packet.c

OpenSSH 是 SSH （Secure SHell） 协议的免费开源实现。它用安全、加密的网络连接工具代替了 telnet、ftp、 rlogin、rsh 和 rcp 工具。OpenSSH 支持

	u_int32_t rnd = 0;

	/*
	 * If using packet compression, compress the payload of the outgoing
	 * packet.
	 */
	if (packet_compression) {
		buffer_clear(&compression_buffer);
		/* Skip padding. */
		buffer_consume(&outgoing_packet, 8);
		/* padding */
		buffer_append(&compression_buffer, "\0\0\0\0\0\0\0\0", 8);
		buffer_compress(&outgoing_packet, &compression_buffer);
		buffer_clear(&outgoing_packet);
		buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
		    buffer_len(&compression_buffer));
	}
	/* Compute packet length without padding (add checksum, remove padding). */
	len = buffer_len(&outgoing_packet) + 4 - 8;

	/* Insert padding. Initialized to zero in packet_start1() */
	padding = 8 - len % 8;
	if (!send_context.plaintext) {
		cp = buffer_ptr(&outgoing_packet);
		for (i = 0; i < padding; i++) {
			if (i % 4 == 0)
				rnd = arc4random();
			cp[7 - i] = rnd & 0xff;
			rnd >>= 8;
		}
	}
	buffer_consume(&outgoing_packet, 8 - padding);

	/* Add check bytes. */
	checksum = ssh_crc32(buffer_ptr(&outgoing_packet),
	    buffer_len(&outgoing_packet));
	PUT_32BIT(buf, checksum);
	buffer_append(&outgoing_packet, buf, 4);

#ifdef PACKET_DEBUG
	fprintf(stderr, "packet_send plain: ");
	buffer_dump(&outgoing_packet);
#endif

	/* Append to output. */
	PUT_32BIT(buf, len);
	buffer_append(&output, buf, 4);
	cp = buffer_append_space(&output, buffer_len(&outgoing_packet));
	cipher_crypt(&send_context, cp, buffer_ptr(&outgoing_packet),
	    buffer_len(&outgoing_packet));

#ifdef PACKET_DEBUG
	fprintf(stderr, "encrypted: ");
	buffer_dump(&output);
#endif

	buffer_clear(&outgoing_packet);

	/*
	 * Note that the packet is now only buffered in output.  It won\'t be
	 * actually sent until packet_write_wait or packet_write_poll is
	 * called.
	 */
}

void
set_newkeys(int mode)
{
	Enc *enc;
	Mac *mac;
	Comp *comp;
	CipherContext *cc;
	u_int64_t *max_blocks;
	int crypt_type;

	debug2("set_newkeys: mode %d", mode);

	if (mode == MODE_OUT) {
		cc = &send_context;
		crypt_type = CIPHER_ENCRYPT;
		p_send.packets = p_send.blocks = 0;
		max_blocks = &max_blocks_out;
	} else {
		cc = &receive_context;
		crypt_type = CIPHER_DECRYPT;
		p_read.packets = p_read.blocks = 0;
		max_blocks = &max_blocks_in;
	}
	if (newkeys[mode] != NULL) {
		debug("set_newkeys: rekeying");
		cipher_cleanup(cc);
		enc  = &newkeys[mode]->enc;
		mac  = &newkeys[mode]->mac;
		comp = &newkeys[mode]->comp;
		memset(mac->key, 0, mac->key_len);
		xfree(enc->name);
		xfree(enc->iv);
		xfree(enc->key);
		xfree(mac->name);
		xfree(mac->key);
		xfree(comp->name);
		xfree(newkeys[mode]);
	}
	newkeys[mode] = kex_get_newkeys(mode);
	if (newkeys[mode] == NULL)
		fatal("newkeys: no keys for mode %d", mode);
	enc  = &newkeys[mode]->enc;
	mac  = &newkeys[mode]->mac;
	comp = &newkeys[mode]->comp;
	if (mac->md != NULL)
		mac->enabled = 1;
	DBG(debug("cipher_init_context: %d", mode));
	cipher_init(cc, enc->cipher, enc->key, enc->key_len,
	    enc->iv, enc->block_size, crypt_type);
	/* Deleting the keys does not gain extra security */
	/* memset(enc->iv,  0, enc->block_size);
	   memset(enc->key, 0, enc->key_len); */
	if (comp->type != 0 && comp->enabled == 0) {
		packet_init_compression();
		if (mode == MODE_OUT)
			buffer_compress_init_send(6);
		else
			buffer_compress_init_recv();
		comp->enabled = 1;
	}
	/*
	 * The 2^(blocksize*2) limit is too expensive for 3DES,
	 * blowfish, etc, so enforce a 1GB limit for small blocksizes.
	 */
	if (enc->block_size >= 16)
		*max_blocks = (u_int64_t)1 << (enc->block_size*2);
	else
		*max_blocks = ((u_int64_t)1 << 30) / enc->block_size;
	if (rekey_limit)
		*max_blocks = MIN(*max_blocks, rekey_limit / enc->block_size);
}

/*
 * Finalize packet in SSH2 format (compress, mac, encrypt, enqueue)
 */
static void
packet_send2_wrapped(void)
{
	u_char type, *cp, *macbuf = NULL;
	u_char padlen, pad;
	u_int packet_length = 0;
	u_int i, len;
	u_int32_t rnd = 0;
	Enc *enc   = NULL;
	Mac *mac   = NULL;
	Comp *comp = NULL;
	int block_size;

	if (newkeys[MODE_OUT] != NULL) {
		enc  = &newkeys[MODE_OUT]->enc;
		mac  = &newkeys[MODE_OUT]->mac;
		comp = &newkeys[MODE_OUT]->comp;
	}
	block_size = enc ? enc->block_size : 8;

	cp = buffer_ptr(&outgoing_packet);
	type = cp[5];

#ifdef PACKET_DEBUG
	fprintf(stderr, "plain:     ");
	buffer_dump(&outgoing_packet);
#endif

	if (comp && comp->enabled) {
		len = buffer_len(&outgoing_packet);
		/* skip header, compress only payload */
		buffer_consume(&outgoing_packet, 5);
		buffer_clear(&compression_buffer);
		buffer_compress(&outgoing_packet, &compression_buffer);
		buffer_clear(&outgoing_packet);
		buffer_append(&outgoing_packet, "\0\0\0\0\0", 5);
		buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
		    buffer_len(&compression_buffer));
		DBG(debug("compression: raw %d compressed %d", len,
		    buffer_len(&outgoing_packet)));
	}

	/* sizeof (packet_len + pad_len + payload) */
	len = buffer_len(&outgoing_packet);

	/*
	 * calc size of padding, alloc space, get random data,
	 * minimum padding is 4 bytes
	 */
	padlen = block_size - (len % block_size);
	if (padlen < 4)
		padlen += block_size;
	if (extra_pad) {
		/* will wrap if extra_pad+padlen > 255 */
		extra_pad  = roundup(extra_pad, block_size);
		pad = extra_pad - ((len + padlen) % extra_pad);
		debug3("packet_send2: adding %d (len %d padlen %d extra_pad %d)",
		    pad, len, padlen, extra_pad);
		padlen += pad;
		extra_pad = 0;
	}
	cp = buffer_append_space(&outgoing_packet, padlen);
	if (enc && !send_context.plaintext) {
		/* random padding */
		for (i = 0; i < padlen; i++) {
			if (i % 4 == 0)
				rnd = arc4random();
			cp[i] = rnd & 0xff;
			rnd >>= 8;
		}
	} else {
		/* clear padding */
		memset(cp, 0, padlen);
	}
	/* packet_length includes payload, padding and padding length field */
	packet_length = buffer_len(&outgoing_packet) - 4;
	cp = buffer_ptr(&outgoing_packet);
	PUT_32BIT(cp, packet_length);
	cp[4] = padlen;
	DBG(debug("send: len %d (includes padlen %d)", packet_length+4, padlen));

	/* compute MAC over seqnr and packet(length fields, payload, padding) */
	if (mac && mac->enabled) {
		macbuf = mac_compute(mac, p_send.seqnr,
		    buffer_ptr(&outgoing_packet),
		    buffer_len(&outgoing_packet));
		DBG(debug("done calc MAC out #%d", p_send.seqnr));
	}
	/* encrypt packet and append to output buffer. */
	cp = buffer_append_space(&output, buffer_len(&outgoing_packet));
	cipher_crypt(&send_context, cp, buffer_ptr(&outgoing_packet),
	    buffer_len(&outgoing_packet));
	/* append unencrypted MAC */
	if (mac && mac->enabled)
		buffer_append(&output, (char *)macbuf, mac->mac_len);
#ifdef PACKET_DEBUG
	fprintf(stderr, "encrypted: ");
	buffer_dump(&output);
#endif
	/* increment sequence number for outgoing packets */
	if (++p_send.seqnr == 0)
		logit("outgoing seqnr wraps around");
	if (++p_send.packets == 0)
		if (!(datafellows & SSH_BUG_NOREKEY))
			fatal("XXX too many packets with same key");
	p_send.blocks += (packet_length + 4) / block_size;
	buffer_clear(&outgoing_packet);

	if (type == SSH2_MSG_NEWKEYS)
		set_newkeys(MODE_OUT);
}

static void
packet_send2(void)
{
	static int rekeying = 0;
	struct packet *p;
	u_char type, *cp;

	cp = buffer_ptr(&outgoing_packet);
	type = cp[5];

	/* during rekeying we can only send key exchange messages */
	if (rekeying) {
		if (!((type >= SSH2_MSG_TRANSPORT_MIN) &&
		    (type <= SSH2_MSG_TRANSPORT_MAX))) {
			debug("enqueue packet: %u", type);
			p = xmalloc(sizeof(*p));
			p->type = type;
			memcpy(&p->payload, &outgoing_packet, sizeof(Buffer));
			buffer_init(&outgoing_packet);
			TAILQ_INSERT_TAIL(&outgoing, p, next);
			return;
		}
	}

	/* rekeying starts with sending KEXINIT */
	if (type == SSH2_MSG_KEXINIT)
		rekeying = 1;

	packet_send2_wrapped();

	/* after a NEWKEYS message we can send the complete queue */
	if (type == SSH2_MSG_NEWKEYS) {
		rekeying = 0;
		while ((p = TAILQ_FIRST(&outgoing))) {
			type = p->type;
			debug("dequeue packet: %u", type);
			buffer_free(&outgoing_packet);
			memcpy(&outgoing_packet, &p->payload,
			    sizeof(Buffer));
			TAILQ_REMOVE(&outgoing, p, next);
			xfree(p);
			packet_send2_wrapped();
		}
	}
}

void
packet_send(void)
{
	if (compat20)
		packet_send2();
	else
		packet_send1();
	DBG(debug("packet_send done"));
}

/*
 * Waits until a packet has been received, and returns its type.  Note that
 * no other data is processed until this returns, so this function should not
 * be used during the interactive session.
 */

int
packet_read_seqnr(u_int32_t *seqnr_p)
{
	int type, len;
	fd_set *setp;
	char buf[8192];
	DBG(debug("packet_read()"));

	setp = (fd_set *)xmalloc(howmany(connection_in+1, NFDBITS) *
	    sizeof(fd_mask));

	/* Since we are blocking, ensure that all written packets have been sent. */
	packet_write_wait();

	/* Stay in the loop until we have received a complete packet. */
	for (;;) {
		/* Try to read a packet from the buffer. */
		type = packet_read_poll_seqnr(seqnr_p);
		if (!compat20 && (
		    type == SSH_SMSG_SUCCESS
		    || type == SSH_SMSG_FAILURE
		    || type == SSH_CMSG_EOF
		    || type == SSH_CMSG_EXIT_CONFIRMATION))
			packet_check_eom();
		/* If we got a packet, return it. */
		if (type != SSH_MSG_NONE) {
			xfree(setp);
			return type;
		}
		/*
		 * Otherwise, wait for some data to arrive, add it to the
		 * buffer, and try again.
		 */
		memset(setp, 0, howmany(connection_in + 1, NFDBITS) *
		    sizeof(fd_mask));
		FD_SET(connection_in, setp);

		/* Wait for some data to arrive. */
		while (select(connection_in + 1, setp, NULL, NULL, NULL) == -1 &&
		    (errno == EAGAIN || errno == EINTR))
			;

		/* Read data from the socket. */
		len = read(connection_in, buf, sizeof(buf));
		if (len == 0) {
			logit("Connection closed by %.200s", get_remote_ipaddr());
			cleanup_exit(255);
		}
		if (len < 0)
			fatal("Read from socket failed: %.100s", strerror(errno));
		/* Append it to the buffer. */
		packet_process_incoming(buf, len);
	}
	/* NOTREACHED */
}

int
packet_read(void)
{
	return packet_read_seqnr(NULL);
}

/*
 * Waits until a packet has been received, verifies that its type matches
 * that given, and gives a fatal error and exits if there is a mismatch.
 */

void
packet_read_expect(int expected_type)
{
	int type;

	type = packet_read();
	if (type != expected_type)
		packet_disconnect("Protocol error: expected packet type %d, got %d",
		    expected_type, type);
}

/* Checks if a full packet is available in the data received so far via
 * packet_process_incoming.  If so, reads the packet; otherwise returns
 * SSH_MSG_NONE.  This does not wait for data from the connection.
 *
 * SSH_MSG_DISCONNECT is handled specially here.  Also,
 * SSH_MSG_IGNORE messages are skipped by this function and are never returned
 * to higher levels.
 */

static int
packet_read_poll1(void)
{
	u_int len, padded_len;
	u_char *cp, type;
	u_int checksum, stored_checksum;

	/* Check if input size is less than minimum packet size. */
	if (buffer_len(&input) < 4 + 8)
		return SSH_MSG_NONE;
	/* Get length of incoming packet. */
	cp = buffer_ptr(&input);
	len = GET_32BIT(cp);
	if (len < 1 + 2 + 2 || len > 256 * 1024)
		packet_disconnect("Bad packet length %u.", len);
	padded_len = (len + 8) & ~7;

	/* Check if the packet has been entirely received. */
	if (buffer_len(&input) < 4 + padded_len)
		return SSH_MSG_NONE;

	/* The entire packet is in buffer. */

	/* Consume packet length. */
	buffer_consume(&input, 4);

	/*
	 * Cryptographic attack detector for ssh
	 * (C)1998 CORE-SDI, Buenos Aires Argentina
	 * Ariel Futoransky([e-mail])
	 */
	if (!receive_context.plaintext &&
	    detect_attack(buffer_ptr(&input), padded_len, NULL) == DEATTACK_DETECTED)
		packet_disconnect("crc32 compensation attack: network attack detected");

	/* Decrypt data to incoming_packet. */
	buffer_clear(&incoming_packet);
	cp = buffer_append_space(&incoming_packet, padded_len);
	cipher_crypt(&receive_context, cp, buffer_ptr(&input), padded_len);

	buffer_consume(&input, padded_len);

#ifdef PACKET_DEBUG
	fprintf(stderr, "read_poll plain: ");
	buffer_dump(&incoming_packet);
#endif

	/* Compute packet checksum. */
	checksum = ssh_crc32(buffer_ptr(&incoming_packet),
	    buffer_len(&incoming_packet) - 4);

	/* Skip padding. */
	buffer_consume(&incoming_packet, 8 - len % 8);

	/* Test check bytes. */
	if (len != buffer_len(&incoming_packet))
		packet_disconnect("packet_read_poll1: len %d != buffer_len %d.",
		    len, buffer_len(&incoming_packet));

	cp = (u_char *)buffer_ptr(&incoming_packet) + len - 4;
	stored_checksum = GET_32BIT(cp);
	if (checksum != stored_checksum)
		packet_disconnect("Corrupted check bytes on input.");
	buffer_consume_end(&incoming_packet, 4);

	if (packet_compression) {
		buffer_clear(&compression_buffer);
		buffer_uncompress(&incoming_packet, &compression_buffer);
		buffer_clear(&incoming_packet);
		buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
		    buffer_len(&compression_buffer));
	}
	type = buffer_get_char(&incoming_packet);
	if (type < SSH_MSG_MIN || type > SSH_MSG_MAX)
		packet_disconnect("Invalid ssh1 packet type: %d", type);
	return type;
}

static int
packet_read_poll2(u_int32_t *seqnr_p)
{
	static u_int packet_length = 0;
	u_int padlen, need;
	u_char *macbuf, *cp, type;
	int maclen, block_size;
	Enc *enc   = NULL;
	Mac *mac   = NULL;
	Comp *comp = NULL;

	if (newkeys[MODE_IN] != NULL) {
		enc  = &newkeys[MODE_IN]->enc;
		mac  = &newkeys[MODE_IN]->mac;
		comp = &newkeys[MODE_IN]->comp;
	}
	maclen = mac && mac->enabled ? mac->mac_len : 0;
	block_size = enc ? enc->block_size : 8;

	if (packet_length == 0) {
		/*
		 * check if input size is less than the cipher block size,
		 * decrypt first block and extract length of incoming packet
		 */
		if (buffer_len(&input) < block_size)
			return SSH_MSG_NONE;
		buffer_clear(&incoming_packet);
		cp = buffer_append_space(&incoming_packet, block_size);
		cipher_crypt(&receive_context, cp, buffer_ptr(&input),
		    block_size);