- Release 4.1p1

[openssh-git.git] / packet.c

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains code implementing the packet protocol and communication
 * with the other side.  This same code is used both on client and server side.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 *
 * SSH2 packet format added by Markus Friedl.
 * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: packet.c,v 1.116 2004/10/20 11:48:53 markus Exp $");

#include "openbsd-compat/sys-queue.h"

#include "xmalloc.h"
#include "buffer.h"
#include "packet.h"
#include "bufaux.h"
#include "crc32.h"
#include "getput.h"

#include "compress.h"
#include "deattack.h"
#include "channels.h"

#include "compat.h"
#include "ssh1.h"
#include "ssh2.h"

#include "cipher.h"
#include "kex.h"
#include "mac.h"
#include "log.h"
#include "canohost.h"
#include "misc.h"
#include "ssh.h"

#ifdef PACKET_DEBUG
#define DBG(x) x
#else
#define DBG(x)
#endif

/*
 * This variable contains the file descriptors used for communicating with
 * the other side.  connection_in is used for reading; connection_out for
 * writing.  These can be the same descriptor, in which case it is assumed to
 * be a socket.
 */
static int connection_in = -1;
static int connection_out = -1;

/* Protocol flags for the remote side. */
static u_int remote_protocol_flags = 0;

/* Encryption context for receiving data.  This is only used for decryption. */
static CipherContext receive_context;

/* Encryption context for sending data.  This is only used for encryption. */
static CipherContext send_context;

/* Buffer for raw input data from the socket. */
Buffer input;

/* Buffer for raw output data going to the socket. */
Buffer output;

/* Buffer for the partial outgoing packet being constructed. */
static Buffer outgoing_packet;

/* Buffer for the incoming packet currently being processed. */
static Buffer incoming_packet;

/* Scratch buffer for packet compression/decompression. */
static Buffer compression_buffer;
static int compression_buffer_ready = 0;

/* Flag indicating whether packet compression/decompression is enabled. */
static int packet_compression = 0;

/* default maximum packet size */
u_int max_packet_size = 32768;

/* Flag indicating whether this module has been initialized. */
static int initialized = 0;

/* Set to true if the connection is interactive. */
static int interactive_mode = 0;

/* Session key information for Encryption and MAC */
Newkeys *newkeys[MODE_MAX];
static struct packet_state {
        u_int32_t seqnr;
        u_int32_t packets;
        u_int64_t blocks;
} p_read, p_send;

static u_int64_t max_blocks_in, max_blocks_out;
static u_int32_t rekey_limit;

/* Session key for protocol v1 */
static u_char ssh1_key[SSH_SESSION_KEY_LENGTH];
static u_int ssh1_keylen;

/* roundup current message to extra_pad bytes */
static u_char extra_pad = 0;

struct packet {
        TAILQ_ENTRY(packet) next;
        u_char type;
        Buffer payload;
};
TAILQ_HEAD(, packet) outgoing;

/*
 * Sets the descriptors used for communication.  Disables encryption until
 * packet_set_encryption_key is called.
 */
void
packet_set_connection(int fd_in, int fd_out)
{
        Cipher *none = cipher_by_name("none");

        if (none == NULL)
                fatal("packet_set_connection: cannot load cipher 'none'");
        connection_in = fd_in;
        connection_out = fd_out;
        cipher_init(&send_context, none, (const u_char *)"",
            0, NULL, 0, CIPHER_ENCRYPT);
        cipher_init(&receive_context, none, (const u_char *)"",
            0, NULL, 0, CIPHER_DECRYPT);
        newkeys[MODE_IN] = newkeys[MODE_OUT] = NULL;
        if (!initialized) {
                initialized = 1;
                buffer_init(&input);
                buffer_init(&output);
                buffer_init(&outgoing_packet);
                buffer_init(&incoming_packet);
                TAILQ_INIT(&outgoing);
        }
}

/* Returns 1 if remote host is connected via socket, 0 if not. */

int
packet_connection_is_on_socket(void)
{
        struct sockaddr_storage from, to;
        socklen_t fromlen, tolen;

        /* filedescriptors in and out are the same, so it's a socket */
        if (connection_in == connection_out)
                return 1;
        fromlen = sizeof(from);
        memset(&from, 0, sizeof(from));
        if (getpeername(connection_in, (struct sockaddr *)&from, &fromlen) < 0)
                return 0;
        tolen = sizeof(to);
        memset(&to, 0, sizeof(to));
        if (getpeername(connection_out, (struct sockaddr *)&to, &tolen) < 0)
                return 0;
        if (fromlen != tolen || memcmp(&from, &to, fromlen) != 0)
                return 0;
        if (from.ss_family != AF_INET && from.ss_family != AF_INET6)
                return 0;
        return 1;
}

/*
 * Exports an IV from the CipherContext required to export the key
 * state back from the unprivileged child to the privileged parent
 * process.
 */

void
packet_get_keyiv(int mode, u_char *iv, u_int len)
{
        CipherContext *cc;

        if (mode == MODE_OUT)
                cc = &send_context;
        else
                cc = &receive_context;

        cipher_get_keyiv(cc, iv, len);
}

int
packet_get_keycontext(int mode, u_char *dat)
{
        CipherContext *cc;

        if (mode == MODE_OUT)
                cc = &send_context;
        else
                cc = &receive_context;

        return (cipher_get_keycontext(cc, dat));
}

void
packet_set_keycontext(int mode, u_char *dat)
{
        CipherContext *cc;

        if (mode == MODE_OUT)
                cc = &send_context;
        else
                cc = &receive_context;

        cipher_set_keycontext(cc, dat);
}

int
packet_get_keyiv_len(int mode)
{
        CipherContext *cc;

        if (mode == MODE_OUT)
                cc = &send_context;
        else
                cc = &receive_context;

        return (cipher_get_keyiv_len(cc));
}
void
packet_set_iv(int mode, u_char *dat)
{
        CipherContext *cc;

        if (mode == MODE_OUT)
                cc = &send_context;
        else
                cc = &receive_context;

        cipher_set_keyiv(cc, dat);
}
int
packet_get_ssh1_cipher(void)
{
        return (cipher_get_number(receive_context.cipher));
}

void
packet_get_state(int mode, u_int32_t *seqnr, u_int64_t *blocks, u_int32_t *packets)
{
        struct packet_state *state;

        state = (mode == MODE_IN) ? &p_read : &p_send;
        *seqnr = state->seqnr;
        *blocks = state->blocks;
        *packets = state->packets;
}

void
packet_set_state(int mode, u_int32_t seqnr, u_int64_t blocks, u_int32_t packets)
{
        struct packet_state *state;

        state = (mode == MODE_IN) ? &p_read : &p_send;
        state->seqnr = seqnr;
        state->blocks = blocks;
        state->packets = packets;
}

/* returns 1 if connection is via ipv4 */

int
packet_connection_is_ipv4(void)
{
        struct sockaddr_storage to;
        socklen_t tolen = sizeof(to);

        memset(&to, 0, sizeof(to));
        if (getsockname(connection_out, (struct sockaddr *)&to, &tolen) < 0)
                return 0;
        if (to.ss_family == AF_INET)
                return 1;
#ifdef IPV4_IN_IPV6
        if (to.ss_family == AF_INET6 &&
            IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)&to)->sin6_addr))
                return 1;
#endif
        return 0;
}

/* Sets the connection into non-blocking mode. */

void
packet_set_nonblocking(void)
{
        /* Set the socket into non-blocking mode. */
        set_nonblock(connection_in);

        if (connection_out != connection_in)
                set_nonblock(connection_out);
}

/* Returns the socket used for reading. */

int
packet_get_connection_in(void)
{
        return connection_in;
}

/* Returns the descriptor used for writing. */

int
packet_get_connection_out(void)
{
        return connection_out;
}

/* Closes the connection and clears and frees internal data structures. */

void
packet_close(void)
{
        if (!initialized)
                return;
        initialized = 0;
        if (connection_in == connection_out) {
                shutdown(connection_out, SHUT_RDWR);
                close(connection_out);
        } else {
                close(connection_in);
                close(connection_out);
        }
        buffer_free(&input);
        buffer_free(&output);
        buffer_free(&outgoing_packet);
        buffer_free(&incoming_packet);
        if (compression_buffer_ready) {
                buffer_free(&compression_buffer);
                buffer_compress_uninit();
        }
        cipher_cleanup(&send_context);
        cipher_cleanup(&receive_context);
}

/* Sets remote side protocol flags. */

void
packet_set_protocol_flags(u_int protocol_flags)
{
        remote_protocol_flags = protocol_flags;
}

/* Returns the remote protocol flags set earlier by the above function. */

u_int
packet_get_protocol_flags(void)
{
        return remote_protocol_flags;
}

/*
 * Starts packet compression from the next packet on in both directions.
 * Level is compression level 1 (fastest) - 9 (slow, best) as in gzip.
 */

static void
packet_init_compression(void)
{
        if (compression_buffer_ready == 1)
                return;
        compression_buffer_ready = 1;
        buffer_init(&compression_buffer);
}

void
packet_start_compression(int level)
{
        if (packet_compression && !compat20)
                fatal("Compression already enabled.");
        packet_compression = 1;
        packet_init_compression();
        buffer_compress_init_send(level);
        buffer_compress_init_recv();
}

/*
 * Causes any further packets to be encrypted using the given key.  The same
 * key is used for both sending and reception.  However, both directions are
 * encrypted independently of each other.
 */

void
packet_set_encryption_key(const u_char *key, u_int keylen,
    int number)
{
        Cipher *cipher = cipher_by_number(number);

        if (cipher == NULL)
                fatal("packet_set_encryption_key: unknown cipher number %d", number);
        if (keylen < 20)
                fatal("packet_set_encryption_key: keylen too small: %d", keylen);
        if (keylen > SSH_SESSION_KEY_LENGTH)
                fatal("packet_set_encryption_key: keylen too big: %d", keylen);
        memcpy(ssh1_key, key, keylen);
        ssh1_keylen = keylen;
        cipher_init(&send_context, cipher, key, keylen, NULL, 0, CIPHER_ENCRYPT);
        cipher_init(&receive_context, cipher, key, keylen, NULL, 0, CIPHER_DECRYPT);
}

u_int
packet_get_encryption_key(u_char *key)
{
        if (key == NULL)
                return (ssh1_keylen);
        memcpy(key, ssh1_key, ssh1_keylen);
        return (ssh1_keylen);
}

/* Start constructing a packet to send. */
void
packet_start(u_char type)
{
        u_char buf[9];
        int len;

        DBG(debug("packet_start[%d]", type));
        len = compat20 ? 6 : 9;
        memset(buf, 0, len - 1);
        buf[len - 1] = type;
        buffer_clear(&outgoing_packet);
        buffer_append(&outgoing_packet, buf, len);
}

/* Append payload. */
void
packet_put_char(int value)
{
        char ch = value;

        buffer_append(&outgoing_packet, &ch, 1);
}
void
packet_put_int(u_int value)
{
        buffer_put_int(&outgoing_packet, value);
}
void
packet_put_string(const void *buf, u_int len)
{
        buffer_put_string(&outgoing_packet, buf, len);
}
void
packet_put_cstring(const char *str)
{
        buffer_put_cstring(&outgoing_packet, str);
}
void
packet_put_raw(const void *buf, u_int len)
{
        buffer_append(&outgoing_packet, buf, len);
}
void
packet_put_bignum(BIGNUM * value)
{
        buffer_put_bignum(&outgoing_packet, value);
}
void
packet_put_bignum2(BIGNUM * value)
{
        buffer_put_bignum2(&outgoing_packet, value);
}

/*
 * Finalizes and sends the packet.  If the encryption key has been set,
 * encrypts the packet before sending.
 */

static void
packet_send1(void)
{
        u_char buf[8], *cp;
        int i, padding, len;
        u_int checksum;
        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(futo@core-sdi.com)
         */
        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);
                cp = buffer_ptr(&incoming_packet);
                packet_length = GET_32BIT(cp);
                if (packet_length < 1 + 4 || packet_length > 256 * 1024) {
#ifdef PACKET_DEBUG
                        buffer_dump(&incoming_packet);
#endif
                        packet_disconnect("Bad packet length %u.", packet_length);
                }
                DBG(debug("input: packet len %u", packet_length+4));
                buffer_consume(&input, block_size);
        }
        /* we have a partial packet of block_size bytes */
        need = 4 + packet_length - block_size;
        DBG(debug("partial packet %d, need %d, maclen %d", block_size,
            need, maclen));
        if (need % block_size != 0)
                fatal("padding error: need %d block %d mod %d",
                    need, block_size, need % block_size);
        /*
         * check if the entire packet has been received and
         * decrypt into incoming_packet
         */
        if (buffer_len(&input) < need + maclen)
                return SSH_MSG_NONE;
#ifdef PACKET_DEBUG
        fprintf(stderr, "read_poll enc/full: ");
        buffer_dump(&input);
#endif
        cp = buffer_append_space(&incoming_packet, need);
        cipher_crypt(&receive_context, cp, buffer_ptr(&input), need);
        buffer_consume(&input, need);
        /*
         * compute MAC over seqnr and packet,
         * increment sequence number for incoming packet
         */
        if (mac && mac->enabled) {
                macbuf = mac_compute(mac, p_read.seqnr,
                    buffer_ptr(&incoming_packet),
                    buffer_len(&incoming_packet));
                if (memcmp(macbuf, buffer_ptr(&input), mac->mac_len) != 0)
                        packet_disconnect("Corrupted MAC on input.");
                DBG(debug("MAC #%d ok", p_read.seqnr));
                buffer_consume(&input, mac->mac_len);
        }
        if (seqnr_p != NULL)
                *seqnr_p = p_read.seqnr;
        if (++p_read.seqnr == 0)
                logit("incoming seqnr wraps around");
        if (++p_read.packets == 0)
                if (!(datafellows & SSH_BUG_NOREKEY))
                        fatal("XXX too many packets with same key");
        p_read.blocks += (packet_length + 4) / block_size;

        /* get padlen */
        cp = buffer_ptr(&incoming_packet);
        padlen = cp[4];
        DBG(debug("input: padlen %d", padlen));
        if (padlen < 4)
                packet_disconnect("Corrupted padlen %d on input.", padlen);

        /* skip packet size + padlen, discard padding */
        buffer_consume(&incoming_packet, 4 + 1);
        buffer_consume_end(&incoming_packet, padlen);

        DBG(debug("input: len before de-compress %d", buffer_len(&incoming_packet)));
        if (comp && comp->enabled) {
                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));
                DBG(debug("input: len after de-compress %d",
                    buffer_len(&incoming_packet)));
        }
        /*
         * get packet type, implies consume.
         * return length of payload (without type field)
         */
        type = buffer_get_char(&incoming_packet);
        if (type < SSH2_MSG_MIN || type >= SSH2_MSG_LOCAL_MIN)
                packet_disconnect("Invalid ssh2 packet type: %d", type);
        if (type == SSH2_MSG_NEWKEYS)
                set_newkeys(MODE_IN);
#ifdef PACKET_DEBUG
        fprintf(stderr, "read/plain[%d]:\r\n", type);
        buffer_dump(&incoming_packet);
#endif
        /* reset for next packet */
        packet_length = 0;
        return type;
}

int
packet_read_poll_seqnr(u_int32_t *seqnr_p)
{
        u_int reason, seqnr;
        u_char type;
        char *msg;

        for (;;) {
                if (compat20) {
                        type = packet_read_poll2(seqnr_p);
                        if (type)
                                DBG(debug("received packet type %d", type));
                        switch (type) {
                        case SSH2_MSG_IGNORE:
                                break;
                        case SSH2_MSG_DEBUG:
                                packet_get_char();
                                msg = packet_get_string(NULL);
                                debug("Remote: %.900s", msg);
                                xfree(msg);
                                msg = packet_get_string(NULL);
                                xfree(msg);
                                break;
                        case SSH2_MSG_DISCONNECT:
                                reason = packet_get_int();
                                msg = packet_get_string(NULL);
                                logit("Received disconnect from %s: %u: %.400s",
                                    get_remote_ipaddr(), reason, msg);
                                xfree(msg);
                                cleanup_exit(255);
                                break;
                        case SSH2_MSG_UNIMPLEMENTED:
                                seqnr = packet_get_int();
                                debug("Received SSH2_MSG_UNIMPLEMENTED for %u",
                                    seqnr);
                                break;
                        default:
                                return type;
                                break;
                        }
                } else {
                        type = packet_read_poll1();
                        switch (type) {
                        case SSH_MSG_IGNORE:
                                break;
                        case SSH_MSG_DEBUG:
                                msg = packet_get_string(NULL);
                                debug("Remote: %.900s", msg);
                                xfree(msg);
                                break;
                        case SSH_MSG_DISCONNECT:
                                msg = packet_get_string(NULL);
                                logit("Received disconnect from %s: %.400s",
                                    get_remote_ipaddr(), msg);
                                cleanup_exit(255);
                                xfree(msg);
                                break;
                        default:
                                if (type)
                                        DBG(debug("received packet type %d", type));
                                return type;
                                break;
                        }
                }
        }
}

int
packet_read_poll(void)
{
        return packet_read_poll_seqnr(NULL);
}

/*
 * Buffers the given amount of input characters.  This is intended to be used
 * together with packet_read_poll.
 */

void
packet_process_incoming(const char *buf, u_int len)
{
        buffer_append(&input, buf, len);
}

/* Returns a character from the packet. */

u_int
packet_get_char(void)
{
        char ch;

        buffer_get(&incoming_packet, &ch, 1);
        return (u_char) ch;
}

/* Returns an integer from the packet data. */

u_int
packet_get_int(void)
{
        return buffer_get_int(&incoming_packet);
}

/*
 * Returns an arbitrary precision integer from the packet data.  The integer
 * must have been initialized before this call.
 */

void
packet_get_bignum(BIGNUM * value)
{
        buffer_get_bignum(&incoming_packet, value);
}

void
packet_get_bignum2(BIGNUM * value)
{
        buffer_get_bignum2(&incoming_packet, value);
}

void *
packet_get_raw(int *length_ptr)
{
        int bytes = buffer_len(&incoming_packet);

        if (length_ptr != NULL)
                *length_ptr = bytes;
        return buffer_ptr(&incoming_packet);
}

int
packet_remaining(void)
{
        return buffer_len(&incoming_packet);
}

/*
 * Returns a string from the packet data.  The string is allocated using
 * xmalloc; it is the responsibility of the calling program to free it when
 * no longer needed.  The length_ptr argument may be NULL, or point to an
 * integer into which the length of the string is stored.
 */

void *
packet_get_string(u_int *length_ptr)
{
        return buffer_get_string(&incoming_packet, length_ptr);
}

/*
 * Sends a diagnostic message from the server to the client.  This message
 * can be sent at any time (but not while constructing another message). The
 * message is printed immediately, but only if the client is being executed
 * in verbose mode.  These messages are primarily intended to ease debugging
 * authentication problems.   The length of the formatted message must not
 * exceed 1024 bytes.  This will automatically call packet_write_wait.
 */

void
packet_send_debug(const char *fmt,...)
{
        char buf[1024];
        va_list args;

        if (compat20 && (datafellows & SSH_BUG_DEBUG))
                return;

        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);

        if (compat20) {
                packet_start(SSH2_MSG_DEBUG);
                packet_put_char(0);     /* bool: always display */
                packet_put_cstring(buf);
                packet_put_cstring("");
        } else {
                packet_start(SSH_MSG_DEBUG);
                packet_put_cstring(buf);
        }
        packet_send();
        packet_write_wait();
}

/*
 * Logs the error plus constructs and sends a disconnect packet, closes the
 * connection, and exits.  This function never returns. The error message
 * should not contain a newline.  The length of the formatted message must
 * not exceed 1024 bytes.
 */

void
packet_disconnect(const char *fmt,...)
{
        char buf[1024];
        va_list args;
        static int disconnecting = 0;

        if (disconnecting)      /* Guard against recursive invocations. */
                fatal("packet_disconnect called recursively.");
        disconnecting = 1;

        /*
         * Format the message.  Note that the caller must make sure the
         * message is of limited size.
         */
        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);

        /* Display the error locally */
        logit("Disconnecting: %.100s", buf);

        /* Send the disconnect message to the other side, and wait for it to get sent. */
        if (compat20) {
                packet_start(SSH2_MSG_DISCONNECT);
                packet_put_int(SSH2_DISCONNECT_PROTOCOL_ERROR);
                packet_put_cstring(buf);
                packet_put_cstring("");
        } else {
                packet_start(SSH_MSG_DISCONNECT);
                packet_put_cstring(buf);
        }
        packet_send();
        packet_write_wait();

        /* Stop listening for connections. */
        channel_close_all();

        /* Close the connection. */
        packet_close();
        cleanup_exit(255);
}

/* Checks if there is any buffered output, and tries to write some of the output. */

void
packet_write_poll(void)
{
        int len = buffer_len(&output);

        if (len > 0) {
                len = write(connection_out, buffer_ptr(&output), len);
                if (len <= 0) {
                        if (errno == EAGAIN)
                                return;
                        else
                                fatal("Write failed: %.100s", strerror(errno));
                }
                buffer_consume(&output, len);
        }
}

/*
 * Calls packet_write_poll repeatedly until all pending output data has been
 * written.
 */

void
packet_write_wait(void)
{
        fd_set *setp;

        setp = (fd_set *)xmalloc(howmany(connection_out + 1, NFDBITS) *
            sizeof(fd_mask));
        packet_write_poll();
        while (packet_have_data_to_write()) {
                memset(setp, 0, howmany(connection_out + 1, NFDBITS) *
                    sizeof(fd_mask));
                FD_SET(connection_out, setp);
                while (select(connection_out + 1, NULL, setp, NULL, NULL) == -1 &&
                    (errno == EAGAIN || errno == EINTR))
                        ;
                packet_write_poll();
        }
        xfree(setp);
}

/* Returns true if there is buffered data to write to the connection. */

int
packet_have_data_to_write(void)
{
        return buffer_len(&output) != 0;
}

/* Returns true if there is not too much data to write to the connection. */

int
packet_not_very_much_data_to_write(void)
{
        if (interactive_mode)
                return buffer_len(&output) < 16384;
        else
                return buffer_len(&output) < 128 * 1024;
}


static void
packet_set_tos(int interactive)
{
#if defined(IP_TOS) && !defined(IP_TOS_IS_BROKEN)
        int tos = interactive ? IPTOS_LOWDELAY : IPTOS_THROUGHPUT;

        if (!packet_connection_is_on_socket() ||
            !packet_connection_is_ipv4())
                return;
        if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, &tos,
            sizeof(tos)) < 0)
                error("setsockopt IP_TOS %d: %.100s:",
                    tos, strerror(errno));
#endif
}

/* Informs that the current session is interactive.  Sets IP flags for that. */

void
packet_set_interactive(int interactive)
{
        static int called = 0;

        if (called)
                return;
        called = 1;

        /* Record that we are in interactive mode. */
        interactive_mode = interactive;

        /* Only set socket options if using a socket.  */
        if (!packet_connection_is_on_socket())
                return;
        if (interactive)
                set_nodelay(connection_in);
        packet_set_tos(interactive);
}

/* Returns true if the current connection is interactive. */

int
packet_is_interactive(void)
{
        return interactive_mode;
}

int
packet_set_maxsize(u_int s)
{
        static int called = 0;

        if (called) {
                logit("packet_set_maxsize: called twice: old %d new %d",
                    max_packet_size, s);
                return -1;
        }
        if (s < 4 * 1024 || s > 1024 * 1024) {
                logit("packet_set_maxsize: bad size %d", s);
                return -1;
        }
        called = 1;
        debug("packet_set_maxsize: setting to %d", s);
        max_packet_size = s;
        return s;
}

/* roundup current message to pad bytes */
void
packet_add_padding(u_char pad)
{
        extra_pad = pad;
}

/*
 * 9.2.  Ignored Data Message
 *
 *   byte      SSH_MSG_IGNORE
 *   string    data
 *
 * All implementations MUST understand (and ignore) this message at any
 * time (after receiving the protocol version). No implementation is
 * required to send them. This message can be used as an additional
 * protection measure against advanced traffic analysis techniques.
 */
void
packet_send_ignore(int nbytes)
{
        u_int32_t rnd = 0;
        int i;

        packet_start(compat20 ? SSH2_MSG_IGNORE : SSH_MSG_IGNORE);
        packet_put_int(nbytes);
        for (i = 0; i < nbytes; i++) {
                if (i % 4 == 0)
                        rnd = arc4random();
                packet_put_char(rnd & 0xff);
                rnd >>= 8;
        }
}

#define MAX_PACKETS     (1U<<31)
int
packet_need_rekeying(void)
{
        if (datafellows & SSH_BUG_NOREKEY)
                return 0;
        return
            (p_send.packets > MAX_PACKETS) ||
            (p_read.packets > MAX_PACKETS) ||
            (max_blocks_out && (p_send.blocks > max_blocks_out)) ||
            (max_blocks_in  && (p_read.blocks > max_blocks_in));
}

void
packet_set_rekey_limit(u_int32_t bytes)
{
        rekey_limit = bytes;
}