses.readbuf, len);
	buf_setpos(ses.readbuf, blocksize);
	return DROPBEAR_SUCCESS;
	}

	/* handle the received packet */
	void decrypt_packet() {

	unsigned char blocksize;
	unsigned char macsize;
	unsigned int padlen;
	unsigned int len;

	TRACE(("enter decrypt_packet"))
	blocksize = ses.keys->recv.algo_crypt->blocksize;
	macsize = ses.keys->recv.algo_mac->hashsize;

	ses.kexstate.datarecv += ses.readbuf->len;

	/* we've already decrypted the first blocksize in read_packet_init */
	buf_setpos(ses.readbuf, blocksize);

	/* decrypt it in-place */
	len = ses.readbuf->len - macsize - ses.readbuf->pos;
	if (ses.keys->recv.crypt_mode->decrypt(
	buf_getptr(ses.readbuf, len),
	buf_getwriteptr(ses.readbuf, len),
	len,
	&ses.keys->recv.cipher_state) != CRYPT_OK) {
	dropbear_exit("Error decrypting");
	}
	buf_incrpos(ses.readbuf, len);

	/* check the hmac */
	if (checkmac() != DROPBEAR_SUCCESS) {
	dropbear_exit("Integrity error");
	}

	/* get padding length */
	buf_setpos(ses.readbuf, PACKET_PADDING_OFF);
	padlen = buf_getbyte(ses.readbuf);

	/* payload length */
	/* - 4 - 1 is for LEN and PADLEN values */
	len = ses.readbuf->len - padlen - 4 - 1 - macsize;
	if ((len > RECV_MAX_PAYLOAD_LEN) \|\| (len < 1)) {
	dropbear_exit("Bad packet size %d", len);
	}

	buf_setpos(ses.readbuf, PACKET_PAYLOAD_OFF);

	#ifndef DISABLE_ZLIB
	if (is_compress_recv()) {
	/* decompress */
	ses.payload = buf_decompress(ses.readbuf, len);
	} else
	#endif
	{
	/* copy payload */
	ses.payload = buf_new(len);
	memcpy(ses.payload->data, buf_getptr(ses.readbuf, len), len);
	buf_incrlen(ses.payload, len);
	}

	buf_free(ses.readbuf);
	ses.readbuf = NULL;
	buf_setpos(ses.payload, 0);

	ses.recvseq++;

	TRACE(("leave decrypt_packet"))
	}

	/* Checks the mac at the end of a decrypted readbuf.
	* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
	static int checkmac() {

	unsigned char mac_bytes[MAX_MAC_LEN];
	unsigned int mac_size, contents_len;

	mac_size = ses.keys->trans.algo_mac->hashsize;
	contents_len = ses.readbuf->len - mac_size;

	buf_setpos(ses.readbuf, 0);
	make_mac(ses.recvseq, &ses.keys->recv, ses.readbuf, contents_len, mac_bytes);

	/* compare the hash */
	buf_setpos(ses.readbuf, contents_len);
	if (memcmp(mac_bytes, buf_getptr(ses.readbuf, mac_size), mac_size) != 0) {
	return DROPBEAR_FAILURE;
	} else {
	return DROPBEAR_SUCCESS;
	}
	}

	#ifndef DISABLE_ZLIB
	/* returns a pointer to a newly created buffer */
	static buffer* buf_decompress(buffer* buf, unsigned int len) {

	int result;
	buffer * ret;
	z_streamp zstream;

	zstream = ses.keys->recv.zstream;
	ret = buf_new(len);

	zstream->avail_in = len;
	zstream->next_in = buf_getptr(buf, len);

	/* decompress the payload, incrementally resizing the output buffer */
	while (1) {

	zstream->avail_out = ret->size - ret->pos;
	zstream->next_out = buf_getwriteptr(ret, zstream->avail_out);

	result = inflate(zstream, Z_SYNC_FLUSH);

	buf_setlen(ret, ret->size - zstream->avail_out);
	buf_setpos(ret, ret->len);

	if (result != Z_BUF_ERROR && result != Z_OK) {
	dropbear_exit("zlib error");
	}

	if (zstream->avail_in == 0 &&
	(zstream->avail_out != 0 \|\| result == Z_BUF_ERROR)) {
	/* we can only exit if avail_out hasn't all been used,
	* and there's no remaining input */
	return ret;
	}

	if (zstream->avail_out == 0) {
	buf_resize(ret, ret->size + ZLIB_DECOMPRESS_INCR);
	}
	}
	}
	#endif


	/* returns 1 if the packet is a valid type during kex (see 7.1 of rfc4253) */
	static int packet_is_okay_kex(unsigned char type) {
	if (type >= SSH_MSG_USERAUTH_REQUEST) {
	return 0;
	}
	if (type == SSH_MSG_SERVICE_REQUEST \|\| type == SSH_MSG_SERVICE_ACCEPT) {
	return 0;
	}
	if (type == SSH_MSG_KEXINIT) {
	/* XXX should this die horribly if !dataallowed ?? */
	return 0;
	}
	return 1;
	}

	static void enqueue_reply_packet() {
	struct packetlist * new_item = NULL;
	new_item = m_malloc(sizeof(struct packetlist));
	new_item->next = NULL;

	new_item->payload = buf_newcopy(ses.writepayload);
	buf_setpos(ses.writepayload, 0);
	buf_setlen(ses.writepayload, 0);

	if (ses.reply_queue_tail) {
	ses.reply_queue_tail->next = new_item;
	} else {
	ses.reply_queue_head = new_item;
	}
	ses.reply_queue_tail = new_item;
	TRACE(("leave enqueue_reply_packet"))
	}

	void maybe_flush_reply_queue() {
	struct packetlist tmp_item = NULL, curr_item = NULL;
	if (!ses.dataallowed)
	{
	TRACE(("maybe_empty_reply_queue - no data allowed"))
	return;
	}

	for (curr_item = ses.reply_queue_head; curr_item; ) {
	CHECKCLEARTOWRITE();
	buf_putbytes(ses.writepayload,
	curr_item->payload->data, curr_item->payload->len);

	buf_free(curr_item->payload);
	tmp_item = curr_item;
	curr_item = curr_item->next;
	m_free(tmp_item);
	encrypt_packet();
	}
	ses.reply_queue_head = ses.reply_queue_tail = NULL;
	}

	/* encrypt the writepayload, putting into writebuf, ready for write_packet()
	* to put on the wire */
	void encrypt_packet() {

	unsigned char padlen;
	unsigned char blocksize, mac_size;
	buffer * writebuf; /* the packet which will go on the wire. This is
	encrypted in-place. */
	unsigned char packet_type;
	unsigned int len, encrypt_buf_size;
	unsigned char mac_bytes[MAX_MAC_LEN];

	TRACE(("enter encrypt_packet()"))

	buf_setpos(ses.writepayload, 0);
	packet_type = buf_getbyte(ses.writepayload);
	buf_setpos(ses.writepayload, 0);

	TRACE(("encrypt_packet type is %d", packet_type))

	if (!ses.dataallowed && !packet_is_okay_kex(packet_type)) {
	/* During key exchange only particular packets are allowed.
	Since this packet_type isn't OK we just enqueue it to send
	after the KEX, see maybe_flush_reply_queue */
	enqueue_reply_packet();
	return;
	}

	blocksize = ses.keys->trans.algo_crypt->blocksize;
	mac_size = ses.keys->trans.algo_mac->hashsize;

	/* Encrypted packet len is payload+5. We need to then make sure
	* there is enough space for padding or MIN_PACKET_LEN.
	* Add extra 3 since we need at least 4 bytes of padding */
	encrypt_buf_size = (ses.writepayload->len+4+1)
	+ MAX(MIN_PACKET_LEN, blocksize) + 3
	/* add space for the MAC at the end */
	+ mac_size
	#ifndef DISABLE_ZLIB
	/* some extra in case 'compression' makes it larger */
	+ ZLIB_COMPRESS_INCR
	#endif
	/* and an extra cleartext (stripped before transmission) byte for the
	* packet type */
	+ 1;

	writebuf = buf_new(encrypt_buf_size);
	buf_setlen(writebuf, PACKET_PAYLOAD_OFF);
	buf_setpos(writebuf, PACKET_PAYLOAD_OFF);

	#ifndef DISABLE_ZLIB
	/* compression */
	if (is_compress_trans()) {
	int compress_delta;
	buf_compress(writebuf, ses.writepayload, ses.writepayload->len);
	compress_delta = (writebuf->len - PACKET_PAYLOAD_OFF) - ses.writepayload->len;

	/* Handle the case where 'compress' increased the size. */
	if (compress_delta > ZLIB_COMPRESS_INCR) {
	buf_resize(writebuf, writebuf->size + compress_delta);
	}
	} else
	#endif
	{
	memcpy(buf_getwriteptr(writebuf, ses.writepayload->len),
	buf_getptr(ses.writepayload, ses.writepayload->len),
	ses.writepayload->len);
	buf_incrwritepos(writebuf, ses.writepayload->len);
	}

	/* finished with payload */
	buf_setpos(ses.writepayload, 0);
	buf_setlen(ses.writepayload, 0);

	/* length of padding - packet length must be a multiple of blocksize,
	* with a minimum of 4 bytes of padding */
	padlen = blocksize - (writebuf->len) % blocksize;
	if (padlen < 4) {
	padlen += blocksize;
	}
	/* check for min packet length */
	if (writebuf->len + padlen < MIN_PACKET_LEN) {
	padlen += blocksize;
	}

	buf_setpos(writebuf, 0);
	/* packet length excluding the packetlength uint32 */
	buf_putint(writebuf, writebuf->len + padlen - 4);

	/* padding len */
	buf_putbyte(writebuf, padlen);
	/* actual padding */
	buf_setpos(writebuf, writebuf->len);
	buf_incrlen(writebuf, padlen);
	genrandom(buf_getptr(writebuf, padlen), padlen);

	make_mac(ses.transseq, &ses.keys->trans, writebuf, writebuf->len, mac_bytes);

	/* do the actual encryption, in-place */
	buf_setpos(writebuf, 0);
	/* encrypt it in-place*/
	len = writebuf->len;
	if (ses.keys->trans.crypt_mode->encrypt(
	buf_getptr(writebuf, len),
	buf_getwriteptr(writebuf, len),
	len,
	&ses.keys->trans.cipher_state) != CRYPT_OK) {
	dropbear_exit("Error encrypting");
	}
	buf_incrpos(writebuf, len);

	/* stick the MAC on it */
	buf_putbytes(writebuf, mac_bytes, mac_size);

	/* The last byte of the buffer stores the cleartext packet_type. It is not
	* transmitted but is used for transmit timeout purposes */
	buf_putbyte(writebuf, packet_type);
	/* enqueue the packet for sending. It will get freed after transmission. */
	buf_setpos(writebuf, 0);
	enqueue(&ses.writequeue, (void*)writebuf);

	/* Update counts */
	ses.kexstate.datatrans += writebuf->len;
	ses.transseq++;

	TRACE(("leave encrypt_packet()"))
	}


	/* Create the packet mac, and append H(seqno\|clearbuf) to the output */
	/* output_mac must have ses.keys->trans.algo_mac->hashsize bytes. */
	static void make_mac(unsigned int seqno, const struct key_context_directional * key_state,
	buffer * clear_buf, unsigned int clear_len,
	unsigned char *output_mac) {
	unsigned char seqbuf[4];
	unsigned long bufsize;
	hmac_state hmac;

	TRACE(("enter writemac"))

	if (key_state->algo_mac->hashsize > 0) {
	/* calculate the mac */
	if (hmac_init(&hmac,
	key_state->hash_index,
	key_state->mackey,
	key_state->algo_mac->keysize) != CRYPT_OK) {
	dropbear_exit("HMAC error");
	}

	/* sequence number */
	STORE32H(seqno, seqbuf);
	if (hmac_process(&hmac, seqbuf, 4) != CRYPT_OK) {
	dropbear_exit("HMAC error");
	}

	/* the actual contents */
	buf_setpos(clear_buf, 0);
	if (hmac_process(&hmac,
	buf_getptr(clear_buf, clear_len),
	clear_len) != CRYPT_OK) {
	dropbear_exit("HMAC error");
	}

	bufsize = MAX_MAC_LEN;
	if (hmac_done(&hmac, output_mac, &bufsize) != CRYPT_OK) {
	dropbear_exit("HMAC error");
	}
	}
	TRACE(("leave writemac"))
	}

	#ifndef DISABLE_ZLIB
	/* compresses len bytes from src, outputting to dest (starting from the
	* respective current positions. */
	static void buf_compress(buffer * dest, buffer * src, unsigned int len) {

	unsigned int endpos = src->pos + len;
	int result;

	TRACE(("enter buf_compress"))

	while (1) {

	ses.keys->trans.zstream->avail_in = endpos - src->pos;
	ses.keys->trans.zstream->next_in =
	buf_getptr(src, ses.keys->trans.zstream->avail_in);

	ses.keys->trans.zstream->avail_out = dest->size - dest->pos;
	ses.keys->trans.zstream->next_out =
	buf_getwriteptr(dest, ses.keys->trans.zstream->avail_out);

	result = deflate(ses.keys->trans.zstream, Z_SYNC_FLUSH);

	buf_setpos(src, endpos - ses.keys->trans.zstream->avail_in);
	buf_setlen(dest, dest->size - ses.keys->trans.zstream->avail_out);
	buf_setpos(dest, dest->len);

	if (result != Z_OK) {
	dropbear_exit("zlib error");
	}

	if (ses.keys->trans.zstream->avail_in == 0) {
	break;
	}

	dropbear_assert(ses.keys->trans.zstream->avail_out == 0);

	/* the buffer has been filled, we must extend. This only happens in
	* unusual circumstances where the data grows in size after deflate(),
	* but it is possible */
	buf_resize(dest, dest->size + ZLIB_COMPRESS_INCR);

	}
	TRACE(("leave buf_compress"))
	}
	#endif