remove unused variable

[dropbear.git] / packet.c

/*
 * 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 20 /* this is 12 bytes + 0.1% of 8000 bytes */
#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;
        
        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);

        len = writebuf->len - 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");
                }
        } 
        
        ses.last_trx_packet_time = time(NULL);
        ses.last_packet_time = time(NULL);

        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("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");
        }

        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 type;
        unsigned int len, encrypt_buf_size;
        unsigned char mac_bytes[MAX_MAC_LEN];
        
        type = ses.writepayload->data[0];
        TRACE(("enter encrypt_packet()"))
        TRACE(("encrypt_packet type is %d", type))
        
        if (!ses.dataallowed && !packet_is_okay_kex(type)) {
                /* During key exchange only particular packets are allowed.
                        Since this 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, then worst case is if we are 3 away
         * from a blocksize multiple. In which case we need to pad to the
         * multiple, then add another blocksize (or MIN_PACKET_LEN) */
        encrypt_buf_size = (ses.writepayload->len+4+1) + MIN_PACKET_LEN + 3;
        /* add space for the MAC at the end */
        encrypt_buf_size += mac_size;

#ifndef DISABLE_ZLIB
        encrypt_buf_size += ZLIB_COMPRESS_INCR; /* bit of a kludge, but we can't know len*/
#endif
        writebuf = buf_new(encrypt_buf_size);
        buf_setlen(writebuf, PACKET_PAYLOAD_OFF);
        buf_setpos(writebuf, PACKET_PAYLOAD_OFF);

        buf_setpos(ses.writepayload, 0);

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

        /* 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